The SLL Lighting Handbook

The Society of Light and Lightingis part of the Chartered Institutionof Building Services Engineers

The Society ofLight and Lighting

The SLLLighting

Handbook


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The SLL Lighting Handbook

222 Balham High Road, London SW12 9BS+44 (0)20 8675 5211

www.cibse.org

Final Lighting book artwork 08 25/3/09 10:04 Page 1

This document is based on the best knowledge available at the time of publication. However,no responsibility of any kind for any injury, death, loss, damage or delay however causedresulting from the use of these recommendations can be accepted by the Chartered Institutionof Building Services Engineers, The Society of Light and Lighting, the authors or othersinvolved in its publication. In adopting these recommendations for use each adopter by doingso agrees to accept full responsibility for any personal injury, death, loss, damage or delay arisingout of or in connection with their use by or on behalf of such adopter irrespective of the causeor reason therefore and agrees to defend, indemnify and hold harmless the CharteredInstitution of Building Services Engineers, The Society of Light and Lighting, the authors andothers involved in their publication from any and all liability arising out of or in connectionwith such use as aforesaid and irrespective of any negligence on the part of those indemnified.

The rights of publication or translation are reserved.

No part of this publication may be reproduced, stored in a retrieval system or transmitted inany form or by any means without the prior permission of the publisher.

Note from the publisherThis publication is primarily intended to give guidance. It is not intended to be exhaustive ordefinitive, and it will be necessary for users of the guidance given to exercise their ownprofessional judgement when deciding whether to abide by or depart from it.

© February 2009 The Society of Light and Lighting

The Society is part of CIBSE, which is a registered charity, number 278104.

ISBN 978-1-906846-02-2

Project and Print management byentiveon Ltd. www.entiveon.com

Design, linework and typsetting bySquarefox Design Ltd. www.squarefox.co.uk

Printed in England on FSC certified Mixed Sources paper byStones the Printers Ltd. www.stonestheprinters.co.uk

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The Society of Light and Lightingis part of the Chartered Institutionof Building Services Engineers



FOREWORD

2009 is the centenary of the formation of the Illuminating Engineering Society, the progenitor ofthe Society of Light and Lighting. This handbook has been written to celebrate this anniversaryand to fill a gap in the Society’s publications. The Society of Light and Lighting’s majorpublications are:

The SLL Code for lighting, which offers recommendations on lighting for a wide range of applications

The SLL Lighting Guides, which provide detailed guidance on specific lighting applications

The SLL Lighting Handbook has been written to forge a link between them. It is designed to becomplementary to the SLL Code for lighting but to go beyond it in terms of applications andbackground information without getting into the fine detail of the Lighting Guides.

The SLL Lighting Handbook is intended to be the first-stop for anyone seeking information onlighting. It is aimed not just at lighting practitioners but also at lighting specifiers and students oflighting. For all three groups, we have tried to make it comprehensive, up-to-date and easilyunderstandable. The contents summarise the fundamentals of light and vision, the technology oflighting and guidance on a wide range of applications, both interior and exterior.

AuthorsPeter Boyce PhD, FSLL, FIESNA

Peter Raynham BSc MSc CEng FSLL MCIBSE MILE

AcknowledgementsJohn Fitzpatrick Lou Bedocs (Thorn Lighting)Ted Glenny (Philips Lighting)Jennifer Brons for Figure 20.2Kit Cuttle for Figures 13.1 and 13.2Lighting Research Center for Figures 9.1, 10.3, 18.8, 18.9 and 20.3McGraw Hill Inc, for Figures 2.4 and 2.9Mick Stevens for Figures 20.3 and 22.1The Illuminating Engineering Society of North America for Figures 1.5, 1.6, 1.7, 1.8, 2.8 and 2.13Philips Lighting, iGuzzini Illuminazione, Havells Sylvania & LuxoCharlotte Wood Photography for Figures 14.1, 14.2 and 14.3

EditorsStuart Boreham (entiveon Ltd.)Peter Hadley (Squarefox Design Ltd.)

SLL SecretaryLiz Peck

CIBSE Editorial ManagerKen Butcher

CIBSE Director of InformationJacqueline Balian iii


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CONTENTS

PART 1: FUNDAMENTALS

Chapter 1: Light1.1 The nature of light1.2 The CIE standard observers1.3 The measurement of light — photometry

1.3.1 Luminous flux1.3.2 Luminous intensity1.3.3 Illuminance1.3.4 Luminance1.3.5 Reflectance1.3.6 Obsolete units1.3.7 Typical values

1.4 The measurement of light — colourimetry1.4.1 The CIE chromaticity diagrams1.4.2 The CIE colour spaces1.4.3 Correlated colour temperature1.4.4 CIE colour rendering index1.4.5 Colour gamut1.4.6 Scotopic/photopic ratio 1.4.7 Colour order systems

Chapter 2: Vision2.1 The structure of the visual system

2.1.1 The visual field2.1.2 Eye movements2.1.3 Optics of the eye2.1.4 The structure of the retina 2.1.5 The functioning of the retina 2.1.6 The central visual pathways2.1.7 Colour vision

2.2 Continuous adjustments of the visual system2.2.1 Adaptation2.2.2 Photopic, scotopic and mesopic vision2.2.3 Accommodation

2.3 Capabilities of the visual system2.3.1 Threshold measures2.3.2 Factors determining visual threshold2.3.3 Spatial thresholds2.3.4 Temporal thresholds 2.3.5 Colour thresholds2.3.6 Light spectrum and movement

2.4 Suprathreshold performance2.5 Visual search2.6 Visual discomfort

2.6.1 Insufficient light2.6.2 Illuminance uniformity2.6.3 Glare2.6.4 Veiling reflections2.6.5 Shadows2.6.6 Flicker

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2.7 Perception through the visual system2.7.1 The constancies2.7.2 Attributes and modes of appearance

2.8 Anomolies of vision2.8.1 Defective colour vision2.8.2 Low vision

PART 2: TECHNOLOGY

Chapter 3: Light sources3.1 Production of radiation

3.1.1 Incandescence3.1.2 Electric discharges 3.1.3 Electroluminescence3.1.4 Luminescence3.1.5 Radioluminescence3.1.6 Cathodoluminescence3.1.7 Chemiluminescence3.1.8 Thermoluminescence

3.2 Daylight3.2.1 Sunlight3.2.2 Skylight

3.3 Electric light3.3.1 Incandescent 3.3.2 Tungsten halogen 3.3.3 Fluorescent3.3.4 High pressure mercury3.3.5 Metal halide3.3.6 Low pressure sodium3.3.7 High pressure sodium3.3.8 Induction3.3.9 Light emitting diodes3.3.10 Electroluminescent

3.4 Electric light source characteristics3.4.1 Luminous flux3.4.2 Power demand3.4.3 Luminous efficacy3.4.4 Lumen maintenance3.4.5 Life3.4.6 Colour properties3.4.7 Run-up time3.4.8 Restrike time3.4.9 Other factors3.4.10 Summary of lamp characteristics

3.5 Flames3.5.1 Candle3.5.2 Oil3.5.3 Gas

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Chapter 4: Luminaires4.1 Basic requirements

4.1.1 Electrical4.1.2 Mechanical4.1.3 Optical control4.1.4 Efficiency4.1.5 Thermal 4.1.6 Acoustics4.1.7 Environmental

4.2 Luminaire types4.2.1 Interior lighting4.2.2 Exterior lighting

4.3 Certification and classification4.3.1 Certification4.3.2 Classification

Chapter 5: Electrics5.1 Control gear

5.1.1 Ballasts for discharge light sources5.1.2 Transformers for low voltage light sources5.1.3 Drivers for LEDs

5.2 Lighting controls5.2.1 Options for control5.2.2 Input devices5.2.3 Control processes and systems

PART 3: APPLICATIONS

Chapter 6: Lighting design 6.1 Objectives and constraints6.2 A holistic strategy for lighting

6.2.1 Legal requirements6.2.2 Visual function6.2.3 Visual amenity 6.2.4 Lighting and architectural integration6.2.5 Energy efficiency and sustainability6.2.6 Maintenance6.2.7 Lighting costs6.2.8 Photopic or mesopic vision6.2.9 Light trespass and skyglow

6.3 Basic design decisions6.3.1 Use of daylight6.3.2 Choice of electric lighting system6.3.3 Integration6.3.4 Equal and approved

Chapter 7: Daylighting7.1 Benefits of daylight7.2 Daylight availability7.3 Daylight as a contribution to room brightness7.4 Daylight for task illumination

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7.5 Types of daylighting7.5.1 Windows7.5.2 Clerestories7.5.3 Rooflights7.5.4 Atria7.5.5 Remote distribution7.5.6 Borrowed light

7.6 Problems of daylighting7.6.1 Visual problems7.6.2 Thermal problems7.6.3 Privacy problems

7.7 Maintenance

Chapter 8: Emergency lighting8.1 Legislation and standards8.2 Forms of emergency lighting

8.2.1 Escape route lighting8.2.2 Signage8.2.3 Open area lighting8.2.4 High risk area8.2.5 Standby lighting

8.3 Design approaches8.4 Emergency lighting equipment

8.4.1 Power sources8.4.2 Circuits8.4.3 Luminaires8.4.4 Luminaire classification8.4.5 Light sources8.4.6 Others

8.5 Scheme planning8.5.1 Risk assessment8.5.2 Recommended systems for specific places8.5.3 Planning sequence

8.6 Installation, testing and maintenance8.6.1 Installation8.6.2 Maintenance and inspection8.6.3 Documentation8.6.4 Commissioning and certification8.6.5 Completion certificate

Chapter 9: Office lighting9.1 Functions of lighting in offices9.2 Factors to be considered

9.2.1 Legislation and guidance9.2.2 Type of work done9.2.3 Screen type9.2.4 Daylight availability9.2.5 Ceiling height9.2.6 Obstruction9.2.7 Surface finishes

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9.3 Lighting recommendations9.3.1 Illuminances9.3.2 Light distribution9.3.3 Maximum luminances9.3.4 Discomfort glare control9.3.5 Light source colour properties

9.4 Approaches to office lighting9.4.1 Direct lighting9.4.2 Indirect lighting9.4.3 Direct/indirect lighting9.4.4 Localised lighting9.4.5 Supplementary task lighting9.4.6 Cove lighting9.4.7 Luminous ceilings9.4.8 Daylight

Chapter 10: Industrial lighting10.1 Functions of lighting in industrial premises10.2 Factors to be considered

10.2.1 Legislation and guidance10.2.2 The environment10.2.3 Daylight availability10.2.4 Need for good colour vision10.2.5 Obstruction10.2.6 Directions of view10.2.7 Access10.2.8 Rotating machinery10.2.9 Safety and emergency egress

10.3 Lighting recommendations10.3.1 Control rooms10.3.2 Storage10.3.3 Ancillary areas 10.3.4 Speculative factory units

10.4 Approaches to industrial lighting10.4.1 General lighting10.4.2 Localised lighting10.4.3 Local lighting10.4.4 Visual inspection10.4.5 Visual aids

Chapter 11: Lighting for educational premises11.1 Functions of lighting for educational premises11.2 Factors to be considered

11.2.1 Students’ capabilities11.2.2 Daylight or electric light11.2.3 Common lines of sight11.2.4 Flat or raked floor11.2.5 Presence of visual aids11.2.6 Surface finishes

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11.3 Lighting recommendations11.3.1 Illuminances11.3.2 Illuminance uniformity11.3.3 Glare control11.3.4 Light source colour properties11.3.5 Control systems

11.4 Approaches to lighting educational premises11.4.1 Classrooms and lecture halls11.4.2 IT room11.4.3 Arts studio11.4.4 Science laboratories11.4.5 Seminar room11.4.6 Library11.4.7 Assembly hall11.4.8 Music room11.4.9 Drama studio

Chapter 12: Retail lighting12.1 Functions of retail lighting12.2 Factors to be considered

12.2.1 Shop profile12.2.2 Daylight or electric light12.2.3 Nature of merchandise12.2.4 Obstruction

12.3 Lighting recommendations12.3.1 Illuminances12.3.2 Illuminance uniformity12.3.3 Luminances12.3.4 Light source colour properties

12.4 Approaches to retail lighting 12.4.1 General lighting12.4.2 Accent lighting12.4.3 Display lighting

Chapter 13: Lighting for museums and art galleries13.1 Functions of lighting in museums and art galleries13.2 Factors to be considered

13.2.1 Daylight or electric light13.2.2 Conservation of exhibits13.2.3 Light source colour rendering properties13.2.4 Adaptation13.2.5 Balance13.2.6 Shadows and modelling13.2.7 Glare13.2.8 Veiling reflections and highlights13.2.9 Out-of-hours activities13.2.10 Security and emergency13.2.11 Maintenance13.2.12 Flexibility

13.3 Lighting approaches for museums and art galleries13.3.1 Wall mounted displays13.3.2 Three-dimensional displays13.3.3 Showcase lighting

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Chapter 14: Lighting for hospitals14.1 Functions of lighting in hospitals14.2 Factors to be considered

14.2.1 Daylight14.2.2 Lines of sight14.2.3 Colour rendering requirements14.2.4 Observation without disturbance to sleep14.2.5 Emergency lighting14.2.6 Luminaire safety14.2.7 Cleanliness14.2.8 Electro-magnetic compatibility (EMC)

14.3 Approaches for the lighting of different areas in hospitals14.3.1 Entrance halls, waiting areas and lift halls14.3.2 Reception and enquiry desks14.3.3 Hospital streets and general corridors14.3.4 Changing rooms, cubicles, toilets, bath,

wash and shower rooms14.3.5 Wards14.3.6 Reading lighting 14.3.7 Night lighting14.3.8 Night observation lighting (watch lighting)14.3.9 Clinical areas and operating departments14.3.10 Operating theatres

Chapter 15: Quasi-domestic lighting 15.1 Functions of quasi-domestic lighting15.2 Factors to be considered

15.2.1 Occupants’ capabilities15.2.2 Daylight15.2.3 Light source colour properties15.2.4 Energy efficiency15.2.5 Safety15.2.6 Security

15.3 Lighting recommendations15.4 Approaches to lighting quasi-domestic buildings

15.4.1 Entrances15.4.2 Corridors and stairs 15.4.3 Study bedrooms 15.4.4 Kitchens and utility rooms15.4.5 Lounges15.4.6 Dining halls15.4.7 Games room

Chapter 16: Road lighting16.1 Road classification16.2 Lighting for traffic routes

16.2.1 Lighting recommendations for traffic routes16.2.2 Lighting recommendations for areas

adjacent to the carriageway16.2.3 Lighting recommendations for conflict areas16.2.4 Coordination16.2.5 Traffic route lighting design

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16.3 Lighting for subsidiary roads16.3.1 Lighting recommendations for subsidiary roads16.3.2 Lighting design for subsidiary roads

16.4 Lighting for urban centres and public amenity areas16.5 Tunnel lighting

Chapter 17: Exterior workplace lighting17.1 Functions of lighting in exterior workplaces17.2 Factors to be considered

17.2.1 Scale17.2.2 Nature of work17.2.3 Need for good colour vision17.2.4 Obstruction17.2.5 Interference with complementary activities17.2.6 Hours of operation17.2.7 Impact on the surrounding area17.2.8 Atmospheric conditions

17.3 Lighting recommendations17.3.1 Illuminance and illuminance uniformity17.3.2 Glare control17.3.3 Light source colour properties17.3.4 Loading areas17.3.5 Chemical and fuel industries17.3.6 Sidings, marshalling yards and goods yards

17.4 Approaches to exterior workplace lighting17.4.1 High mast floodlighting 17.4.2 Integrated lighting17.4.3 Localised lighting

Chapter 18: Security lighting18.1 Functions of security lighting18.2 Factors to be considered

18.2.1 Type of site18.2.2 Site features18.2.3 Ambient light levels18.2.4 Crime risk18.2.5 CCTV surveillance18.2.6 Impact on the surrounding area

18.3 Lighting recommendations18.3.1 Illuminance and illuminance uniformity18.3.2 Glare control18.3.3 Light source colour properties

18.4 Approaches to security lighting18.4.1 Secure areas 18.4.2 Public spaces18.4.3 Private areas18.4.4 Multi-occupancy dwellings

18.5 Lighting Equipment18.5.1 Light sources 18.5.2 Luminaires18.5.3 Lighting columns 18.5.4 Lighting controls18.5.5 Maintenance

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Chapter 19: Sports lighting19.1 Functions of lighting for sports19.2 Factors to be considered

19.2.1 Standard of play and viewing distance19.2.2 Playing area19.2.3 Luminaires19.2.4 Television19.2.5 Coping with power failures19.2.6 Obtrusive light

19.3 Lighting recommendations19.3.1 Athletics19.3.2 Bowls19.3.3 Cricket19.3.4 Five-a-side football (indoor)19.3.5 Fitness training19.3.6 Football (Association, Gaelic and American)19.3.7 Lawn tennis19.3.8 Rugby (Union and League)19.3.9 Swimming

19.4 Lighting in large facilities19.4.1 Multi-use sports halls19.4.2 Small sports stadia19.4.3 Indoor arenas19.4.4 Swimming pools

Chapter 20: Lighting performance verification20.1 The need for performance verification20.2 Relevant operating conditions20.3. Instrumentation

20.3.1 Illuminance meters20.3.2 Luminance meters

20.4 Methods of measurement20.4.1 Average illuminance20.4.2 Interior lighting20.4.3 Exterior lighting

20.5 Measurement of illuminance variation20.5.1 Illuminance diversity20.5.2 Illuminance uniformity

20.6 Luminance measurements20.7 Measurement of reflectance

Chapter 21: Lighting maintenance21.1 The need for lighting maintenance21.2 Lamp replacement21.3 Cleaning luminaires21.4 Room surface cleaning21.5 Maintained illuminance21.6 Designing for lighting maintenance21.7 Determination of maintenance factor for interior lighting

21.7.1 Lamp lumen maintenance factor (LLMF)21.7.2 Lamp survival factor (LSF)21.7.3 Luminaire maintenance factor (LMF)21.7.4 Room surface maintenance factor (RSMF)

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21.8 Determination of maintenance factor for exterior lighting21.9 Disposal of lighting equipment

Chapter 22: On the horizon22.1. Changes and challenges22.2. The changes and challenges facing lighting practice

22.2.1 Costs22.2.2 Technologies22.2.3 New knowledge22.2.4 External influences

22.3 The evolution of lighting practice

Chapter 23: Bibliography23.1 Standards23.2 Guidance23.3 References

Index

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PART 1. FUNDAMENTALS

Chapter 1: Light

1.1 The nature of lightLight is part of the electromagnetic spectrum that stretches from cosmic rays to radio waves(Figure 1.1). What distinguishes the wavelength region between 380–780 nanometers fromthe rest is the response of the human visual system. Photoreceptors in the human eyeabsorb energy in this wavelength range and thereby initiate the process of seeing.

Figure 1.1 A schematic diagram of the electromagnetic spectrum showing the location of thevisible spectrum. The divisions between the different types of electromagnetic radiation areindicative only.

1.2 The CIE standard observersThe sensitivity of the human visual system is not the same at all wavelengths in the range380 nm to 780 nm. This makes it impossible to adopt the radiometric quantitiesconventionally used to measure the characteristics of the electromagnetic spectrum forquantifying light. Rather, a special set of quantities has to be derived from the radiometricquantities by weighting them by the spectral sensitivity of the human visual system. Theresult is the photometry system (see Section 1.3).

The Commission Internationale de l’Eclairage (CIE) has established three standardobservers to represent the sensitivity of the human visual system to light at differentwavelengths, in different conditions. In 1924, the CIE adopted the Standard PhotopicObserver to characterise the spectral sensitivity of the human visual system by day.

Wavelength (m)

RADIOWAVES

MICRO WAVES

INFRA RED

ULTRA VIOLET

X RAYS

GAMMA RAYS

COSMIC RAYS

780 nm

380 nm

VISIBLE

104

102

100

10–2

10–4

10–6

10–8

10–10

10–12

10–14

10–16

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In 1990, in the interests of greater photometric accuracy, the CIE produced a ModifiedPhotopic Observer, having greater sensitivity than the CIE Standard Photopic Observer atwavelengths below 460 nm. This CIE Modified Photopic Observer is considered to be asupplement to the CIE Standard Photopic Observer not a replacement for it. As a result, theCIE Standard Photopic Observer has continued to be widely used by the lighting industry. Thisis acceptable because the modified sensitivity at wavelengths below 460 nm has been shown tomake little difference to the photometric properties of light sources that emit radiation over awide range of wavelengths. It is only for light sources that emit significant amounts of radiationbelow 460 nm that changing from the CIE Standard Photopic Observer to the CIE ModifiedPhotopic Observer makes a significant difference to photometric properties. Some narrow bandlight sources, such as blue light emitting diodes, fall into this category.

In 1951, the CIE adopted the CIE Standard Scotopic Observer to characterise the spectralsensitivity of the human visual system by night. The Standard Scotopic Observer is used by the lighting industry to quantify the efficiency of a light source at stimulating the rodphotoreceptors of the eye (see Section 2.1.4).

The CIE Standard and Modified Photopic Observers and the CIE Standard ScotopicObserver are shown in Figure 1.2, the Standard and Modified Photopic Observers havingmaximum sensitivities at 555 nm and the Standard Scotopic Observer having a maximumsensitivity at 507 nm. These relative spectral sensitivity curves are formally known as the1924 CIE Spectral Luminous Efficiency Function for Photopic Vision, the CIE 1988 ModifiedTwo Degree Spectral Luminous Efficiency Function for Photopic Vision, and the 1951 CIESpectral Luminous Efficiency Function for Scotopic Vision, respectively. More commonly,they are known as the CIE V (λ), CIE VM (λ), and the CIE V’ (λ) curves. These curves arethe basis of the conversion from radiometric quantities to the photometric quantities used tocharacterise light.

Figure 1.2 The relative luminous efficiency functions for the CIE Standard Photopic Observer,the CIE Modified Photopic Observer, the CIE Standard Scotopic Observer, and the relativeluminous efficiency function for a 10 degree field of view in photopic conditions

Relative luminousefficiency

= Standard photopic observer

= Modified photopic observer

= Standard scotopic observer

= 10 degree field

Wavelength (nm)

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1.3 The measurement of light — photometry1.3.1 Luminous fluxThe most fundamental measure of the electromagnetic radiation emitted by a source is itsradiant flux. This is the rate of flow of energy emitted and is measured in watts. The mostfundamental quantity used to measure light is luminous flux. Luminous flux is radiant fluxmultiplied, wavelength by wavelength, by the relative spectral sensitivity of the human visualsystem, over the wavelength range 380 nm to 780 nm (Figure 1.3). This process can berepresented by the equation:

where: Φ = luminous flux (lumens)= radiant flux in a small wavelength interval ∆λ (watts)= the relative luminous efficiency function for the conditions

Km= constant (lumens/watt)= wavelength interval

In System Internationale (SI) units, the radiant flux is measured in watts (W) and the luminousflux in lumens (lm). The values of Km are 683 lm/W for the CIE Standard and ModifiedPhotopic Observers and 1699 lm/W for the CIE Standard Scotopic Observer. It is alwaysimportant to identify which of the CIE Standard Observers is being used in any particularmeasurement or calculation. The CIE recommends that whenever the Standard ScotopicObserver is being used, the word scotopic should precede the measured quantity, i.e. scotopicluminous flux. Luminous flux is used to quantify the total light output of a light source in all directions.

Figure 1.3 The process for converting from radiometric to photometric quantities. Thelefthand figure shows the spectral power distribution of a light source in radiometric quantities(watts/wavelength interval). The centre figure shows the CIE Standard Photopic Observer.Multiplying the spectral power at each wavelength by the luminous efficiency at the samewavelength given by the CIE Standard Photopic Observer, the right hand figure is produced.The right hand figure is the spectral luminous flux distribution in photometric quantities(lumens/wavelength interval).

1.3.2 Luminous intensityLuminous intensity is the luminous flux emitted/unit solid angle, in a specified direction. Solidangle is given by area divided by the square of the distance and is measured in steradians. An areaof 1 square metre at a distance of 1 metre from the origin subtends one steradian. The unit ofmeasurement of luminous intensity is the candela, which is equivalent to one lumen/steradian.Luminous intensity is used to quantify the distribution of light from a luminaire.

Φ = Km Σ Ψλ V ∆λλ

Ψλ

Vλ

Energy output V(λ) Light output

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∆λ


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Figure 1.4 Typical illuminances on different surfaces under the noonday sun in temperate climates

1.3.4 LuminanceThe luminance of a surface is the luminous intensity emitted per unit projected area of thesurface in a given direction. The unit of measurement of luminance is the candela/m2.Luminance is widely used to define stimuli presented to the visual system.

1.3.5 ReflectanceAs might be expected, there is a relationship between the amount of light incident on asurface and the amount of light reflected from the same surface. The simplest form of therelationship is quantified by the luminance coefficient. The luminance coefficient is the ratioof the luminance of the surface to the illuminance incident on the surface and has units ofcandela/lumen. The luminance coefficient of a given surface is dependent on the nature ofthe surface and the geometry between the lighting, surface and observer.

There are two other quantities commonly used to express the relationship between theluminance of a surface and the illuminance incident on it. For a perfectly diffusely-reflectingsurface, the relationship is given by the equation:

luminance =

where luminance is expressed in candela/m2 and illuminance is expressed in lumens/m2.

1.3.3 IlluminanceIlluminance is the luminous flux falling on unit area of a surface. The unit of measurement ofilluminance is the lumen/m2 or lux. The illuminance incident on a surface is the mostwidely used electric lighting design criterion. Figure 1.4 shows some typical illuminances ondifferent surfaces under the noonday sun in temperate climates.

100 lux 2500 lux 5000 lux 10,000 lux 100,000 lux

(illuminance × reflectance)π


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tFor a diffusely-reflecting surface, reflectance is defined as the ratio of reflected luminousflux to incident luminous flux. For a non-diffusely-reflecting surface, i.e. a surface with somespecularity, the same equation between luminance and illuminance applies but reflectanceis replaced with luminance factor. Luminance factor is defined as the ratio of the luminanceof the surface viewed from a specific position and lit in a specified way to the luminance of adiffusely-reflecting white surface viewed from the same direction and lit in the same way. Itshould be clear from this definition, that a non-diffusely-reflecting surface can have manydifferent values of the luminance factor. Table 1.1 summarises these definitions.

Table 1.1 The photometric quantities.

Measure

Luminous flux

Luminous intensity

Illuminance

Luminance

Luminance coefficient

Reflectance

For a diffuse surface:

Luminance factor

For a non-diffusesurface, for a specificdirection andlighting geometry:

Units

lumens (lm)

candela (cd)

lumen/m2

candela/m2

candela/lumen

Definition

That quantity of radiant flux which expresses its capacity to produce visual sensation

The luminous flux emitted in a very narrow cone containing the given direction divided by the solid angle of the cone, i.e. luminous flux/unitsolid angle

The luminous flux/unit area at a point on a surface

The luminous flux emitted in a given direction divided by the product of the projectedarea of the source element perpendicular to thedirection and the solid angle containing thatdirection, i.e. luminous intensity/unit area

The ratio of the luminance of a surface to theilluminance incident on it

The ratio of the luminous flux reflected from asurface to the luminous flux incident on it

The ratio of the luminance of a reflecting surfaceviewed from a given direction to that of a perfectwhite uniform diffusing surface identically illuminated

luminance = (illuminance × luminance factor) / π

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1.3.6 Obsolete unitsPhotometry has a long history that has generated a number of different units ofmeasurement for illuminance and luminance. Table 1.2 lists some of these obsolete units,together with the multiplying factors necessary to convert from the alternative unit to the SIunits of lumens/m2 for illuminance and candela/m2 for luminance.

Table 1.2 Some photometric units of measurement for illuminance and luminance and themultiplying factors necessary to change them to System Internationale (SI) units

* Luminous exitance is the product of the illuminance on the surface and the reflectance of the surface. It is only meaningful for completely diffusely reflecting surfaces. Luminous exitance has the dimensions of lumens/unit area. Luminous exitance is deprecated in the SI system.

1.3.7 Typical valuesTable 1.3 shows some illuminances and luminances typical of commonly occurringsituations, all measured using the CIE Standard Photopic Observer.

Quantity

Illuminance

Luminance

Luminous exitance*

Unit

lux metre candle

photfootcandle

nit stilb

apostilb* blondel* lambert*

footlambert*

Dimensions

lumen/m2

lumen/m2

lumen/cm2

lumen/ft2

candela/m2

candela/cm2

candela/in2

candela/ft2

lumen/m2

lumen/m2

lumen/cm2

lumen/ft2

Multiplying factor

1.001.00

10,00010.76

1.0010,0001,55010.76

0.320.323,1833.43

Situation

Clear sky in summerin temperate zones

Overcast sky in summerin temperate zones

Textile inspection

Office work

Heavy engineering

Good road lighting

Moonlight

Illuminance (lm/m2)

100,000

16,000

1,500

500

300

20

0.5

Typical surface

Grass

Grass

Light grey cloth

White paper

Steel

Concrete road surface

Asphalt road surface

Luminance (cd/m2)

1,910

300

140

120

20

2.0

0.01

Table 1.3 Typical illuminance and luminance values.


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1.4 The measurement of light — colourimetry

Photometry does not take into account the wavelength combination of the light. Thus it ispossible for two surfaces to have the same luminance but the reflected light to be made upof totally different combinations of wavelengths. In this situation, and provided there isenough light for colour vision to operate, the two surfaces will look different in colour. TheCIE colourimetry system provides a means to quantify colour.

1.4.1 The CIE chromaticity diagramsThe basis of the CIE colourimetry system is colour matching. The CIE Colour MatchingFunctions are the relative spectral sensitivity curves of the human observer with normalcolour vision and can be considered as another form of standard observer. The CIE colourmatching functions are mathematical constructs that reflect the relative spectral sensitivitiesrequired to ensure that all the wavelength combinations that are seen as the same colourhave the same position in the CIE colourimetry system and that all wavelengthcombinations that are seen as different in colour occupy different positions. Figure 1.5 showstwo sets of colour matching functions. The CIE 1931 Standard Observer is used for coloursoccupying visual fields up to 4° of angular subtense. The CIE 1964 Standard Observer isused for colours covering visual fields greater than 4° in angular subtense. The values ofthe colour matching functions at different wavelengths are known as the spectral tristimulus values.

Figure 1.5 Two sets of colour matching functions: The CIE 1931standard observer (2 degrees)(solid line) and the CIE 1964 standard observer (10 degrees) (dashed line).

2.5

2.0

1.5

1.0

0.5

0

z

y x

400 450 500 550 600 650 700

Wavelength (nm)

The colour of a light source can be represented mathematically by multiplying the spectralpower distribution of the light source, wavelength by wavelength, by each of the three colourmatching functions x(λ), y(λ) and z(λ), the outcome being the amounts of three imaginaryprimary colours X, Y, and Z required to match the light source colour. In the form ofequations, X, Y and Z are given by:


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X = h Σ S(λ) x(λ) λY = h Σ S(λ) y(λ) λZ = h Σ S(λ) z(λ) λ

where: S(λ) = spectral radiant flux of the light source (W/nm)x(λ), y(λ), z(λ) = spectral tristimulus values from the appropriate

colour matching functionλ = wavelength interval (nm)h = arbitrary constant

If only relative values of the X, Y and Z are required, an appropriate value of h is one thatmakes Y = 100. If absolute values of the X, Y, and Z are required it is convenient to take h = 683 since then the value of Y is the luminous flux in lumens.

If the colour being calculated is for light reflected from a surface or transmitted through amaterial, the spectral reflectance or spectral transmittance is included as a multiplier in theabove equations. For a reflecting surface, an appropriate value of h is one that makes Y =100 for a perfect white reflecting surface because then the actual value of Y is thepercentage reflectance of the surface.

Having obtained the X, Y, and Z values, the next step is to express their individual values asproportions of their sum, i.e.

x = X / (X+Y+Z) y = Y / (X+Y+Z) z = Z / (X+Y+Z)

The values x, y and z are known as the CIE chromaticity coordinates. As x + y + z = 1, only twoof the coordinates are required to define the chromaticity of a colour. By convention, the x and ycoordinates are used. Given that a colour can be represented by two coordinates, then all colourscan be represented on a two dimensional surface. Figure 1.6 shows the CIE 1931 chromaticitydiagram. The outer curved boundary of the CIE 1931 chromaticity diagram is called the spectrumlocus. All pure colours, i.e. those that consist of a single wavelength, lie on this curve. The straightline joining the ends of the spectrum locus is the purple boundary and is the locus of the mostsaturated purples obtainable. At the centre of the diagram is a point called the equal energy point,where a colourless surface will be located. Close to the equal energy point is a curve called thePlanckian locus. This curve passes through the chromaticity coordinates of objects that operate as a black body, i.e. the spectral power distribution of the light source is determined solely by its temperature.

The CIE 1931 chromaticity diagram can be considered as a map of the relative location ofcolours. The saturation of a colour increases as the chromaticity coordinates get closer tothe spectrum locus and further from the equal energy point. The hue of the colour isdetermined by the direction in which the chromaticity coordinates move. The CIE 1931chromaticity diagram is useful for indicating approximately how a colour will appear, a valuerecognised by the CIE in that it specifies chromaticity coordinate limits for signal lights andsurfaces so that they will be recognised as red, green, yellow, and blue (CIE Publication107:1994).


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Figure 1.6 The CIE 1931 Chromaticity Diagram showing the spectrum locus, the Planckianlocus and the equal energy point)

The CIE 1931 chromaticity diagram is perceptually non-uniform. Green colours cover alarge area while red colours are compressed in the bottom right corner. This perceptualnon-uniformity makes any attempt to quantify large colour differences using the CIE 1931chromaticity diagram futile. In an attempt to improve this situation, the CIE first introducedthe CIE 1960 Uniform Chromaticity Scale (UCS) diagram and then, in 1976, recommendedthe use of the CIE 1976 UCS diagram. Both diagrams are simply linear transformations of theCIE 1931 chromaticity diagram. The axes for the CIE 1976 UCS diagram are

u' = 4x / (–2x +12y +3) v' = 9y / (–2x + 12y + 3)

where x and y are the CIE 1931 chromaticity coordinates. Figure 1.7 shows the CIE 1976 UCS diagram.

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

520 nanometers

480 nanometers

490

560

470

550

460

540

450

530

570

0.2

580

510

24,000

380

500

Y

X

0.1 0.3 0.4 0.5 0.6 0.7 0.80

Equalenergy

10,000

6500

4800

3500590

600

510

620630

640

780

2360 19001500


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Figure 1.7 The CIE 1976 Uniform Chromaticity Scale diagram (from the IESNA Lighting Handbook)

1.4.2 The CIE colour spacesAll chromaticity diagrams are of limited value for quantifying colour differences becausesuch diagrams are two-dimensional, considering only the hue and saturation of the colour.To completely describe a colour a third dimension is needed, that of brightness for a self-luminous object and lightness for a reflecting object. In 1964, the CIE introduced the U*, V*,W* colour space for use with surface colours, where

U* = 13 W* (u – un)V* = 13 W* (v – vn)W* = 25 Y0.33 – 17 (where Y has a range from 1 to 100)

W* is called a lightness index and approximates the Munsell value of a surface colour (seeSection 1.4.7). The coordinates u, v, refer to the chromaticity coordinates of the surfacecolour in the CIE 1960 UCS diagram while the chromaticity coordinates un, vn refer to aspectrally neutral colour lit by the source, that is placed at the origin of the U*, V* system. This U*, V*, W* system is little used now, about the only purpose for which it is routinelyused is the calculation of the CIE colour rendering indices (see Section 1.4.4). For otherpurposes, the U*, V*, W* colour space has been superseded by two other colourspaces known by the initialisms CIELUV and CIELAB.

0.6

0.5

0.4

0.3

0.2

0.1

520

480

560

470

460

540

450

0.2

580

500

0.1 0.3 0.4 0.5 0.60

600

620640

770 nm

440400 nm420

V '

U '


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tThe three coordinates of the CIELUV colour space are given by the expressions:

L* = (116 (Y/Yn) 0.33 – 16) for Y/Yn > 0.008856

L* = 903.29 (Y/Yn) for Y/Yn ≤ 0.008856

u* = 13 L* (u' – u'n)

v* = 13 L* (v' – v'n)

where u' and v' are the chromaticity coordinates from the CIE 1976 UCS diagram and u'n,v'n, Yn are values for a nominally achromatic colour, usually the surface with 100%reflectance (Y = 100) lit by the light source.

The three coordinates of the CIELAB colour space are given by the expressions:

L* = 116 f (Y/Yn) – 16

a* = 500 (f(X/Xn) – f(Y/Yn))

b* = 200(f(Y/Yn) – f(Z/Zn))

where f(q) = q for q > 0.008856 and f(q) = 7.787 q + 0.1379 for q ≤ 0.008856

q = X/Xn or Y/Yn or Z/Zn

Again, Xn, Yn, Zn are the values of the X, Y and Z for a nominally achromatic surface,usually that of the light source with Yn = 100.

Each of these colour spaces have a colour difference formula associated with them. For theCIELUV colour space, the colour difference is given by

E*uv = ((L*)2 + (u*)2 + (v*)2)0.5

For the CIELAB colour space, the colour difference is given by

E*ab = ((L*)2 + (a*)2 + (b*)2)0.5

These two colour spaces are now widely used to set colour tolerances for manufacture in many industries.

1.4.3 Correlated colour temperatureWhile the CIE colourimetry system is the most exact means of quantifying colour, it iscomplex. Therefore, the lighting industry has used the CIE colourimetry system to derivetwo single-number metrics to characterise the colour properties of light sources. The metricused to characterise the colour appearance of the light emitted by a light source is thecorrelated colour temperature. The basis of this measure is the fact that the spectral powerdistribution of a black body is defined by Planck's Radiation Law and hence is a function ofits temperature only (see Section 3.1.1).

0.33


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Figure 1.8 shows a section of the CIE 1931 chromaticity diagram with the Planckian locusshown. The locus is the curved line joining the chromaticity coordinates of black bodies atdifferent temperatures. The lines running across the Planckian locus are iso-temperature lines.When the CIE 1931 chromaticity coordinates of a light source lie directly on the Planckianlocus, the colour appearance of that light source is expressed by the colour temperature, i.e. thetemperature of the black body that has the same chromaticity coordinates. For light sources thathave chromaticity coordinates close to the Planckian locus but not on it, their colourappearance is quantified as the correlated colour temperature, i.e. the temperature of the iso-temperature line that is closest to the actual chromaticity coordinates of the light source. Thetemperatures are usually given in kelvins (K).

As a rough guide, nominally-white light sources have correlated colour temperaturesranging from 2,700 K to 7,500 K. A 2,700 K light source, such as an incandescent lamp, willhave a yellowish colour appearance and be described as ‘warm’, while a 7,500 K lamp,such as some types of fluorescent lamp, will have a bluish appearance and be described as‘cold’. It is important to appreciate that light sources that have chromaticity coordinates thatlie beyond the range of the iso-temperature lines shown in Figure 1.8 should not be given acorrelated colour temperature. The light from such light sources will appear greenish whenthe chromaticity coordinates lie above the Planckian locus or purplish if they lie below it.

Figure 1.8 The Planckian locus and lines of constant correlated colour temperature plotted onthe CIE 1931 (x,y) chromaticity diagram. Also shown are the chromaticity coordinates of CIEStandard Illuminants, A, C, and D65 (from the IESNA Lighting Handbook).

1.4.4 CIE colour rendering indexThe CIE colour rendering index measures how well a given light source renders a set ofstandard test colours relative to their rendering under a reference light source of the samecorrelated colour temperature as the light source of interest.

0.500

0.400

0.300

0.200

0.200 0.300 0.400 0.500 0.600

X

Y

C

0

10,0

00

5,00

0

3,33

3 2,50

0

2,00

0

1,51

5

D65

A


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tThe reference light source used is an incandescent light source for light sources with a correlatedcolour temperature below 5000 K and some form of daylight for light sources with correlatedcolour temperature above 5000 K. The actual calculation involves obtaining the positions of asurface colour in the CIE 1964, U*, V*, W*, colour space under the reference light source andunder the light source of interest, correcting for any difference in white point under the twolight sources and expressing the difference between the two positions on a scale that gives perfectagreement between the two positions a value of 100. The CIE has fourteen standard test colours.The first eight form a set of pastel colours arranged around the hue circle. Test colours nine tofourteen represent colours of special significance, such as skin tones and vegetation. The result of the calculation for any single colour is called the CIE special colour rendering index, for that colour. The average of the special colour rendering indices for the first eight test colours is called the CIE general colour rendering index (Ra). It is the CIE general colour renderingindex that is usually presented in light source manufacturers’ catalogues. The CIE general colourrendering index varies widely across light sources (see Section 3.4.10).

1.4.5 Colour gamutThe colour gamut of a light source is obtained by calculating the position of the first eight CIEstandard test colours under the light source of interest and plotting them on the CIE 1976 UCSdiagram. When the plotted positions are joined together, the colour gamut is formed. The colourgamut can be reduced to a single number by calculating the gamut area. Figure 1.9 shows thecolour gamuts for a number of different light sources. A great deal can be learnt from the colourgamut. From a consideration of its shape and the spacing between the positions of the individualtest colours, the extent to which the different parts of the hue circle can be discriminated isapparent. From its location on the CIE 1976 UCS diagram, the appearance of colours can beappreciated to some degree. By plotting different light sources on the same diagram it is easy tomake comparisons between light sources. Further, by including the colour gamut of an ideal lightsource, such as daylight, it is possible to evaluate how close to the ideal light source is the lightsource of interest, as far as colour rendering is concerned.

+

*

+

+

+

+

+

+

+

+

*

*

*

*

*

**

*

Figure 1.9 The colour gamuts for high pressure sodium, incandescent, fluorescent and metalhalide light sources, and for the CIE Standard Illuminant D65, simulating daylight, all plotted onthe CIE 1976 uniform chromaticity scale diagram. The dotted curve is the Planckian locus.

0.58

0.56

0.54

0.52

0.50

0.48

0.46

0.44

0.42

0.14

= spectrum locus

= Planckian locus

= metal halide

= high pressure sodium

= fluorescent

= incandescent

= daylight

0.16 0.18 0.20 0.22 0.24 0.26 0.28 0.30 0.32 0.34

V'

U '


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1.4.6 Scotopic/photopic ratioOne other measure of light source colour characteristics that has been gaining interest inrecent years is the scotopic/photopic ratio (Berman, 1992). This is calculated by taking therelative spectral power distribution, in radiometric units, of the light source and weighting itby the CIE Standard Scotopic and Photopic Observers and expressing the resultingscotopic lumens and photopic lumens as a ratio. The value of scotopic/photopic ratios isthat they express the relative effectiveness of different light sources in stimulating the rodand cone photoreceptors in the human visual system. A light source with a higherscotopic/photopic ratio will stimulate the rods more than a light source with a lowerscotopic/photopic ratio when both produce the same photopic luminous flux. Thisinformation is useful when considering light sources for applications where the operation ofboth rod and cone photoreceptors is likely. Table 1.4 gives scotopic/photopic ratios for anumber of commonly used light sources.

Table 1.4 Scotopic/photopic ratios for a number of widely used electric light sources (fromHe et al., 1997)

Light source

Incandescent

Fluorescent

Mercury vapour

Metal halide

High pressure sodium

Low pressure sodium

Photopic efficacy (lm/W)

14.7

84.9

52.3

107.4

126.9

180.0

Scotopic efficacy (lm/W)

20.3

115.9

66.8

181.7

80.5

40.8

Scotopic/photopic ratio

1.38

1.36

1.28

1.69

0.63

0.23

1.4.7 Colour order systemsA colour ordering system is a physical, three-dimensional representation of colour space.There are several different colour ordering systems but one of the most widely used is theMunsell system. Figure 1.10 shows the organisation of the Munsell system. The azimuthalhue dimension consists of 100 steps arranged around a circle, with five principal hues (red,yellow, green, blue and purple) and five intermediate hues (yellow-red, green-yellow, blue-green, purple-blue and red-purple). The vertical value scale contains ten steps from black towhite. The horizontal chroma scale contains up to 20 steps from gray to highly saturated. Theposition of any colour in the Munsell system is identified by an alphanumeric reference madeup of three terms, hue, value and chroma, e.g. a strong red is given the alphanumeric 7.5R/4/12.Achromatic surfaces, i.e. colours that lie along the vertical value axis and hence have no hue orchroma, are coded as Neutral 1, Neutral 2 etc. depending on their reflectance. To a firstapproximation, the percentage reflectance of a surface is given by the product of V and (V–1) ofthe surface, where V is the Munsell value of the surface.


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Figure 1.10 The organisation of the Munsell colour order system. The hue letters are B =blue, PB = purple/blue, P = purple, RP = red/purple, R = red, YR = yellow/red, Y = yellow,GY = green/yellow, G = green, BG = blue/green.

The existence of several other colour ordering systems, such as the Natural Colour System,the DIN system and BS 5252 system, would seem to be a recipe for confusion. This isavoided by the fact that conversions are available between many of the colour orderingsystems. For more detail on the Munsell system, other colour ordering systems and therelationships between them, see the SLL Lighting Guide 11: Surface reflectance and colour.

White

1 2 3 4 5 6

Black

Chroma scale

Hue scale

Value scale

7

8

9

10

5P10P

5RP

10RP

10R

5R

5YR

1

2

4

6

10YR

5Y

10Y10GY

5GY

5G

10G

10BG

5BG

5B 10B5PB

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Chapter 2: Vision

2.1 The structure of the visual system

The visual system consists of the eye and brain working together. Functionally, the visualsystem is an image-processing system that extracts specific aspects of the retinal image forinterpretation by the brain.

2.1.1 The visual fieldHumans have two eyes, mounted frontally. Figure 2.1 shows the approximate extent of thevisual field of the two eyes in humans, measured in degrees from the point of fixation. Theenclosed white area can be seen with both eyes. The shaded area to the left is visible to theleft eye only. The shaded area to the right is visible to the right eye only.

Figure 2.1 The binocular visual field expressed in degrees deviation from the point offixation. The shaded areas are visible to only one eye (after Boff and Lincoln, 1988).

Given this limited field of view for a fixed position, it is necessary for the two eyes to be able to move. There are two ways this can be done; by moving the head and by moving theeyes in the head. Humans have a limited range of head movements but a wide range of eye movements.

2.1.2 Eye movementsThe movement of the eye in its socket is controlled by six extra-ocular muscles arranged inopposing pairs. The pattern of eye movements used when examining a visual sceneconsists of a series of fixations and saccades. Fixations are attempts to keep the retinalimage of the object of interest on the fovea. Figure 2.2 shows a pattern of fixation points fortwo people examining the seams on a pair of briefs.

100

80

60

20

40

20

40

60

80

100


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Figure 2.2 The pattern of fixations made by two inspectors examining men’s briefs held ona frame. S = start of scan path, C = end of scan of front and one side, rotation of frame andcontinuation of scan across back and sides, E = end of scan. Inspector M examines only theseams while Inspector D examines the fabric as well (after Megaw and Richardson, 1979).

Movement between the fixation points is made by saccades. Saccades are very fast,velocities ranging up to 1000 degrees/second depending upon the distance moved.Saccadic eye movements have a latency of about 200 ms, which limits how frequently theline of sight can be moved to about five movements per second. Visual functions aresubstantially limited during saccadic movements. Fixations and saccades both occur in asingle eye, but movements in the two eyes are not independent. Rather, they arecoordinated so that the lines of sight of the two eyes are both pointed at the same target atthe same time. Movements of the two eyes that keep the primary lines of sight convergedon a target, or which may be used to switch fixation from a target at one distance to a newtarget in the same direction but at a different distance, are called vergence movements.These movements are very slow, up to 10 degrees/second, and can occur as a jumpmovement or can smoothly follow a target moving in a fore-and-aft direction. Both types ofmovement involve a change in the angle between the two eyes.

2.1.3 Optics of the eyeFigure 2.3 shows a section through the eye, the upper and lower halves being adjusted forfocus at near and far distances, respectively. The eye is basically spherical with a diameterof about 24 mm. The sphere is formed from three concentric layers. The outermost layer,called the sclera, protects the contents of the eye and maintains its shape under pressure.Over most of the eye’s surface, the sclera looks white but at the front of the eye the sclerabulges up and becomes transparent. It is through this area, called the cornea, that lightenters the eye. The next layer is the vascular tunic, or choroid. This layer contains a densenetwork of small blood vessels that provide oxygen and nutrients to the next layer, theretina. As the choroid approaches the front of the eye it separates from the sclera and formsthe ciliary body. This element produces the watery fluid that lies between the cornea and thelens, called the aqueous humor. The aqueous humor provides oxygen and nutrients to thecornea and the lens, and takes away their waste products. Elsewhere in the eye this is doneby blood but on the optical pathway through the eye, a transparent medium is necessary.

S S

C

C

C

C

E

E

M D


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As the ciliary body extends further away from the sclera, it becomes the iris. The iris forms acircular opening, called the pupil, that admits light into the eye. Pupil size varies with theamount of light reaching the retina but it is also influenced by the distance of the object fromthe eye, the age of the observer and by emotional factors such as fear, excitement and anger.

Figure 2.3 A section through the eye adjusted for near and distant vision

After passing through the pupil, light reaches the lens. The lens is fixed in position, butvaries its focal length by changing its shape. The change in shape is achieved bycontracting or relaxing the ciliary muscles. For objects close to the eye, the lens is fattened.For objects far away, the lens is flattened.

The space between the lens and the retina is filled with another transparent material, thejelly-like vitreous humor. After passing though the vitreous humor, light reaches the retina,the location where light is absorbed and converted to electrical signals. The retina is acomplex structure, as can be seen from Figure 2.4. It can be considered as having threelayers: a layer of photoreceptors, which can be divided into four types; a layer of collectorcells which provide links between multiple photoreceptors, and a layer of ganglion cells. The axons of the ganglion cells form the optic nerve which produces the blind spot where itpasses through the retina out of the eye. Light reaching the retina, passes through theganglion and collector cell layers before reaching the photoreceptors, where it is absorbed.Any light that gets through the photoreceptor layer is absorbed by the pigment epitheliummounted on Bruch’s membrane.

Iris contracted

Distant vision

Pupil

Cornea

Iris opened

Lens flattened

Sclera

Blindspot

Opticnerve

Cilarymuscle

Near vision

FoveaRetina

Lens rounded


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Figure 2.4 A section through the retina (after Sekular and Blake, 1994)

2.1.4 The structure of the retinaThe retina is an extension of the brain. The visual system has four photoreceptor types inthe retina, each containing a different photopigment. These four types are conventionallygrouped into two classes, rods and cones. All the rod photoreceptors are the same,containing the same photopigment and hence having the same spectral sensitivity. Therelative spectral sensitivity of the rod photoreceptors is shown in Figure 2.5. The other threephotoreceptor types are all cones, each with a different photopigment. Figure 2.6 shows therelative spectral sensitivity functions of the three cone photoreceptor types, called short (S),medium (M) and long (L) wavelength cones.

Retinalganglioncell axons

Vitreous

Light

Retinalganglioncells

Collectorcells

Receptors

Pigment epithelium

Bruch’s membrane

Choroid


Figure 2.5 Log relative luminous efficiency of the rod photoreceptor

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Figure 2.6 The relative spectral sensitivities of long wavelength (L), medium wavelength (M)and short wavelength (S) cone photoreceptors (after Kaiser and Boynton, 1996)

Rods and cones are distributed differently across the retina (Figure 2.7). Cones are concentrated inone small area that lies on the visual axis of the eye, called the fovea, although there is a lowdensity of cones across the rest of the retina.

Log relative luminous efficiency

Wavelength (nm)

400 420 440 460 480 500 520 540 560 580 600 620 640 680 700660

0

–0.5

–1.0

–1.5

–2.0

–2.5

–3.0

–3.5

–4.0

–4.5

–5.0

Wavelength (nm)

Relative sensitivity

350 400 450 500 550 600 650 700 750

Long wavelength cones

Medium wavelength cones

Short wavelength cones

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0


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Figure 2.7 The distribution of rod and cone photoreceptors across the retina. The 0 degreeindicates the position of the fovea.

The three cone types are also not distributed equally across the retina. The L- and M-conesare concentrated in the fovea, their density declining gradually with increasing eccentricity.The S-cones are largely absent from the fovea; reach a maximum concentration just outsidethe fovea and then decline gradually in density with increasing eccentricity.

Over the whole retina there are approximately 120 million rods and 8 million cones. The factthat there are many more rod than cone photoreceptors should not be taken to indicate thathuman vision is dominated by the rods. It is the fovea that allows resolution of detail and otherfine discriminations and the fovea is entirely inhabited by cones. There are three otheranatomical features that emphasise the importance of the fovea. The first is the absence of bloodvessels. The second is that the collector and ganglion layers of the retina are pulled away over thefovea. The third is the fact that the outer limb of the cone photoreceptor can act as a waveguide,making cones most sensitive to light rays passing through the centre of the lens. This lastcharacteristic, known as the Stiles-Crawford effect, compensates to some extent for the poorquality of the eye’s optics by making the fovea less sensitive to light passing through the edge ofthe lens or scattered in the optic media. The fovea is populated only with cones. Rodphotoreceptors, which dominate the population of the rest of the retina, do not show a Stiles-Crawford effect.

Eccentricity (degrees)

Density (thousands /mm2)

200

150

100

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2.1.5 The functioning of the retinaThe retina is where the processing of the retinal image begins. Recordings of electricaloutput from single ganglion cells have shown a number of important characteristics. Thefirst is that the electrical discharge is a series of voltage spikes of equal amplitude.Variations in the amount of light falling on the photoreceptors supplying signals to the ganglioncell through the network of collector cells, produce changes in the frequency with which thesevoltage spikes occur but not in their amplitude. The second is that there is a level of electricaldischarge present even when there is no light falling on the photoreceptors, called thespontaneous discharge. The third is that illuminating photoreceptors with a spot of light, canproduce either an increase or a decrease in the frequency of electrical discharges, relative to thelevel of frequency of discharges present when light is absent.

Further studies of the pattern of electrical discharges from a single ganglion cell have revealedtwo other important aspects of the operation of the retina. The first is the existence of receptivefields. A receptive field is the area of the retina that determines the output from a singleganglion cell. A receptive field always represents the activity of a number of photoreceptors, andoften reflects input from different cone types as well as from rods. The sizes of receptive fieldsvary systematically with retinal location. Receptive fields around the fovea are very small. Aseccentricity from the fovea increases, so does receptive field size.

Within each receptive field there is a specific structure. Receptive fields consist of a centralcircular area and a surrounding annular area. These two areas have opposing effects on theganglion cell’s electrical discharge. Either the central area increases and the annular surrounddecreases the rate of electrical discharge, or, in other receptive fields, the reverse occurs. Thesetypes of receptive fields are known as on-centre/off-surround and off-centre/on-surround fields,respectively. If either of these two types of retinal receptive fields is illuminated uniformly, thetwo types of effect on electrical discharge cancel each other, a process called lateral inhibition.However, if the illumination is not uniform across the two parts of the receptive field, a neteffect on the ganglion cell discharge is evident. This pattern of response makes the retinal fieldswell suited to detect boundaries in the retinal image.

While every retinal ganglion cell has a receptive field, not every ganglion cell is the same. Infact, there are two types of ganglion cell, called magnocellular (M) cells and parvocellular (P)cells. There are a number of important differences between the M-cells and P-cells. First, theaxons of the M-cells are thicker than the axons of the P-cells, indicating that signals aretransmitted more rapidly from the M-cells than from the P-cells. Second there are many moreP-cells than M-cells and they are distributed differently across the retina. The P-cells dominatein the fovea and parafovea and the M-cells dominate in the periphery. Third, for a giveneccentricity, the P-cells have smaller receptive fields than the M-cells. Fourth, the M-cells andP-cells are sensitive to different aspects of the retinal image. The M-cells are more sensitive torapidly varying stimuli and to small differences in illumination but are insensitive to differencesin colour. The P-cells are more sensitive to small areas of light and to colour.

This brief description shows that the retina extracts information on boundaries in the retinalimage and then extracts specific aspects of the stimulus within the boundaries, such as colour.These aspects are then transmitted up the optic nerve, formed from the axons of the retinalganglion cells, along different channels.


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Figure 2.8 A schematic diagram of the pathways from the eyes to the visual cortex (from the IESNA Lighting Handbook)

The optic nerves leaving the two eyes are brought together at the optic chiasm where the nervesfrom each eye are split and parts from the same side of the two eyes are combined. Thisarrangement ensures that the signals from the same side of the two eyes are received togetheron the same side of the visual cortex. The pathways then proceed to the lateral geniculatenuclei. Somewhere between leaving the eyes and arriving at the lateral geniculate nuclei, someoptic nerve fibers are diverted to the superior colliculus, responsible for controlling eyemovements, and to the suprachiasmatic nucleus which is concerned with entraining circadianrhythms. After the lateral geniculate nuclei, the two optic nerves spread out to supplyinformation to various parts of the visual cortex, the part of the brain where vision occurs. The visual cortex is located at the back of cerebral hemispheres. About 80% of the cortical cells are devoted to the central ten degrees of the visual field, the centre of which is the fovea, a phenomenon that again emphasises the importance of the fovea.

2.1.7 Colour visionHuman colour vision is trichromatic. It is based on the L, M and S cone photoreceptors. Figure2.9 shows how the outputs from the three cone photoreceptor types are believed to be arranged.The achromatic channel combines inputs from the M- and L-cones only. Its output is related toluminance. The other two channels are opponent channels in that they produce a differencesignal. These opponent channels are responsible for the perception of colour. The red-greenopponent channel produces the difference between the output of the M-cones and the sum ofthe outputs of the L- and S-cones. The blue-yellow opponent channel produces the differencebetween the S-cones and the sum of the M- and L-cones.

2.1.6 The central visual pathwaysSignals from the retina are transmitted to the visual cortex of the brain over the centralvisual pathways (Figure 2.8).

Lateralgeniculate

nucleus

Visual cortexSuperiorcolliculus

Opticchiasm

Retina

Optictract

Opticnerve

Cortical cells


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Figure 2.9 The organisation of the human colour system showing how the three conephotoreceptor types are believed to feed into one achromatic, non-opponent channel and twochromatic, opponent channels (after Sekular and Blake, 1994)

The ability to discriminate the wavelength content of incident light makes a dramatic differenceto the information that can be extracted from a scene. Creatures with only one type ofphotopigment, i.e. creatures without colour vision, can only discriminate shades of grey, fromblack to white. Approximately 100 such discriminations can be made. Having three types ofphotopigment increases the number of discriminations to approximately 1,000,000. Thus, colourvision is a valuable part of the visual system, and not a luxury that adds little to utility.

2.2 Continuous adjustments of the visual system

2.2.1 AdaptationTo cope with the wide range of luminances to which it might be exposed, from a very dark night(10–6 cd/m2) to a sunlit beach (106 cd/m2), the visual system changes its sensitivity through aprocess called adaptation. Adaptation is a continuous process involving three distinct changes.

Change in pupil size: the iris constricts and dilates in response to increased and decreased levels ofretinal illumination. The maximum change in retinal illumination that can occur through pupilchanges is 16 to 1. As the visual system can operate over a range of about 1,000,000,000,000 to 1,this indicates that the pupil plays only a minor role in the adaptation of the visual system.

Neural adaptation: this is a fast (less than 200 ms) change in sensitivity produced in the retina.Neural processes account for virtually all the transitory changes in sensitivity of the eye atluminance values commonly encountered in electrically lighted environments, i.e. belowluminances of about 600 cd/m2. The facts that neural adaptation is fast, is operative at moderatelight levels, and is effective over a luminance range with a maximum to minimum ratio of 1000:1 explain why it is possible to look around most lit interiors without being conscious ofbeing misadapted.

S cones

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Photochemical adaptation: the sensitivity of the eye to light is largely a function of the percentage ofunbleached pigment in each photoreceptor. Under conditions of steady retinal illumination, theconcentration of photopigment produced by the competing processes of bleaching andregeneration is in equilibrium. When the retinal irradiance is changed, pigment is bleached andregenerated so as to re-establish equilibrium. Because the time required to accomplish thephotochemical reactions is of the order of minutes, changes in the sensitivity can lag behind theirradiance changes. The cone photoreceptors adapt much more rapidly than do the rodphotoreceptors. Exactly how long it takes to adapt to a change in retinal illumination depends onthe magnitude of the change, the extent to which it involves different photoreceptors and thedirection of the change. For changes in retinal illumination of about 2–3 log units, neuraladaptation is sufficient so adaptation should be complete in less than a second. For larger changesphotochemical adaptation is necessary. If the change in retinal illumination lies completelywithin the range of operation of the cone photoreceptors, a few minutes will be sufficient foradaptation to occur. If the change in retinal illumination covers from cone photoreceptoroperation to rod photoreceptor operation, tens of minutes may be necessary for adaptation to becompleted. As for the direction of change, once the photochemical processes are involved,changes to a higher retinal illuminance can be achieved much more rapidly than changes to alower retinal illuminance.

When the visual system is not completely adapted to the prevailing retinal illumination, itscapabilities are limited. This state of changing adaptation is called transient adaptation. Transientadaptation is unlikely to be noticeable in interiors in normal conditions but can be significantwhere sudden changes from high to low retinal illumination occur, such as on entering a longroad tunnel on a sunny day or in the event of a power failure in a windowless building.

2.2.2 Photopic, scotopic and mesopic visionThis process of adaptation can change the spectral sensitivity of the visual system because atdifferent retinal illuminances, different combinations of retinal photoreceptors are operating.The three states of sensitivity are conventionally identified as follows.

Photopic vision: this occurs at luminances higher than approximately 3 cd/m2. For theseluminances, the retinal response is dominated by the cone photoreceptors so both colour visionand fine resolution of detail are available.

Scotopic vision: this occurs at luminances less than approximately 0.001 cd/m2. For theseluminances only the rod photoreceptors respond to stimulation so colour is not perceived andthe fovea of the retina is blind.

Mesopic vision: this is intermediate between the photopic and scotopic states, i.e. between about0.001 cd/m2 and 3 cd/m2. In the mesopic state both cones and rod photoreceptors are active. Asluminance declines through the mesopic region, the fovea, which contains only conephotoreceptors, slowly declines in absolute sensitivity without significant change in spectralsensitivity, until vision fails altogether as the scotopic state is reached. In the periphery, the rodphotoreceptors gradually come to dominate the cone photoreceptors, resulting in gradualdeterioration in colour vision and resolution and a shift in spectral sensitivity to shorterwavelengths. The relevance of the different types of vision for lighting practice varies. Scotopicvision is largely irrelevant. Any lighting installation worthy of the name provides enough light toat least move the visual system into the mesopic state. Most interior lighting ensures the visualsystem is operating in the photopic state. Current practice in exterior lighting ensures the visualsystem is often operating in the mesopic state.


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All photometric quantities used by the lighting industry are based on the CIE Standard PhotopicObserver, i.e. photopic vision. Therefore, it should not come as a surprise when light sourceswith different spectral content do not have the same effects when used to provide mesopic visiondespite being matched photometrically.

2.2.3 AccommodationThere are three optical components involved in the ability of the eye to focus an image on theretina, the thin film of tears on the cornea, the cornea itself, and the crystalline lens. The ciliarymuscles have the ability to change the curvature of the lens and thereby adjust the power of theeye’s optical system in response to changing target distances; this change in optical power iscalled accommodation.

Accommodation is a continuous process, even when fixating, and is always a response to animage of the target located on or near the fovea rather than in the periphery of the retina. Anycondition that handicaps the fovea, such as a low light level, will adversely affect accommodativeability. As adaptation luminance decreases below 0.03 cd/m2, the range of accommodationnarrows so that it becomes increasingly difficult to focus objects near and far from the observer.When there is no stimulus for accommodation, as in complete darkness or in a uniformluminance visual field such as occurs in a dense fog, the visual system typically accommodates toapproximately 70 cm away.

2.3 Capabilities of the visual system

The human visual system has a limited range of capabilities. These limits, conventionally calledthresholds, are mainly of interest for determining what will not be seen rather than how wellsomething will be seen. For the threshold measurements shown here the observers were all fullyadapted, the target was presented on a field of uniform luminance and the observers’accommodation was correct.

2.3.1 Threshold measuresThe threshold capabilities of the human visual system can conveniently be divided into spatial,temporal and colour classes.

Spatial threshold measuresSpatial threshold measures relate to the ability to detect a target against a background or toresolve detail within a target. Common spatial threshold measures are threshold luminancecontrast and visual acuity.

The luminance contrast of a target quantifies its visibility relative to its immediate background.The higher is the luminance contrast, the easier it is to detect the target. There are threedifferent forms of luminance contrast. For uniform targets seen against a uniform background,luminance contrast is defined as

C =

where: C = luminance contrastLb = luminance of the backgroundLt = luminance of the target

Lt – LbLb


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This formula gives luminance contrasts which range from 0 to 1 for targets which have detailsdarker than the background and from 0 to infinity for targets which have details brighter thanthe background. It is widely used for the former, e.g. printed text on white paper.

Another form of luminance contrast for a uniform targets seen against a uniform background isdefined as

C = Lt / Lb

where: C = luminance contrastLb = luminance of the backgroundLt = luminance of the target

This formula gives luminance contrasts that can vary from 0, when the target has zeroluminance, to infinity, when the background has zero luminance. It is often used for self-luminous displays, e.g. computer monitors.

For targets that have a periodic luminance pattern, e.g. a grating, the luminance contrast is given by

C = (Lmax – Lmin) / (Lmax + Lmin)

where: C = luminance contrastLmax = maximum luminanceLmin = minimum luminance

This formula gives luminance contrasts that range from 0 to 1, regardless of the relativeluminances of the target and background. It is sometimes called the luminance modulation.

Given the different forms of luminance contrast measure, it is always important to understandwhich is being used.

Visual acuity is a measure of the ability to resolve detail for a target with a fixed luminancecontrast. Visual acuity is most meaningfully quantified as the angle subtended at the eye by thedetail that can be resolved on 50 percent of the occasions the target is presented. This angle isusually expressed in minutes of arc. Using this measure, the visual acuity corresponding to‘normal’ vision is taken to be 1 min arc. Unfortunately for simplicity, there are several othermeasures used to quantify visual acuity. One is the reciprocal of the angle subtended at the eyeby the detail that can be resolved on 50 percent of the occasions the target is presented. Arelative measure is used by the medical profession. This is the distance at which a patient canread a given size of letter or symbol relative to the distance an average member of thepopulation with normal vision could read the same letter or symbol. For example, if the patientis said to have 20/200 vision it means that the patient can only read a given letter at 20 feet thatan average member of the population with normal vision can read from 200 feet.

Again, given the different forms of visual acuity that are used by different professions, it isimportant to be sure which metric is being used.


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Temporal threshold measuresTemporal threshold measures relate to the speed of the response of the human visual system andits ability to detect fluctuations in luminance. The ability of the human visual system to detectfluctuations in luminance can be measured as the frequency of the fluctuation, in hertz, and theamplitude of the fluctuation, for the stimulus that can be detected on 50 percent of the occasionsit is presented. The amplitude is expressed as

M = (Lmax – Lmin) / (Lmax + Lmin)

where: M = modulationLmax = maximum luminanceLmin = minimum luminance

This formula gives modulations that range from 0 to 1. Sometimes, modulation is expressed as a percentage modulation, calculated by multiplying the modulation by 100.

Colour threshold measuresColour threshold measures are based on the separation in colour space of two colours that canjust be discriminated, usually measured on the CIE 1931 chromaticity diagram and the relateduniform chromaticity scale diagrams.

2.3.2 Factors determining visual thresholdThere are three distinct groups of factors that influence the measured threshold; visual systemfactors, target characteristics and the background against which the target appears.

Important visual system factors are the luminance to which the visual system is adapted, theposition in the visual field where the target appears, and the extent to which the eye is correctlyaccommodated. As a general rule, the lower the luminance to which the visual system is adapted,the further the target is from the fovea, and the more mismatched the accommodation of the eye is to the viewing distance, the larger will be the threshold values.

Important target characteristics are the size and luminance contrast of the target and the colourdifference between the target and the immediate background. All three factors interact. Forexample, the visual acuity for a low luminance contrast, achromatic target will be much largerthan for a high luminance contrast, achromatic target when expressed as minutes of arc but willbe reduced if there is a colour difference between the target and the background.

As for the effect of the background against which the target appears, the important factors are thearea, luminance and colour of the background. As a general rule, the larger the area around thetarget that is of a similar luminance to the target and neutral in colour, the smaller will be thethreshold measure.

2.3.3 Spatial thresholdsOne of the simplest visual tasks is the detection of a spot of light presented continuously against a uniform luminance background. For such a target the visual system demonstrates spatialsummation, i.e. the product of target luminance and target area is a constant. This relationshipbetween target luminance and target area is known as Ricco’s Law. It implies that the totalamount of energy required to stimulate the visual system so that the target can be detected is the same, regardless of whether it is concentrated in a small spot or distributed over a larger area.


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Figure 2.10 Threshold contrast plotted against background luminance for disc targets ofvarious diameters, viewed foveally. The discs were presented for 1 second (after Blackwell, 1959).

Spatial summation breaks down when the target is above about 6 min arc diameter for thefovea, above about 0.5 degree at 5 degrees from the fovea, and above about 2 degrees at 35 degrees from the fovea.

Given that the size of the target is above the critical size, the detection of the presence of a spotof light is determined simply by the luminance contrast. For the luminance of the surround inthe photopic range, there is a constant relationship between the luminance difference of thetarget and the background and the background luminance known as Weber’s Law. Thisrelationship takes the form

(Lt – Lb) / Lb = k

where: Lt = luminance of the targetLb = luminance of the backgroundk = constant

A more general picture of the effect of adaptation luminance on threshold contrast for targets of different size is shown in Figure 2.10. The increase in threshold contrast as adaptationluminance decreases is obvious, as is the increase in threshold contrast with decreasing targetsize. These data were obtained using a disc of different sizes presented for 1 second in thefovea. Decreasing the presentation time and moving the target away from the fovea increasesthe threshold contrast, for all sizes, particularly at lower adaptation luminances.

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Figure 2.11 Visual acuity, expressed as the reciprocal of the minimum gap size, for a Landoltring, plotted against log background luminance (after Shlaer, 1937)

2.3.4 Temporal thresholds The simplest possible form of temporal visual task is the detection of a spot of light brieflypresented against a uniform luminance background, i.e. a flash of light. For such a target thevisual system demonstrates temporal summation, i.e. the product of target luminance and theduration of the flash is a constant. This relationship between target luminance and duration isknown as Bloch’s Law. It implies that the total amount of energy required to stimulate thevisual system so that the target can be detected is the same, regardless of the time for which thetarget is presented. Temporal summation breaks down above a fixed duration, ranging from 0.1 s for scotopic luminances to 0.03 s for photopic luminances. For presentation times longerthan the critical duration, presentation time has no effect, the ability to detect the flash beingdetermined by the difference in luminance between the flash and the background.

Threshold luminance contrast is relevant to the detection of targets on a background. Targetswith a luminance contrast close to or below the threshold value are unlikely to be seen andtargets with a luminance contrast more than twice the threshold value are likely to be seenevery time.

Figure 2.11 shows the variation in visual acuity with luminance for foveal viewing of the target.As luminance increases, visual acuity, measured as the reciprocal of the minimum gap size,improves, approaching an asymptote at very high luminances corresponding to about 0.45 minarc. Visual acuity deteriorates with increasing deviation from the fovea and improves as the areaaround the target that has the same luminance increases.

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Figure 2.12 Critical fusion frequency plotted against log retinal illumination, for threedifferent test field sizes (after Hecht and Smith, 1936)

2.3.5 Colour thresholds Figure 2.13 shows the MacAdam ellipses, ten times enlarged, plotted in the CIE chromaticitydiagram. Each ellipse represents the standard deviation in the chromaticity coordinates forcolour matches made between the two parts of a 2–degree bipartite field with the reference fieldhaving the chromaticity of the centre point of the ellipse. The lighting industry uses four-stepMacAdam ellipses as its tolerance limits for quality control in lamp manufacture.

An aspect of temporal thresholds relevant to lighting is the ability to detect flicker. Figure 2.12shows the maximum frequency of a sinewave fluctuation at 100 percent modulation that isvisible at different retinal illuminations, for visual fields of different sizes. Retinal illuminationis measured in trolands which are the product of the luminance of the stimulus and theassociated pupil area. For large field sizes, such as might occur when using indirect lighting, the maximum frequency increases linearly with retinal illumination in the scotopic state, shows little change in the mesopic state and increases linearly in the photopic state until saturation occurs.

Critical fusionfrequency (Hz)

Log retinal illumination (trolands)

–3 –2 –1 0 1 2 3 4 5

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Figure 2.13 The CIE 1931 chromaticity diagram with the MacAdam ellipses displayed,multiplied ten times (after MacAdam, 1942, from the IESNA Lighting Handbook)

2.3.6 Light spectrum and movement Adaptation luminance and position relative to the fovea are major factors in determiningthresholds. Other factors, such as light spectrum and movement of the target are alsoimportant. Visual acuity is only slightly influenced by light spectrum, light sources with greaterenergy at short wavelengths enhance visual acuity. As for movement, as long as the movementis slow enough and smooth enough to allow the retinal image of the target to be kept on thefovea, visual acuity is only slightly worsened. However, smooth movements faster than 40 degrees per second or erratic movement at slower speeds will lead to a dramatic deterioration in visual acuity.

2.4 Suprathreshold performance

Threshold measurements are used to define whether or not a target will be seen. When thetarget can be seen every time, it is said to be suprathreshold and the question of interestbecomes how quickly and accurately the work of which the target is a part can be done. Theanswer to this question depends on the structure of the task. Most apparently visual tasksactually have three components; visual, cognitive and motor. The effect of lighting on taskperformance depends on the place of the visual component relative to the cognitive and motorcomponents. Tasks in which the visual component is large or limiting will be more sensitive tochanges in lighting conditions than tasks where the visual component is small or unimportant.

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Figure 2.14 Mean performance scores for Landolt ring charts of different critical size andcontrast, plotted against illuminance (after Weston, 1945)

It is important to distinguish between task performance and visual performance. Taskperformance is the performance of the whole task. Visual performance is the performance ofthe visual component of the task. Task performance is what is needed to measure productivityand estimate cost benefit ratios for lighting. Visual performance is all that lighting conditionscan influence directly. Every task has a different relationship between visual performance andtask performance depending on the structure of the task. This makes it impossible to generalisefrom measurements of visual performance to the performance of all tasks.

The impact of lighting conditions on visual performance is determined by the size, luminancecontrast and colour difference of the task and the amount, spectrum and distribution of thelighting. An analytical approach using a standard task measured over a wide range of conditionshas served to demonstrate, qualitatively, the effects of increasing illuminance on visualperformance (Figure 2.14). They are that increasing illuminance follows a law of diminishingreturns, i.e. that equal increments in illuminance lead to smaller and smaller changes in visualperformance until saturation occurs; that the point where saturation occurs is different fordifferent sizes and contrasts of critical detail; that larger improvements in visual performancecan be achieved by changing the task than by increasing the illuminance, at least over anyilluminance range of practical interest; and, that it is not possible to make a visually difficult taskreach the same level of performance as a visually easy task simply by increasing the illuminanceover any reasonable range.

10

Meanperformancescore

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Figure 2.15 The form of relative visual performance plotted against target luminance contrastand background luminance for a fixed target size (after Rea, 1986)

2.5 Visual search

One type of work that is outside the RVP model is visual search. Visual search proceeds via aseries of fixations joined together by saccades (Figure 2.2). This implies that the target is mostlikely to be seen first, away from the fovea. For a uniform field, where any departure fromuniformity is a target, the probability of off-axis detection can be related to the visibility of thedefect. The concept used to model the effect of lighting conditions on search time is the visualdetection lobe, i.e. a surface centred on the fovea that defines the probability of detecting thetarget at different deviations from the fovea within a single fixation pause (Figure 2.16).

While this understanding is useful, it is not enough to make quantitative predictions of the effectof lighting conditions on visual performance for all tasks although it is possible for some.Specifically, the relative visual performance (RVP) model of visual performance (Rea andOuellette, 1991) has been shown to make accurate predictions for tasks that are dominated by thevisual component, that do not require the use of peripheral vision to any extent, that presentstimuli to the visual system that can be completely characterised by their visual size, luminancecontrast and background luminance only, and that are seen in photopic conditions e.g. readingand doing data-entry work. Figure 2.15 shows the form of relative visual performance producedby this model for a fixed size but variable luminance contrast target and a range of backgroundluminances. This form has been described as the plateau and escarpment of visual performance,the point being that over a wide range of luminance contrasts and background luminances thechange in relative visual performance is slight but at some point either contrast or luminance willbe so low that performance will start to deteriorate rapidly. The objective of functional lighting isto keep performance on the plateau and well away from the escarpement.

Luminance (cd⋅m–2) Contrast

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Figure 2.16 The probability of detection of targets of (a) contrast = 0.058, size = 19 minarc; (b) contrast = 0.08, size = 10 min arc; (c) contrast = 0.044, size = 10 min arc; within asingle fixation pause, plotted against deviation from the visual axis. Each curve can be used toform a visual detection lobe for each target by assuming radial symmetry about the visual axis.

The visual detection lobe has a maximum at the fovea; the probability of detecting the targetdecreasing as the target is located further off-axis. Different targets have different visualdetection lobes. A large-area, high-contrast hole in some sheet material will have a large visualdetection lobe while a small-size, low-contrast hole will have a small lobe. The size of the visualdetection lobe matters because, provided the interfixation distance is related to it and the totalsearch area is fixed, the total time taken to cover the search area is inversely proportional to thesize of the visual detection lobe. Other important factors for determining visibility are theluminance contrast, and the colour of the target relative to the background.

There is also the question of what happens when the area to be searched contains other items.For searching uniform, empty fields, it is the visibility of the target off-axis that determines thesearch time. Where there are other items present, the visibility of the target alone is not enoughto predict the search time. The other factor that must be considered is the conspicuity of thetarget, i.e. how easy it is to distinguish the targets from the other items. For high conspicuity,the defects should differ from the other items in the field on as many dimensions as possible,e.g. size, contrast, shape, colour and movement.

Many of the lighting techniques used for visual search are aimed at either increasing the visualsize or luminance contrast of the defect, either by casting shadows (Figure 2.17) or by usingspecular reflections (Figure 2.18). Probably the most widely applicable aspect of lighting whichaids visual search is to increase the illuminance on the search area. While illuminance isgenerally a useful method of reducing search times, it should not be used without thought. Ifthe effect of increasing illuminance is to decrease the luminance contrast, or effective visual sizeof the targets or to produce confusing visual information in the search area, visual searchperformance will be worsened.

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Figure 2.17 A cut in textured material lit by directional lighting delivered at a glancing angleto the surface of the material. The cut is visible under the directional lighting because of thehigh luminance contrast. The high luminance contrast occurs because of the highlights on thesides of the cut and the deep shadow in the cut.

Figure 2.18 A specular aluminium surface with a cross scribed into it, lit by directionallighting from above and behind the camera. The scribed cross is easily seen because the scribedmarks cut into the surface and thereby alter the reflection characteristics of the surface. Theresult is a high luminance reflection towards the camera for the cut and a high luminancereflection away from the camera for the undamaged surface.


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2.6 Visual discomfort

There are four situations in which lighting installations may cause visual discomfort. They are:

visual task difficulty, in which the lighting makes the required information difficult to extract,

under- or over-stimulation, in which the visual environment is such that it presents too little or too much information,

distraction, in which the observer’s attention is drawn to objects that do not contain the information being sought,

perceptual confusion, in which the pattern of illuminance can be confused with the pattern of reflectance in the visual environment.

The occurrence of visual discomfort is made manifest by the occurrence of red, itchy eyes,headaches and aches and pains associated with poor posture. The most common aspects oflighting that cause visual discomfort are insufficient light, too much variation in illuminancebetween and across working surfaces, glare, veiling reflections, shadows and flicker.

2.6.1 Insufficient lightThere is insufficient light when the worker approaches the escarpment of the relative visualperformance surface for the task (see Figure 2.15). Behavioural signs that there is insufficientlight are attempts to move the work to get more light or movements by the worker to get closerto the task. Discomfort caused by insufficient light can be avoided by following therecommendations in the SLL Code for lighting and the guidance given in the application chaptersof this Handbook.

2.6.2 Illuminance uniformityLighting recommendations almost always include an illuminance uniformity criterion. These criteria can be direct or indirect. Direct criteria are ratios of illuminance, typicallyminimum/maximum or minimum/average measured on the relevant working plane. Indirectcriteria are selected to produce a minimum illuminance uniformity ratio, e.g. spacing/mountingheight ratio.

Such criteria can be considered on different scales. For a whole room where tasks can beanywhere in the room, the minimum/average illuminance ratio on the working plane shouldnot be less than 0.7. This criterion probably only applies where the lighting installation isperceived by the occupants to be intended to produce a uniform distribution of illuminance. Inrooms with large windows, the illuminance on a desk close to the window will be much greaterthan on a desk well back from the window so the illuminance uniformity ratio will be muchless than 0.7, but few complaints are heard. Similarly, studies in offices where the luminairescan be individually switched or dimmed have shown that wide variations in the illuminance ondesks can be tolerated, without complaint. This suggests that illuminance uniformity limitationsare more a design requirement adopted to ensure that no one has insufficient illuminance fortheir work rather than an intrinsic requirement of the visual system.

On the scale of an individual work surface, there are two potential sources of discomfort.Distraction can occur where there are areas of high illuminance adjacent to the work area.


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Perceptual confusion can occur when the illuminance pattern has a sharp edge so that it could bemistaken for a change in reflectance. The most preferred form of work surface lighting is one that provides a uniform illuminance over the area where the work is to be done(minimum/maximum illuminance ratio > 0.7) and lower illuminances outside that area.

2.6.3 GlareThe presence of a luminance much above the average for the visual field will produce discomfortand is called glare. There are five forms of glare associated with lighting installations.

Saturation glareThis occurs when a large part of the visual field is at a very high luminance for a long time, e.g.sunlight on snow. Saturation glare is painful and the behavioural response is to shield the eyes insome way, e.g. by wearing low transmittance glasses.

Adaptation glareThis occurs when the visual system is exposed to a sudden, large increase in luminance of thewhole visual field, e.g. on exiting a long road tunnel into bright sunlight. The perception of glareis due to the visual system being oversensitive. Adaptation glare is temporary in that visualadaptation will soon adjust the visual sensitivity to the new conditions. It can be avoided byproviding a transition zone of intermediate luminance, the transition zone being large enough toallow the visual system time to adapt to the new conditions.

Disability glareThis occurs when high luminance is present in a low luminance scene. Light from the source isscattered in the eye thereby forming a luminous veil over the retinal image of parts of the sceneadjacent to the source. This luminous veil reduces the luminance contrast and desaturates anycolours in the retinal image of the adjacent parts of the scene.

The magnitude of disability glare is quantified by the equivalent veiling luminance. For glaresources within an angular range of 0.1 to 30 degrees, this is given by the equation:

Lv = 10

where: Lv = equivalent veiling luminance (cd/m2)En = illuminance at the eye from the nth glare source (lx)Θn = angle of the nth glare source from the line of sight (degrees)

The effect of the equivalent veiling luminance on the luminance contrast of an object can beestimated by adding it to the luminance of both the object and the immediate background.

Disability glare can be associated with point sources and large area sources. The disability glareformulae can be applied directly to point sources but for large area sources, the area has to bebroken into small elements and the overall effect integrated. Disability glare from point sources is experienced most frequently on the roads at night when facing an oncoming vehicle. Disability glare from an extended source can occur when looking at an object on a wall adjacent to a window. The sky seen through the window is the glare source.

∑ En

Θ 2n


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Discomfort glareThis occurs when people complain about visual discomfort in the presence of bright lightsources, luminaires or windows. Discomfort glare is quantified by the Unified Glare Rating(UGR), derived from the equation:

UGR = 8 log10

where: UGR = Unified Glare RatingLb = background luminance (cd/m2), excluding the contribution of the glare sources.

This is numerically equal to the indirect illuminance on the plane of the observer’s eye, divided by π

Ls = luminance of the luminaire (cd/m2)ω = solid angle subtended at the observer’s eye by the luminaire (steradians)p = Guth position index

UGR values typically range from 13 to 30, the lower the value, the less the discomfort.Luminaire manufacturers publish UGR values for regular arrays of their luminaires in anumber of standardised rooms. This enables comparisons to be made between differentluminaire types. When making such a comparison the smallest meaningful difference is onewhole unit in UGR.

Where a luminous ceiling or uniform indirect lighting is used, discomfort glare is limited bysetting a maximum average illuminance. Specifically, if a UGR value of 13 is desired then theaverage illuminance provided should not exceed 300 lx, for UGR = 16, the maximum averageilluminance should not exceed 600 lx and for UGR = 19, the maximum average illuminanceshould not exceed 1,000 lx.

Overhead glareA high luminance immediately overhead can also cause discomfort, even though it cannot beseen when looking directly ahead. The cause of the discomfort is distraction, caused by highluminance reflections from eyebrows, glasses and facial features. The UGR system can beapplied to overhead glare to predict the magnitude of the discomfort.

2.6.4. Veiling reflectionsVeiling reflections are luminous reflections from specular surfaces that physically change thecontrast of the visual task and therefore change the stimulus presented to the visual system(Figure 2.19). The two factors that determine the nature and magnitude of veiling reflectionsare the specularity of the surface being viewed and the geometry between the observer, thesurface, and any sources of high luminance. If the surface is a perfectly diffuse reflector, noveiling reflections can occur. If the surface has a specular reflection component, veilingreflections can occur. Veiling reflections occur at positions where the geometry between theobserver, the surface and any sources of high luminance is such that the angle of incidencebetween the surface and the source of high luminance equals the angle of reflection betweenthe surface and the observer.

The effect of veiling reflections on the luminance contrast of a specific target may be quantifiedby adding the luminance of the veiling reflection to the appropriate components of theluminance contrast formulae. What the appropriate components are depends on the reflectionproperties of the material being viewed. For glossy ink writing on matte paper, the luminance ofthe veiling reflections should only be added to the luminance of the ink.

0.25Lb

∑ L ωp2

2s


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For a glossy magazine page or a VDT screen veiling reflections occur over the whole surface. Inthis case the luminance of the veiling reflections should be added to all terms in the luminancecontrast formula.

Figure 2.19 A glossy book, with and without veiling reflections

Although veiling reflections are usually considered a negative outcome of lighting that can cause discomfort, they can be used positively, but when they are, they are conventionally calledhighlights. Physically, veiling reflections and highlights are the same thing. Display lighting ofspecularly reflecting objects is all about producing highlights to reveal the specular nature of the surface.

2.6.5 ShadowsShadows are cast when light coming from a particular direction is intercepted by an opaque object.If the object is big enough, the effect is to reduce the illuminance over a large area. This is typicallythe problem in industrial lighting where large pieces of machinery cast shadows in adjacent areas.The effect of these shadows can be overcome either by increasing the proportion of inter-reflectedlight by using high reflectance surfaces or by providing local lighting in the shadowed area. If theobject is smaller, the shadow can be cast over a meaningful area which in turn can cause perceptualconfusion, particularly if the shadow moves. An example of this is the shadow of a hand cast on ablueprint. This problem can also be reduced by increasing the inter-reflected light in the space orby providing local lighting which can be adjusted in position.


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Although shadows can cause visual discomfort, it should be noted that they are also an essentialelement in revealing the form of three-dimensional objects. Techniques of display lighting arebased around the idea of creating highlights and shadows to change the perceived form of theobject being displayed. Many lighting designers insist that the distribution of shadows is asimportant as the distribution of light in achieving an attractive and meaningful visualenvironment.

The number and nature of shadows produced by a lighting installation depends on the size andnumber of light sources and the extent to which light is inter-reflected around the space. Thestrongest shadow is produced from a single point source in a black room. Weak shadows areproduced when the light sources are large in area and the degree of inter-reflection is high.

2.6.6 FlickerVirtually all electric light sources that operate from an alternating-current supply produceregular fluctuations in the amount of light emitted. When these fluctuations become visiblethey are called flicker.

The probability that a lighting installation will be seen to flicker can be minimised by ensuringa stable supply voltage and by the use of high-frequency electronic control gear for dischargelamps. Incandescent light sources do not require control gear but they are particularly sensitiveto fluctuations in supply voltage. Where the local electricity network has equipment attached toit that can impose sudden large loads, e.g. the motors of a steel rolling mill, local fluctuations insupply voltage are likely and, in consequence, so are fluctuations in light output of incandescentlight sources. These can be minimised by using a voltage regulator between the electricitysupply and the light source.

Discharge lamps are less sensitive to supply voltage fluctuations than incandescent lampsbecause the electricity supply is filtered through the control gear. Electromagnetic control geartypically produces an output at the same frequency as the electricity supply. Electronic controlgear for fluorescent lamps typically produces an output at much higher frequencies. Given thetime constants of the light producing processes in most discharge lamps, this increase in supplyfrequency not only produces a higher frequency but also a smaller percentage modulation inlight output.

Another approach used to reduce the probability of flicker is to combine light from lampspowered from different phases of the electricity supply on the working plane. This results in anincreased frequency and a reduced percentage modulation and hence a decrease in theprobability of flicker being seen when looking at the working plane. Obviously, it does nothingfor the probability of flicker being seen when looking directly at an individual light source.

Although flicker occurring over a large area is almost always disturbing, localised flicker doeshave its uses. Localised flicker is a potent means of attracting attention because peripheral visionis sensitive to changes in the retinal illumination pattern, either in space or time. Localisedflicker can also create a stroboscopic effect (see Section 10.2.8).

2.7 Perception through the visual system

2.7.1 The constanciesWhen considering how we perceive the world, the overwhelming impression is one of stabilityin the face of continuous variation. This invariance of perception is called perceptual constancy.


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There are four fundamental attributes of an object that are maintained constant over a wide rangeof lighting conditions.

Lightness: lightness is the perceptual attribute related to reflectance. In most lighting situations, itis possible to distinguish between the illuminance on a surface and its reflectance, i.e. to perceivethe difference between a low-reflectance surface receiving a high illuminance and a high-reflectance surface receiving a low illuminance, even when both surfaces have the sameluminance. It is this ability perceptually to separate the luminance of the retinal image into itscomponents of illuminance and reflectance that makes the use of luminance as the basis oflighting design criteria problematical.

Colour: physically, the stimulus a surface presents to the visual system depends on the spectralcontent of the light illuminating the surface and the spectral reflectance of the surface. However,quite large changes in the spectral content of the illuminant can be made without causing anychanges in the perceived colour of the surface, i.e. colour constancy occurs. Colour constancy issimilar in many ways to lightness constancy. There are two factors that need to be separated; thespectral distribution of the incident light and the spectral reflectance of the surface. As long as thespectral content of the incident light can be identified the spectral reflectance of the surface, andhence its colour, will be stable.

Size: as an object gets further away, the size of its retinal image gets smaller but the object itself isnot seen as getting smaller. This is because by using clues such as texture and masking, it isusually possible to estimate the distance and then to compensate unconsciously for the increasein distance.

Shape: as an object changes its orientation in space, its retinal image changes. Nonetheless, inmost lighting conditions the distribution of light and shade across the object makes it possible todetermine its orientation in space. This means that in most lighting conditions a circular platethat is tilted will continue to be seen as a tilted circular plate even though its retinal image is elliptical.

These constancies represent the application of everyday experience and the integration of all theinformation about the lighting available in the whole retinal image to the interpretation of a partof the retinal image that bears several alternative interpretations. Constancy is likely to breakdown whenever there is insufficient or misleading information available from the surroundingparts of the visual field. The constancies are most likely to be maintained when there is enoughlight for the observer to see the object and the surfaces around it clearly, the light being providedby an obvious but not necessarily visible light source, there are a variety of surface colours,including some small white surfaces and there are no large glossy areas. Lighting conditions usedin display lighting sometimes set out to break the constancies, particularly lightness constancy, inorder to give the display some drama.

2.7.2 Attributes and modes of appearanceWhile lighting has an important role in preserving or eliminating constancy, it also has a role indetermining the perceived visual attributes of objects. Objects can have five different attributes:brightness, lightness, hue, saturation, transparency and glossiness, depending on their nature andthe way they are lit. These attributes are defined as follows.

Brightness: an attribute based on the extent to which an object is judged to be emitting more or less light.


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Lightness: an attribute based on the extent to which an object is judged to be reflecting a greater orlesser fraction of the incident light.

Hue: an attribute based on the classification of a colour as reddish, yellowish, greenish, bluish ortheir intermediaries or as having no colour.

Saturation: an attribute based on the extent to which a colour is different from no colour of thesame brightness or lightness.

Transparency: an attribute based on the extent to which colours are seen behind or within an object.

Glossiness: an attribute based on the extent to which a surface is different from a matte surfacewith the same lightness, hue, saturation and transparency.

Not all these attributes occur in every situation. Rather, different combinations of attributesoccur in different modes of appearance. The four modes of appearance are as follows.

Aperture mode: this occurs when an object or surface has no definite location in space, as occurswhen a surface is viewed through an aperture.

Illuminant mode: this occurs when an object or surface is seen to be emitting light.

Object mode (volume): this occurs when a three-dimensional object has a definite location in spacewith defined boundaries.

Object mode (surface): this occurs when a two-dimensional surface has a definite location in spacewith defined boundaries.

Table 2.1 shows which of the attributes can be associated with each mode of appearance. Ofparticular interest to the perception of lighting is the shift between the attributes of brightnessand lightness in different modes of appearance. An object which appears in the self-luminousmode, such as a VDT screen or a light source, is perceived to have a brightness but not alightness. In this mode of appearance, the concept of reflectance is perceptually meaningless.However, an object that appears in the volume mode, such as a VDT screen or a light source that is turned off, does not have an attribute of brightness but does have a lightness in that itsreflectance can be estimated.

Table 2.1 The visual attributes that can occur with each mode of appearance

Attribute

Brightness

Lightness

Hue

Saturation

Transparency

Glossiness

Aperture

*

*

*

Illuminant

*

*

*

*

Volume

*

*

*

*

Surface

*

*

*

*

*


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A similar transformation occurs between the volume or surface modes of appearance and theaperture mode. Even non-self-luminous objects seen in the aperture mode are perceived ashaving a brightness but not a lightness. When seen in the object mode they have a lightness butnot a brightness. This is important because lighting can be used to change the mode ofappearance. For example, a painting hung on a wall has a lightness attribute when lighted sothat both it and the wall appear in the object mode (surface). However, if the painting isilluminated solely with a carefully aimed framing spot so that the edge of the beam coincideswith the edges of the painting, the painting is seen in the aperture mode and takes on a self-luminous quality with a brightness attribute. Adjusting the modes of appearance is an importanttechnique in display lighting, both indoors and outdoors.

2.8 Anomolies of vision

All the capabilities of human vision discussed above assume normal vision. However, there area number of forms of defective vision that occur due to either genetics or ageing.

2.8.1 Defective colour visionAbout 8 percent of males and 0.4 percent of females have some form of defective colour vision.People with defective colour vision are classified into three categories: monochromats,dichromats, and anomalous trichromats, according to the number of photoreceptors presentand the nature of the photopigments present in the photoreceptors.

Monochromats, although very rare, occur in two forms: rod monochromats, where there are nocone photoreceptors, only rod photoreceptors; and cone monochromats, where there are rodphotoreceptors and only one type of cone photoreceptor, usually the short-wavelength cone.Rod monochromats are truly colour-blind and see only differences in brightness. Conemonochromats have a very limited form of colour vision in the luminance range where bothrod and short-wavelength cones are operating.

Dichromats have two cone photoreceptors. They see a more limited range of colours thanpeople with normal colour vision and have a different spectral sensitivity, depending on whichcone photoreceptor is missing. Dichromats with the long-wavelength cone missing are calledprotanopes. Dichromats with the medium-wavelength cone missing are called deuteranopes,while dichromats with short-wavelength cones missing are called tritanopes.

Anomalous trichromats have all three cone photopigments present, but one of the conescontains a photopigment that does not have the usual spectral sensitivity. Anomaloustrichromats who have a defective long-wavelength photopigment are called protonamalous.Anomalous trichromats who have a defective medium-wavelength photopigment are calleddeteuranomalous, while anomalous trichromats who have a defective short-wavelengthphotopigment are called tritanomalous. The colour vision of anomalous trichromats can varywidely from almost as bad as a dichromat to little different from someone with normal colour vision.

People with defective colour vision have trouble with some everyday tasks (see Table 2.2) andare prohibited from some occupations. Defective colour vision is usually inherited, although itcan also be acquired through age, disease, injury or exposure to some chemicals.


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Table 2.2 Percentage of people with different types of colour vision reporting difficulties witheveryday tasks (from Steward and Cole, 1989)

2.8.2 Low visionAs the visual system ages, the ability to focus close up is diminished, the amount of lightreaching the retina is reduced, more of the light reaching the retina is scattered, the spectrum ofthe light reaching the retina is changed and more straylight is generated inside the eye. Thesechanges start in early adulthood and continue at a steady rate with increasing age. Theconsequences of these changes with age for the capabilities of the visual system are many andvaried. At the threshold level, old age is characterised by reduced absolute sensitivity to light,reduced visual acuity, increased contrast threshold, reduced colour discrimination and greatersensitivity to glare. In practice, the elderly have difficulty seeing in dim light, moving frombright to dark conditions suddenly, reading small print and distinguishing dark colours.

With increasing age comes a greater likelihood of pathological changes leading to low vision andeventual blindness. The World Health organisation (WHO) defines classes of vision based onvisual acuity and visual field size (Table 2.3).

Activity

Selecting clothes, cosmetics etc.

Distinguishing the colours of wires, paints etc.

Identifying plants and flowers

Determining when fruits andvegetables are ripe, by colour

Determining when meat is cooked, by colour

Difficulties in participating or watching sports, because of colour

Adjusting the colour balance of a television satisfactorily

Recognising skin conditions such as a rash or sunburn

Taking the wrong medication because of difficulties with colour

Dichromats

86

68

57

41

35

32

27

27

0

Anomaloustrichromats

66

23

18

22

17

18

18

11

3

Normal

0

0

0

0

0

0

2

0

0


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The prevalence of low vision and blindness increases dramatically after 70 years of age (Table2.4) The four most common causes of low vision in developed countries are cataract, maculardegeneration, glaucoma and diabetic retinopathy.

Table 2.4 Percentage prevalence of blindness and low vision for different age groups andraces. In this case, blindness is defined as a visual acuity of 20/200 or worse, and low vision isdefined as a visual acuity of from 20/40 to 20/200 (after Tielsch et al, 1990)

Cataract is an opacity developing in the lens. The effect of cataract is to absorb and scatter morelight on passage through the lens. This results in reduced visual acuity and increased contrastthresholds over the entire visual field, as well as greater sensitivity to glare.

Macular degeneration occurs when the macular, which covers the fovea, becomes opaque. Anopacity immediately in front of the fovea implies a serious reduction in foveal vision so seeingdetail becomes difficult if not impossible. However, peripheral vision is unaffected so the abilityto orient oneself in space and to find ones way around is little changed.

Table 2.3 The WHO classification of vision (after Tielsch et al, 1990)

Category

Normal vision

Near normal vision

Low vision

Moderate visual impairment

Severe visual impairment

Blindness

Profound visual impairment

Near-total visual impairment

Total visual impairment

Grade

0

0

1

2

3

4

5

Criteria

20/25 or better

20/30 to 20/60

20/70 to 20/160

20/200 to 20/400

20/500 to 20/1000 or a visual field less than 10°

Worse than 20/1000 or a visual field less than 5°

No light perception

Age range (years)

40–49

50–59

60–69

70–79

80+

Blindness(Caucasian)

0.6

0.5

0.2

0.6

7.3

Blindness(Afro-American)

0.6

0.7

1.6

2.9

8.0

Low vision(Caucasian)

0.2

0.7

1.1

5.2

14.6

Low vision(Afro-American)

0.6

1.3

3.4

8.1

18.0


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Glaucoma is shown by a progressive narrowing of the visual field. Glaucoma is due to anincrease in intraocular pressure which damages the blood vessels supplying the retina.Glaucoma will continue until complete blindness occurs unless the intraocular pressure is reduced.

Diabetic retinopathy is a consequence of chronic diabetes mellitus and effectively destroys partsof the retina. The effect this has on visual capabilities depends on where on the retina thedamage occurs and the rate at which it progresses.

These changes with age can be compensated, to some extent. The limited range of focus of theelderly can be overcome by the use of lenses. The tasks they have difficulty with can beredesigned to make them visually easier, usually by increasing the luminance contrast of thetask details, making the task details bigger and using more saturated colours. Lighting can alsobe used to compensate for aging vision. The elderly benefit more from higher illuminancesthan do the young, but simply providing more light may not be enough. The light has to beprovided in such a way that both disability and discomfort glare are carefully controlled andveiling reflections are avoided. Where elderly people are likely to be moving from a well-lit areato a dark area a transition zone with a gradually reducing illuminance is desirable.

People with low vision may or may not benefit from such changes in lighting depending on thespecific cause of the low vision. However, there is one approach that is generally useful. Thisapproach is to simplify the visual environment and to make its salient details more visible byattaching high luminance contrast to those details, and only to those details. Figure 2.20 showsan interior where this principle has been applied.

Figure 2.20 Contrast in the visual environment


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PART 2. TECHNOLOGY

Chapter 3: Light sources

3.1 Production of radiation

3.1.1 IncandescenceWhen an object is heated to a high temperature, the atoms within the material become excitedby the many interactions between them and energy is radiated in a continuous spectrum. Theexact nature of the radiation produced by an idealised radiator, known as a black body, wasstudied by Max Planck at the end of the 19th century and he developed the following formulato predict the radiation produced

where: is the spectral radiant exitance, c1 and c2 are constants, with values of 3.742 × 10–16 W/m2 and 1.439 × 10–2 m⋅K respectively. λ is the wavelength in metresT the temperature in kelvins.

The values of the spectral radiant exitance are plotted for different temperatures in Figure 3.1.

M theλ =

c1

λ5 [exp(c2/ λT) –1]

M theλ

Wien’s Displacement Law

4500

T (K)4000

3500

3000

2500

2000

20 × 106

15 × 106

10 × 106

5 × 106

20 × 106

Wavelength (nm)

th eλSp

ectr

alra

dia

nt

exci

tan

ceM

(W⋅m

–2p

erµm

wav

eban

d)

λmax

Figure 3.1 Spectral power distribution of radiation according to Planck’s Law

500 1000 1500


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The wavelength for maximum power (λmax) is inversely proportional to the temperature (T).The following formula was developed by Planck’s co-worker at the University of Berlin and isknown as Wien’s Displacement Law.

c3 has a value of 2.90 × 10–3 mK.

The result of the application of this formula is that if an object is heated to a high enoughtemperature (in excess of 2,000 ˚C) a reasonable amount of light is produced; this provides thebasic operating principle of the incandescent lamp.

In practice many materials when heated radiate energy at slightly different rates to thatpredicted by Planck. This property can be exploited by light source makers. For exampletungsten emits about a third more energy as light than would be predicted by Planck’s formula.

3.1.2 Electric discharges An electric discharge is an electric current that flows through a gas. These discharges generallytake a high voltage to initiate but once started they can carry considerable currents with verylittle voltage drop. A good example of such a discharge is the natural phenomenon of lightning. In an electric discharge the electric current is carried by electrons that have been removed fromthe gas atoms and ions that are gas atoms with one or more electrons removed. This is shownin Figure 3.2.

++++

Figure 3.2 Electric discharge through an ionised gas

The negatively charged electrons tend to drift towards the anode whilst the positively chargedions drift towards the cathode. As the ions are several thousand times heavier than the electronsthey tend to be less mobile.

When an electron collides with an atom, one of three things may happen:

(a) The electron rebounds with only a small change in energy – elastic collision(b) The impact excites the atom and the electron loses energy – excitation(c) The impact removes an electron from the atom – ionisation

Elastic collisions just heat the gas. Excitation raises the energy state of the atom so that it mayradiate light. Ionisation generates more free electrons so that the discharge is maintained.

λmax =c3

T

Electron

Positive Ion Anode

Current direction

Cathode


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Figure 3.3 Simplified energy level and transition diagram for mercury

The result of any collision between an electron and an atom is largely dependent on the energy of the electron. If the energy of the electron is less than that necessary to raise the atom to thefirst excited state then the collision will be elastic.

The most common transition is between the ground state of the atom and the first excited state.Radiation from the atom returning to ground state tends to dominate the output of thedischarge; this radiation is known as resonance radiation.

In low pressure discharges, such as low pressure sodium, the light output tends to be at a seriesof discrete wavelengths, each corresponding to a particular energy transition in the atoms of thegas. In high pressure discharges the atoms of the gas interact with one another and this coupledwith the higher electric and magnetic fields in the discharge cause the individual wavelengthsfound in the low pressure discharge to broaden into wider bands of radiation output. Indeveloping lamps the selection of atoms or molecules that have energy transitions thatcorrespond to radiation in the visible and ultra-violet is important (Figure 3.3).

Starting a discharge can be difficult because if there are no ions and free electrons present, thegas will not conduct a current. Most lamps use either a high voltage pulse or heated electrodescovered in special powders to get started.

The electrical properties of the discharge are unusual and in general discharges do not obeyOhm’s Law. This is because the current in a discharge is carried by electrons and ions and theirnumber is generally a function of the current, thus at higher currents it is easier for the chargeto pass through the discharge and the voltage drops. In order to maintain a steady currentthrough a lamp most discharge lamps require control gear.

Ionisation Excitation Radiation

Ion

Green546.1

Blue435.8

Violet404.7 nm

Excitedstates

Ultravioletresonanceradiation253.7 nm

Groundstate

10.43

7.73

5.46

4.894.67En

erg

y(e

lect

ron

volt

s)


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3.1.3 ElectroluminescenceSome materials will convert electricity into light directly. Two major physical processes accountfor the majority of the various electroluminescence phenomena. They are the recombination of current carriers in certain semi-conductors and via the excitation of luminescent centres incertain phosphors.

Pure semi-conductors have intrinsically a very high resistivity and it is only when they aredoped with other materials that it is possible to pass electricity through them. Some materialsinduce conduction by negatively charged carriers (n-type) and some by positively chargedcarriers (p-type). When charged carriers of different types recombine the energy released maybe emitted as light. See section 3.3.9 for more information on light emitting diodes.

Some phosphors can be excited by electrical fields (usually an alternating field) to produce light.The most common material used is zinc sulphide generally doped with another metal such ascopper. The process by which the radiation is created is not fully understood. However this hasnot stopped the process being used to make self luminous signs. For more information onelectroluminescent light sources see section 3.3.10.

3.1.4 LuminescenceThe term luminescence is sometimes also known as fluorescence, or photoluminescence. Theprocess involves a material absorbing radiation and then re-emitting light. The energy may bere-radiated almost immediately or it may take several hours. There are a number of ways thatthe material can hold the energy and this impacts on length of the time the energy is stored andthe amount of energy that is re-radiated.

Figure 3.4 Simplified representations of energy level schemes in luminescence

In Figure 3.4 image (a) represents simple luminescence where the material absorbs the energyand the next transition is to re-radiate the energy. In (b) the some of energy in the material islost via another process before re-radiation takes place. In (c) some of the energy is dissipatedand the material falls into a state where it can not re-radiate until it is restored to the higherenergy level. This process can lock energy into materials and is the basis of some ‘glow in thedark’ materials.

3.1.5 RadioluminescenceThis occurs in a similar manner to luminescence but the primary source of the activationenergy is particles or gamma rays emitted by a decaying nucleus of a radioactive atom.

a b c


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3.1.6 CathodoluminescenceIn cathodoluminescence the energy driving the phosphor is an electron that has been acceleratedaway from a cathode. This process is the means by which light is generated in a cathode ray tube.

3.1.7 ChemiluminescenceSome chemical reactions can produce light directly, not via the heat the reaction creates. Theprocess is used by some living organisms to generate light; the best known example being theglow worm.

3.1.8 ThermoluminescenceThis is exhibited by some materials when they are heated. The materials give out much morelight than would be expected due to black body radiation. The best known practical use of themethod of light production is the mantle used in some types of gas lamps.

3.2 Daylight

The sun is a large cloud of high temperature hydrogen gas. It is held together by its owngravitational force. As the atoms of hydrogen are held together at such pressure and hightemperature it is possible for nuclear fusion to take place and the hydrogen is converted intoheavier elements, mainly helium. This process releases a lot of energy which keeps the sun hot;because the sun is so hot it radiates energy by incandescence.

The sun is the biggest source of light on earth. Light from the sun not only gives us light so thatwe can see, it also powers the whole ecosystem on earth. Light from the sun can reach the earthin two ways: directly as sunlight, and, after it has been modified and redistributed by theatmosphere, as skylight.

3.2.1 SunlightThe key to the understanding of sunlight is knowing where the sun will be in the sky at any given time or date relative to the site in question.

On any given day the sun will rise in the east. In the northern hemisphere the sun then risesthrough the southern sky; reaching its highest altitude at due south at solar noon and passesthrough the southern sky before setting in the west.

Figure 3.5 The daily sun path

S N

W

E


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At different times of the year the sun follows different paths in the sky (Figure 3.6). The angleof inclination of the path of the sun from the perpendicular is equal to the latitude of the site.

Figure 3.6 Annual variations in the sun path

To understand the reasons behind these sun paths and to be able to predict the position of thesun at any time it is necessary to consider the relative motions of the sun and the earth. Theearth rotates on its axis in approximately 23 hours and 56 minutes and it orbits the sun once peryear. The reason that days last approximately 24 hours is that due to its motion around the sun,the earth has to turn a little bit more than one rotation before the same point on its surface isfacing the sun again. The orbit of the of the earth around the sun is shown in Figure 3.7.

Figure 3.7 Orbit of the earth around the sun

S N

W

E

Summer solstice

Equinox

Winter solstice

December

September

SunJune

March

23˚ 27’


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Figure 3.8 Angular co-ordinates used to describe the sun’s position

There are formulae available to calculate the position of the sun at any time and any date, howevercare needs to be used in the calculations as they rely on inverse trigonometric functions and it isquite easy to confuse the results as most of the functions may take the same value for more thanone angle.

3.2.2 SkylightWhilst equations mentioned in the previous section can predict the position of the sun in the sky,they tell us very little about the distribution of light throughout the sky. This is because the light from the sun is scattered by the atmosphere, and the distribution and amount of light received atground level is dependent on atmospheric conditions.

To calculate the distribution of luminance under various atmospheric conditions the standard BS EN 15469: 2004: Spatial distribution of daylight — CIE standard general sky may be used. This lists a series of 15 sky distributions and gives a formula that may be used for calculating the relativeluminance distribution of the sky.

The tilt of the earth’s axis away from the normal to the plane of the orbit is what causes theseasonal variation in the sun path. The angle that the sun makes to the earth normal to theequator is known as the angle of declination.

To be able to predict the sun’s position in the sky it is first necessary to define a system ofangular co-ordinates by which the sun’s position may be described.

NS

E

W

a

g


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Type Number

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

Description of luminance distribution

CIE Standard Overcast Sky, steep luminance gradation towards zenith, azimuthal uniformity

Overcast, with steep luminance gradation and slight brightening towards the sun

Overcast, moderately graded with azimuthal uniformity

Overcast, moderately graded and slight brightening towards the sun

Sky of uniform luminance

Partly cloudy sky, no gradation towards zenith, slight brightening towards the sun

Partly cloudy sky, no gradation towards zenith, brighter circumsolar region

Partly cloudy sky, no gradation towards zenith, distinct solar corona

Partly cloudy, with the obscured sun

Partly cloudy, with brighter circumsolar region

White-blue sky with distinct solar corona

CIE Standard Clear Sky, low luminance turbidity

CIE Standard Clear Sky, polluted atmosphere

Cloudless turbid sky with broad solar corona

White-blue turbid sky with broad solar corona

The standard helps with the distribution of daylight but it gives no information on the actualamount of daylight available at any particular time. There are a number of stations that recordthe global and diffuse (not including light direct from the sun) horizontal plane illuminancevalues on an unobstructed site and these data can be used to predict daylight availability.

Whilst data are logged every five minutes or so at most measuring stations it is usuallypresented as a chart showing monthly averages of hourly values. Figure 3.9 shows a typical chart giving data on daylight availability.

Table 3.1 CIE standard sky types


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Figure 3.9 A typical daylight availability chart

The colour of the light from the sun and sky depends not only on the colour of the light fromthe sun but also on the way that light is absorbed and scattered by the atmosphere.

300

Wavelength (nm)

350 400 450 500 550 600 650 700 750 800 850

Figure 3.10 The spectrum of daylight with a colour temperature of 6500 K (from CIEPublication 15.2)

Figure 3.10 shows the standardised spectrum of daylight from the CIE Publication 15.2 whichgives formulae for the calculation of daylight spectra of different colour temperatures. Inpractice the sky condition is constantly changing so it is difficult to give exact values of thecolour of the sky, however, Table 3.2 lists approximate values of correlated colour temperaturefor various sky conditions.

Time of year

24

18

12

6

0

5 klx

10 klx

20 klx

35 klx

Winter

1 klx = 1000 lux

Tim

eo

fd

ay(G

MT)

WinterSpring Summer Autumn


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Sky condition

Bright midday sun

Lightly overcast sky

Heavily overcast sky

Hazy sky

Deep blue clear sky

CCT (K)

5,200

6,000

6,500

8,000

20,000

3.3 Electric light

3.3.1 IncandescentThe incandescent lamp is operated by heating a filament in the lamp to a high temperature, sothat it emits light. The basic principle of the lamp may be simple but the technology required tomaintain a filament at a high enough temperature to give significant amount of light whilstensuring the lamp has a reasonable life is highly complex. The basic and most popular form ofthe lamp is the General Lighting Service (GLS) lamp.

Figure 3.11 The constructionof a GLSincandescent lamp

Glass bulb

Tungsten filament

Lead wire

Molybdenum filament supports

Dumet wire

Glass pinch

Balotini filled fuse sleeve

Exhaust tube

Fuse

Cement

Lead wire

Cap

Contacts

Table 3.2 Correlated colour temperatures of the sky


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The filament design is critical in setting up the operating characteristics of the lamp. The lengthof the filament wire is largely determined by the supply voltage, whilst the thickness of the wireis determined by the operating current of the lamp. The filament is coiled to reduce heatconvection to the filling gas. There are various forms of filament coiling with the coiled coilbeing one of the most common (see Figure 3.12).

Figure 3.12 A coiled coil filament

The filament must be robust enough to withstand the shocks and vibration that the lamp receivesduring its life and at the same time be rigid enough so that it does not droop. Support wires canhelp prevent the filament from drooping but they conduct heat away from the filament and thusreduce the efficiency of the lamp. Therefore normal service lamps are made with hard brittlefilaments that only need a few support wires. Lamps for rough service are made with a softermore malleable filament but have several support wires.

The bulb is generally made of a soft soda glass and its size is set so that it does not get too hot andthe tungsten that evaporates from the filament during the life of the lamp does not blacken thebulb too much.

The gas filling of the lamp is present to reduce the rate at which the tungsten evaporates and thusmake the lamp last longer. To minimise the heat losses from the filament noble gasses are used asthe primary fill gases. Most lamps have argon based filling but some high performance lamps usekrypton. In addition to the noble gas filling most mains voltage lamps have a small percentage ofnitrogen added to the filling to help suppress arcing at the end of life.

There are many variations on this basic lamp type. They are designed to run on voltages between1.5 and 415 volts at wattages between 1 and 1,000 watts. There is also a wide variety of bulbshapes including lamps with built in reflectors.

Figure 3.13 Forms of incandescent lamp


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3.3.2 Tungsten halogenThe applications of conventional incandescent lamps are limited by their physical size andluminous efficiency. Raising the filament temperature to increase the luminous output has theeffect of increasing the rate of blackening of the glass envelope, blackening which is a result ofthe evaporation of tungsten from the filament. By adding a halogen to the gas fill a chemicaltransport cycle involving the reaction of tungsten reduces the amount of blackening of theenvelope. It is then possible to reduce the size of lamp, increase the pressure of the filling gasand thereby limit the loss of the tungsten from the filament.

Figure 3.14 A representation of the tungsten halogen cycle

The chemistry of the tungsten halogen cycle is highly complex. However the key stages are:

the halogen combining with the tungsten on the wall of the lamp (zone 3)

the tungsten halide vapour mixing with the fill gas of the lamp (zone 2)

the tungsten halide dissociating close to the filament of the lamp, leaving the halogen free to migrate though the fill gas to the lamp wall again and the tungsten being deposited on the filament (zone 1).

To enable an efficient cycle it is necessary for the wall of the lamp to run at a temperature above 250 ˚C; this means that the bulb has to be made from quartz or hard glass.

Tungsten filament

Zone 1 Zone 2 Zone 3

Filament support

Fil seal 350 ˚C maximum

Ceramic

Lamp wall temperature250 ˚C minimum


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Figure 3.15 Forms of tungsten halogen lamps

Tungsten halogen lamps are more efficient and have longer lives compared with standardtungsten lamps. Also they are more compact than standard lamps. However they are moreexpensive as it is hard to make the quartz outer bulb and it is harder to introduce the gas fillinto the lamp due to the high filling pressure.

3.3.3 FluorescentFluorescent lamps are the most commonly used form of discharge lamp. They come in avariety of shapes and sizes and are available in a wide range of colours. The original form of thelamp was a long straight tube. New forms of the lamp known as compact fluorescent lampshave been developed where the lamp tube is bent or folded to produce a smaller light source.

Fluorescent lamps work by generating ultraviolet radiation in a discharge in low pressuremercury vapour. This is then converted into visible light by a phosphor coating on the inside ofthe tube. The electric current supplied to the discharge has to be limited by control gear tomaintain stable operation of the lamp. Traditionally this is done with magnetic chokes but mostcircuits now use high frequency electronic control gear. Electronic control gear has a number ofadvantages: first, driving the lamp at high frequency maintains the ions in the gas and thusmakes the lamp run more efficiently. Secondly, it reduces the amount of flicker in the lamp and,finally, electronic gear consumes less power than a magnetic choke.

Figure 3.16 Working principle of a fluorescent lamp

Ultraviolet radiation

Fluorescent powder Mercury atom Electrons Electrode

Visible radiation


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The lamps are made from the following main components.

The tube: this is made from a glass with a high iron content so that any short wave UV radiationthat gets through the phosphor coating is absorbed by the glass

The phosphor coating: there are a wide variety of phosphors available. Each produces a differentspectrum of light and by careful blending of the various phosphors lamp makers can tailor a widerange of lamp colours. The lumen output of the lamp also depends on the choice of phosphormix. It is also important to control the particle size of the phosphor powders and the thickness ofthe coating.

There are three main types of phosphor mixes currently used in fluorescent lamps:

Halophosphates: this range of phosphors tend to emit light in a relatively wide band and it is normal to use only one phosphor of this type at any one time. Halophosphates are only reasonably efficient as phosphors and generally have poor colour rendering.

Tri-phosphors: are mixes of three narrow band phosphors. They generally achieve CIE general colour rendering indices greater than 80 and have a high efficacy and good lumen maintenance.

Multi-phosphors: are mixes of a number, usually five, phosphors. These mixes usually give a CIE general colour rending index higher than 90, however the efficacy is normally lower than a tri-phosphor mix.

The electrodes: generally coils of tungsten wire that are coated in a material that when heated willgive off electrons readily. To start the lamp a current is passed through the coil to heat theemissive coating. However, once the lamp is running the ionised gas atoms hitting the electrodeprovide enough energy to keep the cathode hot. The electrodes are generally surrounded by ashield as some of the material used to coat the electrode evaporates during the life of the lamp. If the shield was not there the material would be deposited on the wall of the lamp causing ablack ring and reducing the light output.

The gas fill: the lamp fill is made up of two components; a noble gas mixture and the mercuryvapour. The noble gas in the lamp has three main functions. First, it reduces the mobility of thefree electrons in the lamp and by careful control of the pressure; it optimises the number ofelectrons with the right amount of energy to excite the mercury atoms.

Secondly, the gas reduces the rate at which the coatings on the electrodes evaporate and thusprolongs the life of the lamp. Finally it lowers the breakdown voltage of the lamp and thus makesstarting easier. Most lamps use either a mixture of argon and krypton or neon and argon. The useof the heaver krypton gas makes the lamps slightly more efficient but it is significantly moreexpensive. The vapour pressure of mercury in the lamp is significantly lower than the pressure ofthe noble gas mixture and it is controlled by the temperature of the coolest part of the lamp. Atthe cold spot of the lamp the mercury condenses to form liquid mercury. At this point the liquidand gaseous mercury are in equilibrium and the vapour pressure is determined by thetemperature. As the vapour pressure of mercury is critical to the operation of the lamp, the lightoutput of the lamp varies with temperature. Most lamps are optimised to run in an environmentwith an ambient temperature of 25 ˚C.


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However, some of the new types of lamp are set up to run in an ambient temperature of 35 ˚C. In some lamp types the mercury dose is mixed with other metals such as bismuth orindium. These metals form an amalgam with the mercury and this reduces the vapour pressureof the mercury at any given temperature. This enables the lamp to operate at highertemperatures but has the drawback that the lamp takes a long time to reach full output.

Figure 3.17 Luminous flux as a function of temperature for standard and amalgamfluorescent lamps. 100 percent corresponds to the maximum luminous flux.

There are two main types of fluorescent lamps; the traditional linear lamps and the compactfluorescent lamps.

Linear lamps come in variety of diameters and lengths. The main diameters of lamp are the T12lamps which are 38 mm in diameter, T8 lamps which are 25 mm and the T5 types which are 16 mm. All of these families of lamps come in a variety of lengths and wattages. Linearfluorescent lamps are generally efficient light sources with some of the lamps approaching 100 lumens per watt. They also come in a wide variety of colours with a range of colourrendering properties. Table 3.3 gives a summary of the main lamp colours.

100

90

80

70

60

50

Ambient temperature (˚C )

Rel

ativ

elu

min

ou

sfl

ux

(%)

10 20 30 40 50 60 70 80

Amalgam lamps

Standard lamps


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There is a large variety of compact fluorescent lamp types. Figure 3.18 below illustrates the range.

Figure 3.18 Types of compact fluorescent lamp

Colourappearance

Northlight(6000–6500 K)

Daylight(5000–5500 K)

Cool White

(4000 K)

Intermediate(3500 K)

White

Warm White(3000 K)

Very Warm(2700 K)

Multi-phosphorcolour rendering group 1a

Colour 965

Colour 950Lumilux De Luxe 950


Polylux Deluxe 940


Polylux Deluxe 930

Triphosphor colour rendering group 1b

Colour 865Lumilux Plus ECO 860Luxline Plus ECO 860

Polylux XLR 860


Polylux XLR 840


Polylux XLR 835


Polylux XLR 830


Polylux XLR 827

Quad-lamp Triple-twin

Twin-tube

2-D

HelicalCircline Oct lamp

F-lamp

Table 3.3 Colours of fluorescent lamps


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In general compact fluorescent lamps are less efficient than linear lamps, but because of theirsmall size, they are suited to many applications where a smaller lamp is needed. Some of thelamps have the control gear built into them and can be retro-fitted into GLS lamp sockets.

3.3.4 High pressure mercuryIn this type of lamp a discharge takes place in a quartz discharge tube containing mercuryvapour at high pressure (2 to 10 atmospheres). Some of the radiation from the discharge occursin the visible spectrum but part of the radiation is emitted in the ultraviolet. The outer bulb ofthe lamp is coated internally with a phosphor that converts this UV radiation into light. Thegeneral construction of the lamp is shown in Fgure 3.19 below.

Figure 3.19 Construction of a high pressure mercury lamp

Support for discharge tube

Discharge tube

Outer bulb

Main electrode

Auxiliary electrode

Resistor

Lamp cap


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The operation of the lamp is quite complex and needs to be considered in three phases:ignition, run-up and stable running.

First ignition; when power is first applied to the lamp the voltage is not high enough to strike anarc between the two main electrodes. Ignition is achieved using an auxiliary electrode placedclose to one of the main electrodes. The auxiliary electrode is connected via a resistor (typically25,000 ohms). This limits the size of the current in the arc formed by the auxiliary electrode sothe voltage across the starting arc is reduced as the current increases. This means that the ionsin the arc are drawn towards the main electrode at the other end of the lamp and these ionsallow the main arc to start.

The next stage is the run-up. Once the arc has started between the main electrodes very littlelight is given out because the mercury pressure is too low as the tube is cool. The arc in the gasslowly warms up the tube and so the mercury vapour pressure rises and the light outputincreases. Typically it takes about 4 minutes for the lamp to achieve 80% of the final lightoutput.

When the lamp reaches stable running and normal operating pressure all the mercury in the lampis in the vapour phase. This means that the vapour pressure of the mercury is controlled by theamount of mercury put into the lamp rather than the temperature of the lamp.

High pressure mercury lamps are made from the following main components.

The discharge tube is generally made of quartz and has the main electrodes and the startingelectrode sealed into it.

The main electrodes are usually made of tungsten rods which have coil of tungsten wire wrapped round them. This coil is usually impregnated with emitter material similar to that used in fluorescent lamps. The auxiliary electrode is generally wire made out ofmolybdenum or tungsten.

The fill gas in the discharge tube is commonly argon and a very carefully controlled dose ofmercury is also added. The discharge tube is fitted into a support frame and the whole assemblyis sealed into the outer bulb. The gas fill in the outer bulb is usually nitrogen or argon or amixture of the two. The pressure of this fill gas is controlled to ensure that the arc tubeoperating temperature is correct.

The outer bulb is made out of a soft soda lime glass for low wattage lamps (up to 125 W). Highpower lamps use a borosilicate glass outer. There are two common shapes for the outer bulbthe ovoid or isothermal bulb, and the reflector bulb. Figure 3.20 show these two shapes.


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Figure 3.20 Forms of high pressure mercury lamps

The performance of these lamps is not considered to be very good nowadays. Their efficiency isaround 40 lumens per watt. Their CIE general colour rendering index is between 40 and 50 and they have a very long life but, because of poor lumen maintenance, it is generallyrecommended that the lamps are changed after 8,000 to 10,000 hours of use.

Because of their poor performance and the fact that better lamp types are available for almost allof the applications these lamps are being phased out.

3.3.5 Metal halideMetal halide lamps were developed as a way of improving the performance of high pressuremercury lamps in terms of their colour appearance and light output. They work by introducingthe salts of other metals into the arc tube. As each element has its own characteristic spectralline, by adding a mixture of different elements into the discharge it is possible to create a lightsource with good colour rendering in a variety of colours.

There are a lot of problems with introducing new elements into a discharge. First, the elementmust be volatile and secondly it should not chemically attack the arc tube. To avoid theseproblems it has become common practice to introduce metals into the lamp as metal halides.Metal halides are generally more volatile than the metals themselves and the metal halides donot attack the arc tube. The metal halide compound breaks up into the metal and halogen ionsat the high temperatures in the centre of the discharge and reforms at the lower temperaturesnear the wall of the tube.

Many different combinations of elements have been used to make metal halide lamps, Figure3.21 lists some of the more common combinations of elements together with the spectraloutput they create.


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Dysprosium lamp with thulium, holmiumand thallium additives.

Three colour (indium, thallium, sodium)metal halide lamp. The lithium line is dueto impurities in quartz of the tube wall.

Scandium lamp with sodium additive. Thulium lamp with a range of additives.

Tin halide lamp with sodium additive.

Figure 3.21 Relative spectral power distributions of metal halide lamps

300

Rel

ativ

esp

ectr

alp

ow

er

400 500 600

Wavelength (nm)

ln, Ti, NaT = 4500 K

Ra = 61

700 300

Rel

ativ

esp

ectr

alp

ow

er

400 500 600

Wavelength (nm)

Dy, (Tm, Ho, Tl)T = 5600 K

Ra = 86

700

300

Rel

ativ

esp

ectr

alp

ow

er

400 500 600

Wavelength (nm)

Sc, NaT = 3800 K

Ra = 56

700 300

Rel

ativ

esp

ectr

alp

ow

er

400 500 600

Wavelength (nm)

Tm, (Dy, Ho, Tl, Na)T = 4300 K

Ra = 87

700

300

Rel

ativ

esp

ectr

alp

ow

er

400 500 600

Wavelength (nm)

SnI2/SnCl2(Na)T = 3000 K

Ra = 74

700

ln

ln

Tl Na

LiDy

Tl

Sc HgSc

Sc Sc

Na

Sc Li

Hg

Na

Li

Tl

Dy

Na

LiHg


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Because of the differing lamp chemistry there is a wide range of lamps that vary in terms oftheir efficacy, colour and electrical properties.

One of the main problems with metal halide lamps that use quartz discharge tubes is colourstability. As the colour of the light output is a function of the ions present in the discharge tube,any changes to the gas composition due to some metals being absorbed by the quartz tube orchanges in temperature in the tube can cause significant colour shifts. These colour shifts areparticularly a problem for the lower wattage lamps. This problem has largely been solved by theintroduction of a new material for the discharge tube. Ceramic or sintered alumina tubes aremuch more resistant to chemical attack than quartz tubes and can operate at highertemperatures. Lamps with these tubes are now very popular for low wattage (up to 150 W)metal halide lamps.

The construction of a metal halide lamp is similar to that of a high pressure mercury lamp.The key differences are that it is unusual to use an auxiliary electrode in the lamp, lamp ignitionbeing achieved using a high voltage pulse from the control gear. Also, there is no phosphorcoating on the outer bulb.

There are a wide variety of shapes of lamp. Figure 3.22 shows some of them.

Figure 3.22 Forms of metal halide lamps


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There is a vast range of metal halide lamps ranging in power between 20 W to over 2 kW. Thelamps have a CIE general colour rendering index between 60 and 93 and they have highluminous efficacies, in the range 60 to 98 lumens per watt. For these reasons, this lamp type hasmany applications where a compact light source with good colour rendering is needed.

There are many points to watch for when selecting metal halide lamps as there are problemsassociated with some lamp types shattering at the end of life or giving off UV radiation. It isimportant with these lamps to ensure that the luminaire in which they are used is suitable.

3.3.6 Low pressure sodiumLow pressure sodium lamps are similar in many ways to fluorescent lamps as they are both lowpressure discharge lamps. All the differences in characteristics stem from the use of sodium inthe discharge tube rather than mercury. The key differences are the need to run the lamp hotterto maintain the vapour pressure of sodium, the need to contain the very reactive sodium metal;and the fact that sodium emits its light in the visible rather than the UV frequency range, sothere is no need for a phosphor layer.

There used to be a range of designs for sodium lamps but currently the U-tube lamp is by farthe most common type. A typical lamp of this design is shown in Figure 3.23.

Figure 3.23 The constructionof a low pressuresodium lamp

Bend Isolation

Discharge tube

Dimple filled with sodium

Outer bulb

Electrode

Getter

Lamp cap


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The main components of a low pressure sodium lamp are as follows.

The arc tube; this is made of normal soda lime glass with a coating on the inside of a specialsodium resistant aluminoborate glass. Making this ‘ply-glass’ tube is technically difficult as greatcare is needed to ensure that there are no thermal stresses in the final tube that might lead tocracking during the life of the lamp. Some lamp types have dimples in the side of them to act asreservoirs of sodium.

The gas fill of the tube is neon with about 1% of argon at a pressure of approximately 1000 Pa.This mixture is used as it has a much lower breakdown voltage than neon on its own and thusmakes starting the lamp much easier. Sodium metal is also put into the tube. The sodiumvapour pressure in the tube when it is at its operating temperature of 260 ˚C is about 0.7 Pa.

The outer bulb is of soda lime glass, the inside is coated with a layer of indium oxide. This layerreflects the bulk of the infrared radiation from the arc tube and thus keeps it warm. Betweenthe outer bulb and the arc tube the gas pressure is very low, below 0.01 Pa. To maintain thevacuum a barium getter is used.

A relatively high voltage is needed to start an arc in the neon fill gas. The arc then slowly warmsup the lamp and the discharge tube and the vapour pressure of the sodium starts to rise untilthe lamp reaches thermal stability after about 15 minutes.

One of the curious properties of the sodium atom is the predominance of the energy transitionsassociated with the two spectral lines at 589 nm and 589.6 nm. This means that virtually all thevisible radiation from the lamp is given off in this very narrow band. However, sodium atomswill also re-absorb and re-emit the radiation very readily; this means that nearly all the lightemerging from a low pressure sodium lamp has come from close to the arc tube wall.

The light from a low pressure sodium lamp is a wavelength close to the peak of the photopicsensitivity curve, and as the lamp is relatively efficient at converting electricity into visibleradiation, the lamp is one of the most efficient light sources in terms of lumens per watt. Thebest of the range can achieve in excess of 180 lumens per watt. The problems with the lamp arelarge size, long run-up time and monochromatic light that does not render colours. The lamphas been mainly used for street lighting but recently the importance of some colour renderingon roads has been recognised and the lamp is rarely used in new installations.

3.3.7 High pressure sodiumThe high pressure sodium lamp generates light in a discharge through sodium vapour at highpressure. As the vapour pressure of sodium in a lamp rises the spectrum at first broadens andthen it splits in two with a gap appearing at about 586 nm. Figure 3.24 shows the spectra fromsodium lamps with different vapour pressures.


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Low pressure sodium lamp; sodiumvapour pressure 0.7 Pa

As the vapour pressure rises the colour rendering of the lamp increases. However, this is at theexpense of efficacy in terms of lumens per watt. Figure 3.25 shows the construction of a highpressure sodium lamp.

Figure 3.25The construction of a high pressuresodium lamp

Standard high pressure sodium lamp;sodium vapour pressure 10 kPa

Colour improved high pressure sodiumlamp; sodium vapour pressure 40 kPa

White high pressure sodium lamp;sodium vapour pressure 95 kPa

400

Rel

ativ

esp

ectr

alp

ow

er

500 600 700

Wavelength (nm)

T = 1700 K

400

Rel

ativ

esp

ectr

alp

ow

er

500 600 700

Wavelength (nm)

T = 2000 KRa = 23

400

Rel

ativ

esp

ectr

alp

ow

er

500 600 700

Wavelength (nm)

T = 2150 KRa = 40

400

Rel

ativ

esp

ectr

alp

ow

er

500 600 700

Wavelength (nm)

T = 2500 KRa = 80

Top support

Discharge tube ofsintered alumina

Hellical support wire

Outer bulb

Electrode

Flexible connection to allowfor thermal expansion

Getter

Figure 3.24 The spectra of sodium lamps with different vapour pressures of sodium


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The main components used in the construction of the lamp are as follows.

The arc tube is made of polycrystalline alumina (PCA). This material is ceramic rather than aglass, this makes it very hard to work as it is not possible to soften it and it is hard to cut. PCAis used because it is resistant to chemical attack by hot sodium, it is stable at high temperaturesand it is transparent.

Because it is not possible to work the PCA the tube is cut to length and fitted with end caps,Figure 3.26 shows some of the designs used for closing the ends of the discharge tube.

Figure 3.26 Types of arc tube seal in high pressure sodium lamps

The use of niobium metal as part of the end cap assembly is common as it expands withtemperature at the same rate as the PCA tube and thus does not cause stresses in the lamp as it heats up.

The electrodes in the lamp are made from tungsten rods with tungsten wire wound around them,with emitter material made from oxides of metals such as barium, calcium and yttrium.

Monolithicarc tube

Aluminadisc

Niobiumsupport wire

Niobiumtube

Sealglass

Aluminadisc

Sealglass

Seal glass Niobiumwire

Aluminabushing

Niobiumexhaust tube

a

Metallicbraze

Titaniumbraze

Niobiumtube

Niobiumcap

b

c d


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The fill gas in the tube is usually xenon at a cold pressure of 3 kPa, which corresponds to anoperating pressure of about 20 kPa. A higher xenon pressure would improve lamp efficacy butmake starting harder as it needs a high voltage to break down. Some types of lamp use highpressure xenon and use an ignition wire held close to the tube to help starting. There are alsosome lamps that use argon as a fill gas; they are much easier to start but are less efficient in termof lumens per watt. A dose of sodium mercury amalgam is used in most high pressure sodiumlamps. Mercury is used because its vapour acts as a buffer gas and helps improve the efficiencyof the lamp. However, the mercury contributes very little to the output spectrum of the lamp.Some lamps are now made without mercury in them. The absence of mercury makes thedisposal of the lamp at the end of life easier as there are no environmentally damagingsubstances in the lamp. The metal dose in the lamp is never fully vapourised and so thepressure of the sodium and mercury vapours in the lamp is dependent on the temperature ofthe coolest part of the discharge tube. This makes the output of the lamp temperaturedependent and can also give problems associated with the voltage across the tube rising if thelamp gets too hot. The cold spot on most discharge tubes is in the area behind the electrode.As this area of the tube is blackened through the life of the lamp, the cold spot temperaturetends to rise through life. This can give rise to problems in old lamps where the pressure in thedischarge tube rises to the point where it is no longer possible for the voltage available from thesupply to sustain an arc in the lamp.

The discharge tube is mounted into a support frame and sealed into an outer bulb. The outer bulbis generally made of a borosilicate glass and may be in a number of different shapes, Figure 3.27shows some of the more common shapes.

Tubular outer bulb

Figure 3.27 Outer bulb shapes for high pressure sodium lamps

Linear double ended ina quartz outer bulb

Ellipsoidal or isothermalcoated outer bulb

Reflector bulb


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The high pressure sodium lamp is an efficient source of light (efficacies up to 142 lumens perwatt), it has a long life with reasonable lumen maintenance and whilst the colour rendering onthe standard lamp is poor it is acceptable for a number of applications.

The white high pressure sodium lamp has a spectrum with minimal output in the yellow. Thishas the property of making a large number of colours appear more vivid and so this lamp has anumber of applications in retail lighting.

3.3.8 InductionInduction lamps are essentially gas discharge lamps that do not have electrodes. Instead theelectric field in the lamp is induced by an induction coil that is operating at high frequency.The only types of induction lamps that are currently in production are based on fluorescentlamp technology. Figure 3.28 shows the layout of a cavity type lamp.

The lamp consists of a glass bottle with a cavity in it into which the induction coil is placed.The glass vessel has a gas filling similar to a conventional fluorescent lamp and the phosphorcoating on the inside of the lamp is also similar.

The induction coil in the centre of the lamp is fed from a high frequency generator.

An alternative architecture for this type of lamp is to have the induction coil wrapped around atoroidal lamp. Figure 3.29 shows a lamp of this type.

Figure 3.28Construction of a cavity type induction lamp

Figure 3.29 An external coilinduction lamp

Phosphor coating

Plastic housing

Electron/ion plasma

Induction coil

Electronics


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Induction lamps have many of the same properties as fluorescent lamps. They are, however,slightly less efficient. The big advantage with this type of lamp is long life. This is because there are no electrodes to fail and the inside of lamp does not get coated with material that hasbeen vapourised away from the electrodes. A number of lamps of this type have rated lives of100,000 hours. These lamps are more expensive than conventional fluorescent lamps so they tend to be used in places where it is difficult to change lamps and thus long life is animportant requirement.

3.3.9 Light emitting diodesThe basic operating principle behind light emitting diodes (LEDs) is covered in section 3.1.3.LEDs are available in a wide variety of sizes, colours and power ratings and development isproceeding at a rapid rate (see the Lighting Industry Federation LED Guide 2005 and the EBVElectronik and Philipslumileds web sites). Whilst LEDs come in a variety of styles, Figure 3.30illustrates two common forms.

The main components of a LED are as follows.

The chip of semiconductor material in the centre of the lamp may be made of a wide variety ofmaterials. Differing materials result in a different colour of light being produced Table 3.4 listssome of the more commonly used materials.

The chip is mounted onto one of the lead in wires. In high power LEDs the mounting isdesigned in such a way as to conduct heat away from the chip. The other lead wire is bonded tothe chip generally connecting to a very small area close to the actual semi conductor junction.The whole device is then potted in a plastic resin, usually epoxy.

Materials

Aluminum gallium arsenide (AlGaAs)

Aluminum gallium phosphide (AlGaP)

Aluminum gallium indium phosphide (AlGaInP)

Gallium arsenide phosphide (GaAsP)

Gallium phosphide (GaP)

Gallium nitride (GaN)

Indium gallium nitride (InGaN)

Zinc selenide (ZnSe)

Aluminum nitride (AlN), Aluminum gallium nitride (AlGaN)

Diamond (C)

Radiation

Red and infrared

Green

Orange-red, orange, yellow, and green

Red, orange-red, orange, and yellow

Red, yellow and green

Green, pure green (or emerald green),and blue

Near ultraviolet, green, bluish-greenand blue

Blue

Near to far ultraviolet

Ultraviolet

Table 3.4 Materials used in LEDs and the radiation produced


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Figure 3.30 The construction of low power (left) and high power (right) LEDs

LEDs generally have a long life and may last up to 100,000 hours. LEDs generally emit light ina relatively narrow band so that most LEDs produce light that is a saturated colour. It is possibleto make white LEDs by using a blue or ultraviolet chip and putting a phosphor coat round it.White can also be achieved by combining a mixture of red, green and blue chips.

LEDs have a lot of applications associated with signals and signage. The use of saturated coloursin these applications is a real bonus. This coupled with the ease of producing light in a numberof small units means that LEDs are replacing a number of other light sources in these areas. It is also possible to make lamps that are a cluster of LEDs of different colours. By controllingthe outputs of the different colours it is possible to make a lamp that can produce light in awide variety of colours. At the time of writing, white LEDs are making fast technical progressbut have not proved to have that many applications in the area of general lighting as the lumenpackages tend to be small and their efficacy does not compare favourably with other sourcessuch as fluorescent lamps.

3.3.10 ElectroluminescentThe basic principles of electroluminescent (EL) light sources are discussed in section 3.1.3.Generally the light sources are made up as panels with a construction similar to that shown in Figure 3.31.

Figure 3.31 A section through an electroluminescent panel

Transparent medium

Conducting layer

Phosphor plus phosphor embedding layer

Conductive material

S

LED Chip

Reflector

Cathodelead

Light emitted forward

Epoxyhousing

PC board

Anodelead

Plastic lens

Siliconencapsulation

InGanLED chip

Solderconnection

ReflectorcupHeat slug

Cathodelead Gold

wire

Light emitted forward


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The EL panel is made up of the following components.

The lower conductor carries one side of the electrical supply into the light source. In older typesof panel this conductor may have been a sheet of metal, but in the newer flexible panels it isgenerally some type of foil.

The phosphor layer contains the phosphor used to generate the light together with a medium,usually some form of plastic resin, used to keep the grains of phosphor apart from one another.

The top conductor is a made of a transparent material that conducts electricity to the top surfaceof the phosphor layer.

The top layer of the device is a transparent medium. In older devices this layer is usually madeof glass, but in more modern units it is likely to be a flexible transparent film.

EL panels are not a particularly efficient light source. Typically they have efficacies of a few lumens per watt. The light output of an EL panel is not that great, typically less than 300 lumens per square metre. There are many applications for EL panels as it is relatively easy to cut them to shape and size so they can be used for signage and to backlight displays inelectronic equipment.

3.4 Electric light source characteristics

There are a number of key properties of lamps that need to be considered when choosingwhich lamp is right for a particular application. The following sections list these properties.

3.4.1 Luminous fluxIn any lighting application the amount of light that is needed is a key decision that has to bemade. From this it is then possible to work out how many lamps of given rating are needed.There are lamps with lumen outputs less than 1 lumen through to lamps with outputs in excessof 200,000 lumens. In most applications, it is the average maintained illuminance that isimportant so it is important to consider the lumen maintenance through life at the same time as the initial luminous flux.

3.4.2 Power demandIt is important in any lighting scheme to know what the total power demand is going to be sothat the electrical infrastructure can be correctly designed. The power consumed by the lamp isimportant. However with many lamp types it is important also to consider the impact of thecontrol gear as well. In most cases it will be the total circuit watts that is important rather thanthe lamp wattage.

One further complication with some lamp types is that the voltage and current waveforms arenot exactly in phase with one another. Thus the volts multiplied by the amps in the circuit maybe higher than the watts. The power factor of the circuit is defined by the following equation:

power factor =watts

volts × amps


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Most high wattage lamp circuits are designed to have a power factor greater than 0.85. The other factor that may affect the sizing of the cables that supply a lighting installation is thecurrent required during the run-up of the lamps. With some types of lamp this can be overdouble the nominal running current. When using lighting controls the power demand is moredifficult to predict as the power consumed may be reduced at times when full output is notrequired from the lamp.

3.4.3 Luminous efficacyLuminous efficacy is usually expressed in terms of lumens per watt. Many lamp manufacturersproduce lumens per watt figures for their lamps. However, for discharge lamps and other lampsrequiring some form of control gear, these figures may be misleading as they refer to the powerconsumed in the lamp only and do not consider the power lost in the control gear. All thevalues quoted in this chapter for efficacy are based on total circuit watts.

Efficacy is a primary concern when selecting a lamp. In general, if a range of lamps suitable fora particular installation then it is the most efficient that should be used.

3.4.4 Lumen maintenanceThe light output of most lamps decreases as the lamps get older. With some relatively short life lamps this is not a problem as they fail before the light output has fallen significantly. See Section 21.7.1 for further details of the lamp lumen maintenance factor (LLMF).

3.4.5 LifeIt is normal when considering the life of a lamp to talk about the percentage of lamps that willsurvive after a certain number of hours of operation. This value is known as the lamp survivalfactor (LSF). See Section 21.7.2 for further details.

Other factors in a particular installation may affect the life of the lamp used. These factorsinclude the switching frequency, the supply voltage, the ambient temperature and presence of vibration.

It is often the case that the combined effect of the number of lamp failures coupled with thereduced lumen output of the lamps makes it necessary to replace the lamps in an installation.Sometimes lamp makers quote an economic service life for lamps, this generally is the point where the LSF multiplied by the LLMF falls below 0.7.

3.4.6 Colour propertiesThe colour of the light produced by a lamp is generally described by two parameters; thecorrelated colour temperature and the CIE general colour rendering index. These two terms are described in Sections 1.4.3 and 1.4.4 respectively

For most applications there is a minimum requirement for the colour rendering properties ofthe lamps used and the correlated colour temperature of the source is generally chosen for theatmosphere that the lighting is designed to produce.

3.4.7 Run-up timeWhen a lamp is switched on it takes a certain amount of time to reach full light output. The usual measure used to assess run-up time is the time that it takes for a lamp to reach 80% of its full output.


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For a GLS lamp this might be a fraction of a second, while for low pressure sodium this couldbe as much as 20 minutes. For some applications such as road lighting the run-up time is notimportant. However, for occasionally used rooms in a home it is very important.

3.4.8 Restrike timeWhen some gas discharge lamps go out due to an interruption in the mains supply it is notpossible to restart them until the lamp has cooled down. This may take several minutes. Theuse of lamps with a long restrike time may cause problems in some installations due to thepossibility of a small power outage causing a long blackout.

3.4.9 Other factorsThere are also many other factors that impact upon the use of lamps in a particular application.These factors include the following.

Lamp size: some lamps are too large for certain applications, whilst some small lamps mayproduce too high a luminance for others.

Burning position: not all lamps may be used in all orientations, for some discharge lamps, lampmanufacturers produce diagrams similar to Figure 3.32 to show which burning positions arepermitted. The figure shows that the lamp in question must only be used in the horizontalposition ± 20˚.

Figure 3.32 A typical restricted burning position symbol

Dimming: it is not possible to dim all lamp types and some types may be only dimmed down togiven percentage of their output. Dimming for some lamps may require the use of specialcontrol gear.

Ambient temperature: not all lamps will run at a given temperature. For example some compactfluorescent lamps are not suitable for outdoor use as they will not start if they are too cold.

Disposal of lamps: lamps may contain hazardous substances such as lead, sodium and mercury.This may mean with particular lamps particular procedures have to be followed when disposingof the lamps. Under the WEEE Directive of the European Commission it is the responsibilityof the lamp manufacturer to provide the means of recycling used lamps. Seehttp://www.recolite.co.uk for more information about the recycling of lamps in the UK

3.4.10 Summary of lamp characteristicsTable 3.5 gives a summary of the key characteristics of the main lamp families.


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Tab

le3.

5Su

mm

ary

ofla

mp

char

acte

rist

ics

Lam

pna

me

GLS

TH

T12

(4)

T8

T5

Com

pact

(CFL

)

CFL

ni(N

onin

tegr

alco

ntro

lgea

r)

CFL

i(In

tegr

alco

ntro

lgea

r)

MB

F/H

PL

Qua

rtz

tube

Cer

amic

Tube

Out

put

rang

e(l

m)

5–12

,000

40–5

0,00

0

1000

–10,

500

650–

6200

120–

8850

250–

9000

100–

1500

2000

–58,

500

5,20

0–20

0,00

0

1,60

0–26

,000

Pow

erra

nge

(W)

1–10

00

4–20

00

25–1

40

13–7

0

6–12

0

8–12

0

5–30

60–1

040

85–2

050

20–2

50

Eff

icac

y(l

m/W

)

8–14

15–2

5

50–8

0

50–9

6

20–9

3(6

)

30–7

0

20–5

0

33–5

7

60–9

8

65–9

7

Col

our

tem

p(K

)

2500

–270

0

2700

–320

0

3000

–650

0

2700

–170

00

2700

–170

00

2700

–650

0

2700

3200

–390

0

3000

–600

0

3000

–440

0

Col

our

rend

erin

g(R

a)

100

100

(3)

50–

90

50–9

8

82–9

5

85–9

0

>80

40–5

0

60–9

0

78–9

3

Run

-up

time

Inst

ant

Inst

ant

30se

c

30se

c

30se

c

15–9

0se

c

60se

c

4m

in

1–8

min

2m

in

Dim

min

g

Eas

yto

0%

Eas

yto

0%

Lim

ited

to25

%

Eas

yto

2%

Eas

yto

2%

Som

ety

pes

to5%

Som

ety

pes

to20

%

No

No

Lim

ited

(7)

Life

(h)

(1)

1,00

0

1,50

0–5,

000

8,00

0–12

,000

8,00

0–17

,000

(5)

8,00

0–19

,000

(5)

Up

to15

,000

(5)

5,00

0–15

,000

8,00

0–10

,000

2,00

0–

7000

6,00

0–10

,000

Com

men

ts

Larg

eva

riet

yof

shap

esan

dsi

zes

ofla

mp

The

rear

eso

me

high

erpo

wer

lam

psav

aila

ble

for

spec

ial

appl

icat

ions

such

asco

ldst

ores

The

lam

pra

nge

isin

crea

sing

rapi

dly

Con

trol

gear

No

No

(2)

Yes

Yes

Yes

Yes

No

Yes

Yes

Yes

Inca

nde

scen

t

Fluo

resc

ent

Hig

hpr

essu

rem

ercu

ry

Met

alh

alid

ela

mps


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Life

(h)

(1)

15,0

00–2

0,00

0

10,0

00–2

0,00

0

10,0

00–1

4,00

0

6,00

0–9,

000

60,0

00+

15,0

00–6

0,00

0(9)

1E

cono

mic

lam

plif

em

aybe

limite

dby

lum

ende

prec

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n.2

Alo

tofT

Hty

pesa

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signe

dto

run

onlo

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ltage

sand

thus

need

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tosu

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nece

ssary

volta

ge.

3So

me

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rsha

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red

end

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usdo

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of10

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form

atio

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mla

mp

mak

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isto

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dto

find.

4T

12la

mps

are

notg

ener

ally

used

inne

win

stalla

tions

asT

5an

dT

8ty

pesa

rem

ore

effici

ent.

5L

amps

also

avai

labl

ew

ithex

ceed

ingl

ylo

ngla

mp

lives

ofe.g

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000

hour

sand

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00ho

urs.

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ostT

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are

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ture

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The

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can

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and

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tially

50%

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,whe

nbu

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toa

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utan

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rem

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steep

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istin

got

herl

amp

techn

olog

ies.

9Fo

rlam

plif

ebo

thele

ctrica

lfai

lure

sand

lum

enm

aint

enan

cesh

ould

beco

nsid

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tom

easu

rem

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tand

ards

e.g.B

10/L

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lfai

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Lam

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SOX

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Std

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Del

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N

Whi

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Out

put

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1,80

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,000

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0,00

0

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7,00

0

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0–5,

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2,60

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20

Pow

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85–1

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45–1

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55–1

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Eff

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0

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Col

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65 83 80

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5

Run

-up

time

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0m

in

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min

5m

in

2m

in

1m

in

Inst

ant

Dim

min

g

No

Lim

ited

to25

%

Lim

ited

to25

%

No

No

Eas

yto

0%

Com

men

ts

Goo

dlu

men

mai

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ance

,bu

tpow

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ptio

ngo

esup

thro

ugh

life

The

rang

eof

LED

sis

incr

easi

ngra

pidl

y

Con

trol

gear

Yes

Yes

Yes

Yes

Yes

Yes

Low

pres

sure

sodi

um

Hig

hpr

essu

reso

dium

Indu

ctio

n

Col

our

tem

p(K

)

N/A

1,90

0–2,

100

2,15

0

2,50

0

2,55

0–4,

000

2,68

5–65

00

LE

Ds(

8)

Tab

le3.

5Su

mm

ary

ofla

mp

char

acte

rist

ics

cont

...


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3.5 Flames

Historically flames were the first form of artificial lighting. They are occasionally still used tocreate a particular atmosphere, but they are not considered as major sources of artificial light.

3.5.1 CandleIt is said that the ancient Egyptians invented the candle. They made candles by soaking reeds inmolten tallow (animal fat). However this was not the candle as we know it today as it had nowick as such. It appears that the Romans made the first true candle with a wick, but it still used tallow.

The problem with tallow candles is that they produce a lot of smoke and acrid smells. In theMiddle Ages beeswax was introduced for making candles. It overcame the problems of tallowcandles, but due to its cost only rich people could afford them. The last advance in candlemaking was in the 19th century when whale oil wax and paraffin wax were introduced.

The actual processes involved in a candle burning are very complex; in 1861 Michael Faraday was able to fill a series of six lectures just discussing them. The key points of the process arethat the heat of the candle flame melts the wax, which is absorbed in the wick, which transportsit to the flame where it is burnt. In the burning process some particles of carbon are produced. These particles glow as they are hot.

3.5.2 OilThe oil lamp has been around for a very long time. Some of the earliest examples are hollowedout stones that were filled with oil and these may be 70,000 years old. There are examples ofearthenware lamps made by all the ancient civilisations. In Europe the most common oils used in these lamps were olive and colza. The wick was generally made out of bark, moss orplant fibres.

The first major development in modern history was the use of a flat wick in the lamp that started in 1773 and the tubular wick in 1784. This coupled with the glass chimney made thelamps significantly more efficient. Figure 3.32 shows such a lamp.

Figure 3.32An oil lamp with a tubular wick and a glass chimney


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In the 1860s with the introduction of paraffin the oil lamp became very popular and was one ofthe leading sources of artificial light until it was overtaken by gas and electric lighting.

3.5.3 GasGas lighting only became possible during the industrial revolution. During the 1780s severalinventors had been working with the flammable gas that is produced when coal is made intocoke and they realised that it could be used for lighting. The problem was that it becamenecessary to set up a whole infrastructure of pipes to supply the gas to where it was needed. In 1813 a company was set up in London to supply gas and by 1815 there were 26 miles of gas pipe installed.

The first gas light burners were little more than small openings at the end of a gas pipe. Over aperiod of time the shape of the burners evolved so that each unit would produce more light.However, a major improvement in performance was achieved in 1887 with the invention of thegas mantle. The gas mantle is a cube of fabric, impregnated with thorium and cerium oxides.When the lamp is lit the fabric burns away leaving a brittle mesh of oxides. The cerium oxide isa thermo-luminescent material, see Section 3.1.8.


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Chapter 4: Luminaires

4.1 Basic requirements

A luminaire is the apparatus containing the light source. A luminaire is designed to:

connect the light source to the electricity supply

protect the light source from mechanical damage

control the distribution of light

be efficient

withstand the expected conditions of use

be safe when used in the recommended manner.

To meet these design objectives it is necessary to consider the electrical, mechanical, optical,thermal and acoustic aspects of luminaires.

4.1.1 ElectricalElectrical wiringThe internal wiring of a luminaire has to be capable of handling the electrical current and thethermal conditions in the luminaire. The cross sectional area of the wire will determine themaximum allowable current. IEC 598 specifies a minimum cross section of 0.5 mm2 althoughthis may be reduced to 0.4 mm2 where space is severely restricted.

The wire itself can be solid or stranded. Solid wire is easier to hold in position and to strip,making it simpler to install in a luminaire. However, solid wire is not suitable for luminaires thatare subject to vibration or for luminaires that may be frequently adjusted. For such luminaires,stranded wire is better.

Both types of wire are covered with insulating material. The choice of insulation material islargely determined by its heat resistance. The wiring of a luminaire has to be capable ofwithstanding not only the air temperatures inside the luminaire but also the surface temperaturesof components that the wiring may contact, such as lamps, control gear and lamp holders. PVCinsulation that is heat resistant up to 90 ˚C, 105 ˚C and 115 ˚C is available. Where highertemperatures may be experienced, silicon rubber (170 to 200 ˚C) and PTFE (250 ˚C) insulationmay be used. Additional thermal insulation can be achieved by covering the electrical insulationwith a glass fibre sleeve.

Connection to the electricity supply There are three approaches commonly used to connect a luminaire to the electricity supply; theconnection block, automatic connection and through wiring.

The most common method is via a connection block within the luminaire. To prevent theconnection being accidentally broken, the supply wire should pass through a cable clamp beforereaching the connection block.

Luminaires mounted on trunking systems are often designed so that connection to the electricitysupply occurs when the luminaire is mounted on the trunking. For this to occur the electricalsocket carrying the electricity supply is part of the trunking and the plug is contained within the luminaire.

Final Lighting book artwork 08 sec2 25/3/09 10:08 Page 2

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sThe earth pin of the plug is longer than the live and neutral pins so that when the luminaire isoffered up to the track, the earth connection is made before the live and neutral, and whenremoving the luminaire, the live and neutral connections are broken before the earth.

Through wiring is a system for connecting a series of luminaires in parallel across a supplycable. This reduces the amount of cabling required and speeds up installation. The supply cableshould have a cross section of 2.5 mm2 as a minimum, but the wiring from the connectionblock in each luminaire may have a smaller cross section, typically 0.5 or 0.75 mm2.

EarthingMetal parts of Class 1 luminaires (see Section 4.3.2, Table 4.11) that are accessible when theluminaire is installed or open for maintenance or that may become live if the insulation failsshould be permanently connected to an earth terminal. The wire used for earthing should beat least 2.5 mm2 in cross section.

4.1.2 MechanicalThe mechanical integrity of a luminaire depends on the materials used and the quality of its construction.

MaterialsSteelMany interior lighting luminaires are made from ready-painted sheet steel, white being theusual paint colour. Where corrosion is a problem, galvanised sheet steel is used. Where a verydurable paint finish is required, enamelling is used.

Stainless steelStainless steel is rarely used for luminaire bodies but it is widely used for many small,unpainted luminaire components that have to remain free from corrosion.

Aluminium sheet Aluminium sheet is mainly used for reflectors in luminaires. It can have good reflectionproperties and the physical strength to form stable reflectors of the desired form.

Cast aluminiumCast aluminium is widely used for floodlight housings. Such housings are light in weight andcan be used in damp or corrosive atmospheres without any further treatment provided that thecorrect grade of aluminium has been used.

PlasticsThere are many different forms of plastic used in luminaires, either for complete housings orcomponents. These plastics differ in their transparency, strength, toughness, sensitivity to UVradiation and heat resistance.

GlassThree types of glass are used in luminaires; soda lime glass, borosilicate glass, and very highresistance glass. Soda lime glass is used where there are no special heat resistance demands.Where high heat resistance, chemical stability and resistance to heat shock are required,borosilicate glass is used. High resistance glass has the advantage that it can deliver high heatresistance, high thermal shock resistance and great physical strength even in thin sheets.


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CeramicsSome components of luminaires that produce very high temperatures are made of ceramics.

ConstructionAll luminaires should be designed to withstand the rigours of transport to the site, installationand prolonged use. Generally, exterior luminaires need to be more substantial than thosedesigned for interior use. Some luminaires are designed to resist the ingress of foreign objects,dust and moisture. Such luminaires have a transparent front cover and all points of access to theluminaire have a seal. Front covers are usually made of glass or plastic. Where there is a risk ofphysical impact, as in a sports hall, glass or acrylic front covers need to be covered with a wirescreen. If a polycarbonate front cover is used, no such screen is necessary. As for the seals, thesecome in various forms from a simple felt seal to convoluted notched rubber seals. The effectiveness of these seals is quantified by the IP classification system (see Section 4.3.2 Table 4.10).

4.1.3 Optical controlOptical control of the light output from a light source is achieved by some combination ofreflectors, refractors, diffusers, baffles or filters.

ReflectorsThree types of reflector are used in luminaires; specular, spread and diffuse.

Specular reflectors are used when a precise light distribution is required. The shape of thereflector and its position relative to the light source determine the light distribution. The mostcommon shapes for reflectors are circular, parabolic and elliptical.

A circular reflector with a point light source at its focus will produce a light distribution of thetype shown in Figure 4.1, reflections from some parts of the reflector being almost parallelwhile those from parts of the reflector away from the axis are divergent. This type of circularreflector is used in cylindrical form for picture lighting using tubular incandescent andfluorescent light sources.

Figure 4.1 The light distribution from a circular reflector with a point light source at its focus


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Figure 4.2 The light distribution from a circular reflector with a point light source at itscentre of curvature

A parabolic reflector with a point light source at its focus produces a parallel beam of reflectedlight (Figure 4.3). Moving the light source in front or behind the point of focus will cause thebeam to converge or diverge. The parabolic reflector is widely used in spotlight design eitherexactly, when the reflector is smooth, or approximately, when the reflector is facetted.

Figure 4.3 The light distribution from a parabolic reflector with a point light source at itsfocus. The beam intensity will be greater at the centre than at the edge — compare cones aFband AFB.

A circular reflector with a point light source at its centre of curvature produces a lightdistribution of the type shown in Figure 4.2. This type of reflector is widely used in projectionsystems and spotlights to increase the amount of light delivered to the associated lens system.

a

b

A

B

F


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Figure 4.4 Elliptical reflectors showing the change in light distribution as the point lightsource is moved relative to the first focus (F)

Spread reflectors are deliberately distorted specular reflectors. They can be circular, parabolic orelliptical in cross section and spherical or cylindrical in form. The distortion takes the form ofmodulating the specular surface of the reflector by hammering (peening) to produce a regulararray of dimples, or by etching or brushing the surface. The advantage of this distortion is thatit smears out variations in light distribution caused by inaccuracies in the manufacture of thereflector and the size of the light source. Spread reflectors are used where a well-defined buteven light distribution is required.

Diffuse reflectors are the opposite of specular reflectors. Unlike a specular reflector, the shapeof a diffuse reflector has only a small effect on the light distribution. Diffuse reflectors areused where there is a need to redirect light with a very wide beam.

Many different materials are used in reflectors. Typical values of reflectance for these materialsare given in Table 4.1.

RefractorsRefractors control light distribution by turning the incident light ray through a desired anglefollowing Snell’s Law. This can be done using either prisms or lenses. For luminaires usinglarge area light sources, such as a fluorescent lamp, multiple prisms are moulded in atransparent material, usually acrylic or polycarbonate plastic. The number, location, angle ofincidence and shape of the different types of prism determine the light distribution. Forluminaires using a point light source a lens can be used. The position and shape of the lensdetermines the light distribution.

An elliptical reflector with a point light source at one focus will ensure that the reflected rays allpass through the second focus (Figure 4.4) Elliptical reflectors in trough form are widely usedfor tubular fluorescent luminaires.

FF


Reflectance

0.70

0.80

0.90

0.85–0.88

0.70–0.80

0.70–0.85

0.55–0.58

0.50–0.55

0.60–0.70

Up to 0.84

Up to 0.90

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Reflector type

Specular

Specular

Specular

Specular

Spread

Spread

Spread

Spread

Spread

Diffuse

Diffuse

Material

Commercial grade aluminium

Aluminium with super purity coating

Aluminium with silver coating

Glass or plastic with aluminium coating

Peened aluminium

Etched aluminium

Brushed aluminium

Satin chromium

Aluminium painted steel

White paint on steel

Glossy white plastic

Table 4.1 Typical reflectance values for materials used in reflectors

DiffusersDiffusers are transparent materials that scatter light in all directions. They provide no control of light distribution but do serve to reduce the brightness of the luminaire. Diffusers arecommonly made of materials that maximise light scatter and minimise absorption, such as opal glass or plastic.

BafflesBaffles can have three functions; to hide the light source from common viewing angles, toreduce the amount of spill light, and to control the light distribution.

The extent to which the light source is hidden from view is quantified by two angles, theshielding angle and its complementary, the cut-off angle. The shielding angle is the anglebetween the horizontal and the direction at which the light source ceases to be visible. Figure 4.5 shows the shielding angle for a simple fluorescent luminaire.

Figure 4.5 The shielding angle for a simple fluorescent luminaire

Luminaire using aninternal baffle toimprove screening

Shielding angle. Beyondthis angle the lamp isnot visible to the user


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90

A common example of a baffle being used to hide the light source is the diffusely reflectinglouvre. This louvre can take a wide variety of forms, lamellae, eggcrate, concentric rings andhoneycomb depending on the shape and size of the luminaire and is usually made of a whitediffusely reflecting material. If the purpose is primarily to reduce spill light, the material usedfor the louvre will be of low reflectance, i.e. black. In addition to louvres, spill light can becontrolled by the use of low reflectance baffles, called barn doors, mounted on the luminaire(Figure 4.6).

If the purpose is to hide the light source and also to control light distribution, the louvre ismade from a specularly reflecting material and shaped so as to direct light downwards andhence increase the shielding angle (Figure 4.7). As a general rule, the finer the louvre and hence the more the light source is hidden, the lower will be the light output ratio of theluminaire (see Section 4.1.4).

Figure 4.6 Barn door bafflesmounted on aspotlight

Shielding angle ca. 45˚

Figure 4.7 A section through and an example of a louvre designed to hide the light sourceand control the light distribution

FiltersFor display and decorative lighting it is sometimes required to change the colour of lightemitted by a luminaire. This can be done by the use of filters, either absorption or interference.


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Absorption filters are usually made of plastic or glass. They absorb the unwanted wavelengthsand thereby raise their temperature. Plastic absorption filters are likely to change theirproperties if they get too hot. The transmittance of absorption filters is limited. Typicaltransmittances for different colour filters are blue = 5 percent, red = 20 percent, green = 15percent, and yellow = 40 percent. Another type of filter is the interference filter. Interferencefilters are more expensive and more exact than absorption filters and do not absorb theunwanted wavelengths. Rather, they split the light into two beams, one transmitted and onereflected, of two different colours (hence the name dichroic filters).

4.1.4 EfficiencyThe efficiency of a luminaire is quantified by its light output ratio (LOR). This is the ratio ofthe total light output of a luminaire to the total light output of the light sources used in theluminaire when operating outside the luminaire. LOR is sometimes split into upward anddownward components. LOR measures the efficiency of the luminaire in the sense that itquantifies how much of the light emitted by the light source escapes from the luminaire. LORdoes not measure the efficiency of a lighting installation. However, LOR is an element indetermining a lighting installation’s compliance with Part L of the Building Regulations. Lightoutput ratio is defined as the ratio of luminous flux emitted by the luminaire divided by theflux emitted by the bare lamps in free air. This means that for temperature sensitive lamps theLOR is a function of the increase in temperature of a lamp within the luminaire as well as theoptical efficiency of the luminaire.

4.1.5 ThermalAll luminaires increase in temperature when in operation. The internal temperature of theluminaire can affect the efficiency of some light sources and the associated control gear. Thesechanges in efficiency contribute to the light output ratio of the luminaire. The external surfacetemperature of a luminaire may also pose a fire hazard if mounted on a flammable surface (seeSection 4.3.2). Of course, the external temperature of the luminaire will increase more when itis surrounded by thermal insulation so care should be taken when considering recessingluminaires into confined or insulated spaces.

Air handling luminaires are used to deliver conditioned air to the occupied space or to extractheat from the occupied space and the luminaire. There are three types of air handling systemusing luminaires; plenum exhaust, single ducted and double ducted.

In a plenum exhaust system conditioned air is supplied through air diffusers, while stale air isextracted through slots in the luminaires into the plenum that acts as a return duct (Figure4.8a). The plenum exhaust system is only used where the maximum number of air changes perhour is less than six. In a single ducted system, conditioned air is delivered along the plenumand then through air diffusers, and stale air is extracted through the luminaires into a duct(Figure 4.8b). The single ducted system is used for spaces with low ceiling heights. In a doubleducted system conditioned air is delivered through air diffusers supplied by a duct, and stale airis extracted through the luminaires and an attached duct (Figure 4.8c). These three systemsdiffer in cost and efficiency. The double ducted system is the most expensive and most efficient.


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Figure 4.8 Sections through and drawings of (a) the plenum exhaust, (b) the single ductedand (c) the double ducted air handling systems

(a)

(b)

(c)


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sThe design of air conditioning incorporating luminaires is complex and requires knowledge ofheat load, air change rates, pressure drop and supply air temperatures. Failure to consider thesefactors carefully could cause the luminaires to fail to fulfil their function.

4.1.6 AcousticsLuminaires may amplify the sound produced by components in the luminaire, e.g. the controlgear, or produced elsewhere but transmitted to the luminaire through the building structure.Either way, the result is noise. Some spaces, such as concert halls have strict criteria aboutbackground noise, usually expressed as a noise rating (NR). A noise rating consists of numberedcurve showing the maximum sound pressure level allowed in each frequency band (Figure 4.9).Table 4.2 gives recommended NR values for different applications. Where noise is likely to be aproblem, care should be taken to use well constructed luminaires and to mount them so they arefree from vibration. It is also desirable to use high frequency control gear but if this is notpossible, remote positioning of control gear may be necessary.

Figure 4.9 A set of noise rating curves, plotted as sound pressure level at different frequencies

62.5 125 250 500 1000 2000 4000

Application

Studios

Concert halls

Conference rooms

Lecture rooms

Auditoria

Hospitals

Private offices

Noise rating

10

20

25

25

25

30

30

Table 4.2 Recommended noise rating values for different applications

70

60

50

40

30

20

10

0

Sou

nd

pre

ssu

rele

vel

(dB

)

Frequency (Hz)

–10

NR

70

50

40

30

20

10

0

No

ise

rati

ng

(NR

)

60


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4.1.7 EnvironmentalLuminaires may contain a variety of materials and some of these could be hazardous to theenvironment when the luminaire is disposed of at the end of life. To stop environmentalpollution there are two sets of European regulations, WEEE and RoSH.

WEEE or more fully the Waste Electrical and Electronic Equipment Directive requires that allluminaires are recycled at the end of life and are not just thrown away. To ensure that thisoccurs, luminaire suppliers are required to make provision for the collection and recycling ofold luminaires; see http://www.lumicom.co.uk for more information.

RoHS, the Restriction of Hazardous Substances Directive, controls the use of certain materialsused in luminaires. These materials such as lead, mercury, cadmium and polybrominatedbiphenyls are all toxic and their use in luminaires is limited.

4.2 Luminaire types

The lighting industry produces many thousands of different luminaires. Given below are briefoutlines of the main types of luminaire used in interior and exterior lighting. Details of any specific luminaire are best obtained from the manufacturers.

4.2.1 Interior lightingDirect luminairesDirect luminaires are luminaires in which the light distribution is predominantly downward(see Table 4.7). Such luminaires are typically recessed into or surface mounted on the ceiling.They are widely used in offices where the ceiling height is restricted. The usual light source is afluorescent lamp, either linear or folded. Many different forms of optical control are available,from diffusers through prismatic refractors to parabolic reflectors and louvres. Consequently,direct luminaires are available with a wide range of luminous intensity distributions. Directluminaires are available for operation in dirty, corrosive or hazardous conditions. Directluminaires are available with dimming or switching facilities linked to manual, occupancysensor and photocell control. The most common problems with lighting installations usingdirect luminaires is the creation of a dark ceiling and poor illuminance uniformity in obstructedspaces. This problem can be overcome by choosing direct luminaires with a little upward lightoutput or by having high reflection factors in the space. Figure 4.10 shows a direct luminaire.

Figure 4.10 An example of a direct luminaire


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sIndirect luminairesIndirect luminaires are luminaires in which the light distribution is predominantly upward (seeTable 4.7). Such luminaires can be suspended below the ceiling, wall mounted or free standing.They require a clean, white ceiling for efficient operation. Indirect luminaires are most practicalwhere the ceiling height is over 2.75 m. The usual light source in suspended indirect luminairesis a linear fluorescent lamp. Wall mounted and free-standing indirect luminaires tend to use ahigh intensity discharge lamp. Optical control is confined to ensuring that the light output fromthe luminaire is widely spread across the ceiling so that no hot spots of high luminance areapparent. While indirect luminaires have a high light output ratio, lighting installations usingindirect luminaires are usually less energy efficient than those using direct luminaires becauseof the losses caused by having to use the ceiling as a secondary reflector. This is compensated bythe bright appearance of the space, the high level of illuminance uniformity and the absence ofdiscomfort glare. Figure 4.11 shows a selection of indirect luminaires.

Figure 4.11 Examples of indirect luminaires

Direct/indirect luminairesDirect/indirect luminaires are luminaires in which the light distribution is evenly dividedbetween the upward and downward directions. In many ways, direct/indirect luminairesprovide the best of both worlds. The energy efficiency of a lighting installation using direct/indirect luminaires will be higher than that of one using indirect luminaires but the problemsof dark ceilings and poor illuminance uniformity are reduced by the indirect component. Direct /indirect luminaires are suspended below the ceiling. They are difficult to use where theceiling height is below about 2.75 m. The usual light source in direct/indirect luminaires is alinear fluorescent lamp. Optical control is different for the two directions of light output, beingmuch tighter for the downward component than the upward. Direct/indirect luminaires areavailable with individual dimming of the direct component. Figure 4.12 shows a selection ofdirect/indirect luminaires.

Figure 4.12 Examples of direct/indirect luminaires


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DownlightsDownlights are a form of direct luminaire characterised by a small light emitting aperture.Downlights are usually recessed into the ceiling so they direct all of their light outputdownward. They are widely used in shops, hotels and other places where a lighting installationwith a discreet appearance is desired. Many different light sources can be used in downlights,the most common being incandescent, tungsten halogen, compact fluorescent and metal halide.Through the use of reflectors, louvres, lenses and refractors many different beam spreads andbeam sizes are possible (see Section 4.3.2). Some downlights allow for adjustable aiming whichis useful when the intention is accent lighting. A number of downlights are fitted withdecorative elements directly beneath the downlight aperture to give an impression of brightnessto the luminaire. The most common problems with lighting installations using an array ofdownlights to create uniform illumination are poor illuminance uniformity caused byoverspacing and dark ceilings. Care is necessary to avoid a fire hazard when recessingdownlights into an insulated ceiling. Figure 4.13 shows a selection of downlights.

Figure 4.13 Examples of downlights

SpotlightsSpotlights are narrow beam luminaires with beam spreads in the range 5 to 30 degrees. Theyare usually mounted on either a base plate or lighting track. When track mounted, spotlightscan be obtained for operation at mains voltage, low voltage or extra low voltage, the latterrequiring the installation of a step-down transformer. Spotlights are widely used in shops,hotels and museums for accent lighting. Spotlights are available that use incandescent, tungstenhalogen, metal halide and extra high pressure sodium light sources of small physical size. Someincandescent and tungsten halogen light sources can be used as spotlights themselves becausethey have reflectors giving the desired beam spread built in. Other light sources have to usereflectors to attain optical control. Filters mounted in front of the spotlight can be used tochange the light colour. Irises and baffles mounted in front of the spotlight can be used tomodify the beam shape. Care is necessary when using spotlights to avoid glare to passers by.Figure 4.14 shows a selection of spotlights.

Figure 4.14 Examples of spotlights


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sWall washersWall washers are asymmetric luminaires with beam spreads up to 130 degrees. They are usuallymounted on either a base plate or lighting track. As their name implies, wall washers are usedwhere it is required to wash a large area with light, evenly. Point and extended light sources canbe used in wall washers, typically tungsten halogen and fluorescents. Wall washers requirecareful aiming to achieve their best effect. Figure 4.15 shows an example of a wall washer.

Figure 4.15 Example of a wall washer

Task lightsTask lights are a necessary part of a task/ambient lighting system. They provide local lighting ofa specific area by bringing the light source closer to the task. The value of task lights is that theyenable the user to have some control of the amount and distribution of light on the task byswitching or dimming the light source and by changing the position of the luminaire relative tothe task. Typically, the light sources used in task lights are incandescent, tungsten halogen orcompact fluorescent. The degree of adjustment available can vary widely as can the amount ofdesk space taken. When selecting task lights attention should be given to the coverage area forcommon positions and the likelihood of glare to the user. Figure 4.16 shows a selection of task lights.

Figure 4.16 Examples of task lights


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4.2.2 Exterior lightingRoad lighting luminairesRoad lighting luminaires used for lighting traffic routes are designed to deliver light to a road sothat the surface is seen to be of uniform luminance and objects on the road can be seen insilhouette. The light distribution is therefore dependent on the position of the luminaire relativeto the road. Most road lighting luminaires are mounted on columns placed at regular intervals atthe side of the road or between crash barriers in the median. A few installations use a catenarysystem in which the luminaires are suspended over the median in a continuous series. Forconflict areas and subsidiary roads (see Chapter 16) the luminaires are designed with a wide lightdistribution so as to give a uniform illuminance across the road. The light sources used in roadlighting luminaires are typically low pressure sodium, high pressure sodium or metal halide. Roadlighting luminaires are often provided with adjustable lamp holders and/or reflectors so as toallow the light distribution to be optimised for the light source and road layout. Two broad classesof road lighting luminaire are semi-cutoff and full cutoff (see Section 4.3.2, Table 4.9) theseclasses reflecting a different balance between luminaire efficiency and the control of glare. Roadlighting luminaires need protection against dust and moisture and so are classified according tothe IP system (see Section 4.3.2, Table 4.10). They are almost always fitted with a photoelectriccontrol package. Figure 4.17 shows a selection of road lighting luminaires.

Figure 4.17 Examples of road lighting luminaires

Post topsPost top luminaires are a form of road lighting luminaire but unlike the road lightingluminaires described above, which are intended for the lighting of high speed traffic routes,post top luminaires are intended for urban areas, where pedestrians are considered as importantas drivers and the decorative aspect of the luminaire is as important as the functional. Post topluminaires are available with either rotationally symmetric or road lighting light distributions,so that the same luminaire can be used to light both roads and open pedestrian areas in a city.Post top luminaires take many different forms, some mimicking traditional styles for historicareas, while others represent the latest design trends. Because of their use in urban areas, lowpressure sodium light sources are not used in post top luminaires, the most common lightsources being high pressure sodium, metal halide, compact fluorescent and induction lamps.Post top luminaires need protection against dust and moisture and so are classified according tothe IP system (see Section 4.3.2, Table 4.10). Because of their relatively low mounting heights,post top lanterns are often constructed of materials that resist attacks by vandals. They arealmost always fitted with a photoelectric control package. The most common problem withpost top luminaires is glare. This problem can be avoided if there is no direct view of the lightsource. Figure 4.18 shows a selection of post top luminaires.


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Figure 4.19 Examples of secondary reflector luminaires

FloodlightsFloodlights can be used to wash a large surface with light or to pick out a specific feature of abuilding. Floodlights vary enormously in their size, power and light distribution. The smallestfloodlights consist of little more than a 150 W linear tungsten halogen lamp with a spreadreflector. The largest consist of a high intensity discharge lamp with power in the kilowatt rangeand a carefully shaped reflector. The light distribution of a floodlight can be rotationallysymmetric, symmetrical about one axis or asymmetrical about one axis. This distribution isusually classified as narrow, medium or wide beam (see Section 4.3.2, Table 4.8). The lightsources used in floodlights include incandescent, tungsten halogen, high pressure sodium andmetal halide. Floodlights need protection against dust and moisture and so are classifiedaccording to the IP system (see Section 4.3.2, Table 4.10) and are often soundly constructed ofmaterials that resist attacks by vandals. Filters mounted in front of the floodlight can be used tochange the light colour. Barn door baffles mounted on the floodlight can be used to modify thebeam shape. Care is necessary when using floodlights to avoid glare to passers by. Figure 4.20shows a selection of floodlights.

Figure 4.18 Examples of post tops

Secondary reflectorsSecondary reflector luminaires are designed for use in pedestrianised places such as city squaresand parks. In this luminaire, light is directed up from the light source in or on the column andthen distributed from a large surface at the top of the column. By changing the area and tilt ofthe reflecting surface, the light distribution can be altered. Secondary reflector luminaires areinevitably inefficient compared to post top luminaires, but they do not cause glare, are not easilydamaged by vandals and can provide a pleasing ambience. Figure 4.19 shows two secondaryreflector luminaires.


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Figure 4.20 Examples of floodlights

WallpacksAs their name suggests, wall packs are designed to be mounted on walls so as to provide a lowlevel of illumination in the nearby area. They are widely used for security and amenity lighting.The light distribution is usually wide and is achieved by a combination of reflecting andrefracting elements. The light sources used in wall packs are usually low wattage low pressuresodium, high pressure sodium and compact fluorescent. Wallpacks need protection against dustand moisture and so are classified according to the IP system (see Section 4.3.2, Table 4.10).Because of their relatively low mounting heights, wallpacks should be solidly constructed ofmaterials that resist attacks by vandals. The most common problem experienced with wallpacksis glare. This problem is much reduced if there is no direct view of the light source. Figure 4.21shows a selection of wallpacks.

Figure 4.21 Three examples of wallpacks

4.3 Certification and classification

4.3.1 CertificationThe principal EU Directives for electrical products are the Electro-Magnetic Compatibility(EMC) Directive and the Low Voltage (LV) Directive, summarised for lighting products inTable 4.3. The LV Directive and the EMC Directive both require products put on the EUmarket to be safe: Compatibility being designated by the CE mark. Products complying withspecified Euronorm (EN) safety standards are presumed to comply. EN standards are basedupon existing international standards, e.g. an IEC standard. For a list of current EN standardsrelevant to lighting products see Tables 4.4 and 4.5 (EMC and Safety), and Table 4.6(Performance). In most instances, there is an equivalent British Standard (BS), known as a BSEN. (For established products a compatible BS may still be used, but preference should begiven to the EN.)

Electrical EN standards are issued by the EU sponsored organisation, CENELEC. They aretype tests, and manufacturers are required to associate them with controls for conformity of production.


XX

LV Directive

From 1 January 1997

Applies to:Luminaires

Lighting componentsLamps

EN safety standardsTable 4.5

EMC Directive

From 1 January 1996

Applies to: (see Table 4.4)

EN standardsTable 4.4

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Table 4.3 EU Directives and lighting products

The EMC and LV Directives, in conjunction with the CEMarking Directive, require complying products to beaccompanied by the CE-mark. CE represents ConformityEuropean. The CE-mark should preferably be on both productand packaging. Responsibility for marking rests on the personputting the product on the EU market.

It is important to note that CE-marks on components do notimply that a luminaire complies. The luminaire as a whole mustcomply and carry the CE-mark. Further, if a luminaire ismodified for use in the EU (e.g. with emergency lighting) themodifier takes over responsibility and must make a new CEmark. A lighting product outside the LV Directive (e.g. an ELVproduct) comes under the General Products Safety Directive.

The ENEC mark indicates independent confirmation that theproduct complies with all relevant EN safety standards and,where available, EN performance standards. (Note: the ENECmark is not applicable to lamps or emergency luminaires). TheENEC mark is not obligatory. Testing and approval are carriedout by national Certification Bodies, e.g. in the UK by BSI. TheXX in the diagram is replaced by a number from 01 to 17, e.g.12 for the UK. The ENEC mark of each of the CertificationBodies is valid throughout the EU. Again, it is important tonote that ENEC marks on components do not imply that aluminaire has an ENEC mark. Further, if a luminaire ismodified the modifier must remove the ENEC mark.

UK enforcing authorities

Trading Standards OfficersHM Revenue and Customs


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BS EN

BS EN 61000-3-2

BS EN 55016

Product

Disturbance in supply system

Luminaires with control gearControl gear

Lamps with integral control gear

Radio frequency interference (up to 30 MHz)

Luminaires with control gearControl gear

Lamps with integral control gear

Immunity

Luminaires with electronic control gearControl gear with electronics

Lamps with integral electronics

(electro-magnetic control gear deemed to comply)

Table 4.4 EN standards and lighting products (CE-mark and EMC Directive)

EN

EN 60555-2EN 61000-3-2

EN 55015

EN 50081 & 2EN 61547

CE-mark

MMM

MMM

MMM

Notes for Tables 4.4, 4.5 and 4.6M = CE-mark obligatory (LV Directive)S = ENEC mark optional (safety standard only available)SP = ENEC mark optional (to safety standard and performance standard)V = Older standard, still valid n/a = Not applicable

Associated standards: BS EN 40 Lighting columns; BS EN 60730–2–3 Thermal protectors for ballasts.The EN standards are based on IEC standards, and their numbers are the IEC numbers plus 60,000; for example EN 60570 = IEC 570. BS EN standards have the EN number.BS EN 60598–2 is linked to BS EN 60598–1


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sTable 4.5 EN Safety standards for lighting products (CE mark and LV Directive)

Note: ‘X’ identifies luminaire types as follows: 1 General purpose, 2 Recessed, 4 Portable, 5 Floodlights, 6 With transformer, 7 Portable – garden, 8 Handlamps, 9 Photo – amateur, 17 Stage and studio, 18 Swimming pools, 19 Air-handling and 20 Lighting chains

Product

Luminaires

Track systems

Street lighting

Emergency

Others (see X)

Ballasts

For fluorescent – Safety

For discharge – Safety

DC electronic – Safety

AC electronic – Safety

Transformers

Electronic stepdown – Safety

Isolating

Neon

Starters/Ignitors

Electronic starters – Safety

Glow starters

Capacitors

For lamp circuits – Safety

Lampholders

Edison screw

Fluorescent lamp & starter holders

Bayonet

Lamp caps and holders

Lamp caps and holders (V)

Lamps

GLS

Tungsten halogen – Domestic

Double capped fluorescent

Single capped fluorescent

CFL Integral – Safety


Low pressure sodium

High pressure mercury

Metal halide

Double capped fluorescent (V)

Single-capped fluorescent (V)

BS EN

BS EN 60570

BS EN 60598–2–3

–

BS EN 60598–2–X

BS EN 60920

BS EN 60922

BE EN 60924

BS EN 60928

BS EN 61046

BS EN 60742

–

BS EN 60926

–

BS EN 61048

BS EN 60238

BS EN 60400

BS EN 61184

BS EN 60838

BS EN 60061

BS EN 60432–1

BS EN 60432–2

BS EN 61195

BS EN 61199

–

BS EN 60662

BS EN 60192

–

BS EN 61167

BS EN 60081

BS EN 60901

EN

EN 60570

EN 60598–2–3

EN 60598–2–22

EN 60598–2–X

EN 60920

EN 60922

EN 60924

EN 60928

EN 61046

EN 60742

EN 61050

EN 60926

EN 60155

EN 61048

EN 60238

EN 60400

EN 61184

EN 60838

EN 60061

EN 60432–1

EN 60432–2

EN 61195

EN 61199

EN 60968

EN 60662

EN 60192

EN 60188

EN 61167

EN 60081

EN 60901

CEmark

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

M

Compatible BS

–

–

BS 4533–102–22

–

–

–

–

–

–

–

–

–

BS 3772

–

–

–

–

–

–

–

–

–

–

BS 7173

–

–

BS 3677

–

–

–

ENECmark

S

S

n/a

S

SP

SP

SP

SP

SP

S

S

SP

S

SP

S

S

S

S

S

n/a

n/a

n/a

n/a

n/a

n/a

n/a

n/a

n/a

n/a

n/a


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Table 4.6 EN Performance standards and lighting products

Compat. BS

–

–

–

–

–

–

–

BS 161

BS 1075

–

Product

LuminairesNo performance standard at present

Photometry – see EN 13032–1

Ballasts

For fluorescent – Performance

For discharge – Performance

DC electronic fluorescent – Performance

AC electronic fluorescent –Performance

Transformers

Electronic stepdown – Performance

Starters/ignitors

Electronic starters – Performance

Capacitors

For lamp circuits – Performance

Lamps

GLS

Tungsten halogen (non-vehicle) (V)

CFL integral – Performance

EN

EN 60921

EN 60923

EN 60925

EN 60929

EN 61047

EN 60927

EN 61049

EN 60064

EN 60357

EN 60969

BS EN

BS EN 60921

BS EN 60923

BS EN 60925

BS EN 60929

BS EN 61047

BS EN 60927

BS EN 61049

BS EN 60064

BS EN 60357

BS EN 60969

EN EC mark

SP

SP

SP

SP

SP

SP

SP

n/a

n/a

n/a


4.3.2 ClassificationGeneral lighting for interiors — luminous flux distributionLuminaires for general indoor lighting are classified by the CIE according to the percentage of thetotal luminous flux emitted above and below a horizontal plane through the luminaire (Table 4.7).

Table 4.7 CIE classification of general indoor luminaires

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Spotlights — luminous intensity distributionSpotlights are characterised by their tight beam control. Most have a rotationally symmetricluminous intensity distribution. The most common way of classifying spotlights is by their beamspread. The beam spread of a spotlight is the angle over which the luminous intensity is 50 percent or more of the maximum luminous intensity in the beam.

It is important to note that beam spread, expressed in this way, is not a good indication of theappearance of the beam. A better classification of the appearance of the beam is the beam size.The beam size is derived from the distribution of illuminance across a uniformly reflectingsurface at a given distance from the spotlight. This distribution is differentiated to obtain theilluminance gradient. The locations of the peaks in the illuminance gradient distribution definethe edges of the beam. The beam size is given as the angle subtended at the spotlight by thedistance between the two edges and is expressed in degrees. The magnitude of the peaks in theilluminance gradient profile indicate the sharpness of the edge of the beam; the higher the peaks, the sharper is the edge of the beam.

Floodlights — luminous intensity distributionFloodlights are classified according to their beam spread. The beam spread is the angle overwhich the luminous intensity drops to a stated percentage of the maximum, usually 50 percent or10 percent. For a floodlight having a rotationally symmetric luminous intensity distribution, onlyone figure is necessary to specify the beam spread. For a floodlight with an asymmetricalluminous intensity distribution, as is usual with rectangular floodlights, two beam spreads areneeded, one for the vertical plane and one for the horizontal plane. If the luminous intensitydistribution in either of these planes is itself asymmetrical relative to the beam axis, two angles are given for that plane and one for the other plane. A simple classification of beam spreads issometimes used (Table 4.8).

Table 4.8 Floodlight beam spread classification

Percentage of total luminous fluxemitted below the horizontal

90–100

60–90

40–60

10–40

0–10

Luminaire class

Direct

Semi-direct

General (diffuse)

Semi-indirect

Indirect

Percentage of total luminous fluxemitted above the horizontal

0–10

10–40

40–60

60–90

90–100

Luminaire classification

Narrow beam

Medium beam

Wide beam

Beam spread at 50 percent ofmaximum luminous intensity

< 20°

20° to 40°

> 40°


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Road lighting luminaires — luminous intensity distributionRoad lighting luminaires have traditionally been classified as full cutoff or semi-cutoff,according to their luminous intensity distribution. BS EN 13201: Part 2: 2003 has introduced a finer classification designed to give better control of disability glare and obtrusive light. This classification uses the maximum luminous intensity per 1000 lamp lumens at differentangles from the downward vertical in any direction as a criterion. Table 4.9 shows the limits for each of the six classes (G levels) and their relationship to the traditional semi-cutoff and full cutoff terms.

Table 4.9 BS EN 13201: Part 2: 2003 road lighting luminaire classification

Operating conditionsThe International Protection (IP) system classifies luminaires according to the degree ofprotection provided against the ingress of foreign bodies, dust and moisture. The degree ofprotection is indicated by the letters IP followed by two numbers. The first number indicatesthe degree of protection against the ingress of foreign bodies and dust. The second indicates theprotection against the ingress of moisture. Table 4.10 shows the degree of protection indicatedby each number. Using Table 4.10 it can be seen that a luminaire classified as IP55 is dustprotected and able to withstand water jets.

Other requirements

None

None

None

0 at greater than 95°



Cutoff classification

Semi-cutoff

Full cutoff

G level

G1

G2

G3

G4

G5

G6

Maximumluminous

intensity/1000lamp lumens,

at 70° fromdownward

vertical

-

-

-

500

350

350

Maximumluminous



vertical

200

150

100

100

100

100

Maximumluminous



vertical

50

30

20

10

10

0


Secondnumber

0

1

2

3

4

5

6

7

8

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sTable 4.10 IP classification of luminaires according to the degree of protection against foreign bodies, dust and moisture

Electrical protectionLuminaires are also classified according to the protection they provide against electric shock.Table 4.11 shows the luminaire classes in the IEC classification.

Firstnumber

0

1

2

3

4

5

6

Degree of protection

Not protected

Protected against solidobjects greater than 50 mm

Protected against solid objects greater than 12 mm

Protected against solidobjects greater than 2.5 mm

Protected against solidobjects greater than 1.0 mm

Dust-protected

Dust-tight

Degree of protection

Not protected

Protected against dripping water

Protected against dripping waterwhen tilted up to 15 degrees

Protected against spraying water

Protected against splashing

Protected against water jets

Protected against heavy seas

Protected against the effects of immersion

Protected against submersion to a specified depth


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FlammabilityThe temperature of a luminaire may limit the surfaces on which it can be mounted. If thesurface is non-combustible, then any luminaire may be mounted on it. But when the surface iseither normally flammable or readily flammable, restrictions may apply. A normally flammablesurface is one having an ignition temperature of at least 200 ˚C and that will not deform orweaken at this temperature. A readily flammable surface is one that cannot be classified asnormally flammable or non-combustible. Readily flammable materials are not suitable fordirect mounting of luminaires. The IEC recommends a two part classification system. Forluminaires suitable for direct mounting only on non-combustible surfaces, a warning noticemay be required. For luminaires suitable for direct mounting on normally flammable surfaces a symbol consisting of a letter F inside an inverted triangle is required.

F

Degree of electrical protection

A luminaire having functional insulation, but no double insulationor reinforced insulation throughout, and without provision for

earthing. This type of luminaire is not permitted in the UK.

A luminaire having at least functional insulation throughout andprovided with an earthing terminal or earthing contact, and, forluminaires designed for connection by means of a flexible cableor cord, provided with either an appliance inlet with earthing

contact, or a non-detachable flexible cable or cord with earthingcontact and a plug with earthing contact

A luminaire with double insulation and/or reinforced insulationthroughout and without provision for earthing

A luminaire designed for connection to extra-low voltage circuitsand which has no circuits, either internal or external which

operate at a voltage greater than extra-low safety voltage

Luminaire class

0

1

2

3

Table 4.11 The classification of luminaires according to the degree of electrical protection


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Chapter 5: Electrics

5.1 Control gear

A wide range of lamps require control gear of some kind to ensure correct running and, insome cases, starting of the lamp. With discharge lamps it is the job of the control gear to limitthe current through the lamp whereas with some incandescent lamps the gear is there to reducethe voltage. Some low voltage tungsten lamps need units to supply them with the correctvoltage and LEDs need electronics to limit the current going through them.

5.1.1 Ballasts for discharge light sourcesGeneral principlesControl gear for discharge lamps has to perform a number of functions:

limit and stabilises lamp current: due to the negative resistance characteristic of gas discharge lamps (see Section 3.1.2) it is necessary to control the current in the lamp circuit

ensure that the lamp continues to operate despite the mains voltage falling to zero at the end of each half cycle

provide the correct condition for the ignition of the lamp: this generally requires the gear to provide a high voltage and in the case of fluorescent lamps requires a heating current to be passed through the electrodes.

As well as these basic functions control gear may also have the following requirements placedon it:

ensure a high power factor

limit the harmonic distortion in the mains current

limit any electromagnetic interference (EMI) produced by the lamp and ballast

limit the short-circuit and run up currents to protect the lamp electrodes and to help the supply wiring system

keep the lamp current and voltage within the specified limits for the lamp during mains voltage fluctuations.

With electromagnetic control gear several separate control components may be needed — thesemay include ballasts, starters, igniters, capacitors and filter-coils.

When electronic control gear is used it is common to integrate all the components into onepackage. The details of the various circuits used are discussed in the following sections.

Electromagnetic control gear for fluorescent light sourcesChoke coils used to be the most common type of current limiting device used with linear andcompact fluorescent lamps. The most common circuit is the switch start, see Figure 5.1.


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Figure 5.1 Schematic diagram of a fluorescent lamp operated using a choke ballast and a switch start

The choke ballast is made from a large number of windings of copper on a laminated iron core.It works on the self-inductance principle and is designed so that impedance of the choke limits thecurrent through the circuit to the correct value for a given lamp and supply voltages. A range ofballasts is available for different lamps and different voltages. Also the ballast design has to bechanged if it is to operate at a different mains supply frequency.

To start the lamp it is common to use a glow starter. The glow starter switch consists of one ortwo bi-metallic strips enclosed in a glass tube containing a noble gas. The glow starter is connectedacross the lamp so it is possible for a current to pass through the ballast, through the electrode atone end of the lamp, through the electrode at the other end of the lamp and back to neutral.When the mains voltage is first applied to the lamp circuit, the total mains voltage appears acrossthe electrodes of the starter and this initiates a glow discharge. This discharge heats the bi-metallicelements within the starter and as the electrodes heat up they bend towards each other untileventually they touch. While the electrodes are touching the current passing through the lampelectrodes pre-heats them. While the electrodes in the starter are touching there is no glowdischarge and so the electrodes cool and separate. At the moment that the electrodes come apartthe current through the ballast is interrupted causing a voltage peak across the lamp. Note: theglow starter does not always create the conditions for the lamp to start and sometimes the startingcycle has to be repeated a number of times. Figures 5.2 to 5.4 illustrate the starting process.

Figure 5.2 The heat from thedischarge in the starter causes the bi-metallic electrodes to bend together

Figure 5.4 The electrodes cooland separate, causing a voltage peakwhich ignites the lamp

S

0

La

B

Figure 5.3 The bi-metallic electrodes touch and a current flows through the circuit preheating the electrodes of the lamp

La = LampB = BallastS = Switch


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ctricsIn addition to the ballast and the starter most fluorescent lamps circuits have a capacitorconnected across the supply terminals to ensure a high power factor for the circuit.

Electromagnetic control gear for HID light sourcesThere are a number of different types of circuits used for high intensity discharge (HID) lamps;they vary according to the type of lamp and its requirements for starting.

The most common type of ballast used is a choke or inductive ballast in series with the lamp.The choke, which is a coil of copper wire wound on a laminated iron core, limits the currentthrough the lamp. Figure 5.5 shows a typical circuit using a choke.

Figure 5.5 Schematic diagram of a HID lamp circuit using a choke

This type of circuit is used for all high intensity discharge lamps apart from the low pressuresodium lamp. The low pressure sodium lamp has a long run-up during which time the voltageacross the lamp needs to be greater than normal mains voltage; this has given rise to a numberof circuits for running the lamp that provide the necessary voltage. The most common of thesecircuits is the autoleak transformer (Figure 5.6).

Figure 5.6 Schematic diagram of a low pressure sodium lamp circuit using an autoleak transformer

B

0

La+

+ –

–

–+

La = LampB = BallastC = Capacitor

N

L

C

BLa

La = LampB = Ballast


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The autoleak transformer works like an autotransformer increasing the supply voltage, but bycareful design of the secondary winding it can also act as a choke to control the current throughthe lamp.

Most high pressure sodium lamps and metal halide lamps require a high voltage pulse to startthe arc in the lamp. This is usually provided by an electronic ignitor. There are several types ofignitor circuits, the two most common are the semi-parallel and the superimposed pulse type(Figures 5.7 and 5.8).

Figure 5.7 A semi-parallel ignition system

Figure 5.8 A superimposed ignition system

The semi-parallel ignitor relies on the tapped ballast coil to generate the ignition pulse whereasthe superimposed type ignitor has its own coil to generate the pulse. The semi-parallel hasmany advantages in that it consumes no power when the lamp is running, it is cheaper andlighter but, as it relies on the ballast, it may only be used with the ballast for which it has beenspecifically designed.

Ignitors sometimes have other features built in such as self-stopping ignitors that will notcontinually try to restrike a lamp that has come to the end of its life. There are also some thatare designed to produce extra high voltages that can restrike hot lamps.

Electronic control gear for fluorescent light sourcesOperating fluorescent lamps at high frequency has a number of advantages (see Section 3.3.3)and most modern control gear is now of this type. Most electronic ballasts for fluorescent lampsare integrated into a single package that performs a number of functions. These functions are:

a low pass filter: this limits the amount of harmonic distortion caused by the ballast, controls the amount of radio frequency interference, protects the ballast against high voltage mains peaks and limits the inrush current

the rectifier: this converts the AC power from the mains supply into DC

a buffer capacitor: this stores the charge from each mains cycle thus providing a steady voltage to the circuits that provide the power to the lamps

L

N

CLa

La = LampB = BallastC = Capacitor

B

L

N

B

La = LampB = Ballast

La


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ctricsthe HF power oscillator takes the steady DC voltage from the buffer capacitor and using semi conductor switches controlled by the ballast controller creates a high frequency square wave

the output of the power oscillator is fed through a small HF coil that acts as a stabilisation coil to the lamp.

Figure 5.9 shows the main components in typical HF fluorescent lamp ballast

Figure 5.9 A circuit diagram of an electronic ballast for two fluorescent lamps

In some ballasts the electronics that control the power oscillator can vary the frequency atwhich the power oscillator runs; as the frequency increases the current passing through thecoils decreases and thus it is possible to dim the lamps. Some types of ballast have a 0 to 10 voltinput that is used to regulate the output while some have digital interfaces. See Section 5.2 forfurther information on controls.

Electronic gear for HID light sourcesMaking electronic control gear for HID light sources is a complex process. There are manydifferent lamp types each with different electrical requirements and a limited range offrequencies in which they can be operated. Also many lamp types do not show a significant gainin efficiency when operated on high frequencies. For these reasons electronic control gear hasbeen developed more slowly for HID lamps than for fluorescent lamps.

However, it is possible to gain a number of benefits from electronic gear for HID lamps. These include:

increased lamp life

elimination of visible flicker

better system efficacy

less sensitivity to mains voltage or temperature fluctuations

the possibility of dimming with some lamp types.

C

C

S1

S2

L

L

L

N

1 2Control

electronics

low passfilter

rectifier buffercapacitor

HF poweroscillator

Lampstabilisation

+–


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Not all these benefits are possible for all lamp types and all control gear combinations. However,the availability and quality of electronic gear available for HID lamps is rapidly increasing.

5.1.2 Transformers for low voltage light sourcesMany tungsten halogen lamps are designed to run on low voltages the most common of which is12 volts. Thus they need a device to reduce the supply voltage. The traditional way to do this wasby using a transformer. Figure 5.10 shows the various currents and voltages in a transformer andgives the approximate relationship between the voltages, currents and the number of turns in theprimary and secondary coils.

Figure 5.10 A circuit diagram for a transformer

As well as reducing the voltage the transformer also isolates the lamp supply from the mains.This means that even under a fault condition the voltage in the secondary circuit will not risesignificantly above the nominal output voltage and so it will always be safe to touch theconductors on the low voltage side.

Most modern transformers for halogen lamps involve electronics. They usually contain highfrequency oscillators to permit the use of smaller transformers that have smaller power losses.With the introduction of electronics it is possible to introduce additional features such asconstant voltage output and soft starting of the lamps.

5.1.3 Drivers for LEDsLEDs need to be run at a controlled current to ensure proper operation. To provide this driversare used. Most drivers take mains power and provide a constant current output.However, it ispossible to control some drivers so that output current is varied so that the LED may bedimmed. In more complex systems it is possible to dim three separate channels separately, sothat when red, green and blue LEDs are used together it is possible to make colour changes.

Most LED drivers can maintain their constant current output over a range of voltages so it isoften possible to connect a number of LEDs in series on one driver.

VpVs

Ip Np : Ns Is

Ep Es

Vp Is Np

Vs Ip Ns= =


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5.2 Lighting controls

5.2.1 Options for controlThere are a number of factors that need to be considered in any control system; these are theinputs to system, how the system controls the lighting equipment and what is the controlprocess that decides how a particular set of inputs will impact on the lighting. Thus for acontrol system to work it must have:

input devices: such as switches, presence detectors, timers and photocells

control processes: these may consist of a simple wiring network through to a computer based control system

controlled luminaires: the system may control luminaires in a number of ways, from simply switching them on and off to dimming the lamp and in more complex systems causing movement and colour changes.

5.2.2 Input devicesManual inputsThese vary from simple switches used to turn the lights on though dimmer switches andremote control units that interface to a control system to lighting control desks that are used intheatres. The point of these units is to allow people to control the lighting and care is alwaysneeded in the application of such devices to ensure that users of the system can readilyunderstand the function of any such control.

Presence detectorsMost presence detectors are based on passive infrared (PIR) detectors, however some devicesare based on microwave or ultrasonic technology. PIR devices monitor changes in the amountof infrared radiation that they are receiving. The movement of people in a space will bedetected by them and this can be signalled to a control system. Thus, if a device detects thepresence of a person this can be used to signal the control system to switch the lights on, but ifthe device has not detected anybody for some time this can be used to signal that there isnobody there and that the lights can be turned off.

TimersMost computerised control systems have timers built in so that they can turn the lighting on oroff at particular times. However, there are also a large number of time switches available thatcan turn lamps on an off at given times. There are also timers used in street lighting that change the time that they switch at throughout the year so that the lamps are switched at dawn and dusk.

PhotocellsThere are many different types of photocell used to control lighting. The simplest to use arethose which switch on at one illuminance value and switch off at another; these are commonlyused to turn exterior lights on at dusk and off at dawn. Some photocells communicate theilluminance value to the central control system, which uses the information to adjust thelighting in some way. Some photocells are mounted on ceilings with shields around them sothat they only receive light reflected from the working plane, this makes them act likeluminance meters and provided the reflectance of the working plane remains constant they canbe set up to follow the illuminance of that plane.


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5.2.3 Control processes and systemsIn the case of simple control systems these are generally configured as some form of automatedswitching in the power supply to a luminaire or group of luminaires. However, more complexsystems are generally configured as a network of devices including luminaires, sensors andcontrol inputs. In most systems the devices are physically connected using some form of cablednetwork but, in principle, devices can be controlled using wireless or infrared communication.

There are several systems in common use for lighting systems and care needs to be taken tospecify the correct type for each component in the system. Two of the most common systemsavailable are DALI and DMX 512.

The basic specification for DALI systems is contained in BS EN 60929: 2006: AC-suppliedelectronic ballasts for tubular fluorescent lamps — Performance requirements. The DALI system is largelyused for lighting systems in buildings but has been extended so that it can be used more widely.It controls luminaires via the ballast used to control the lamps. The system is designed to runup to 64 luminaires on one circuit but there are devices that can control a series of differentDALI clusters thus making it possible to control all the lights in a large building.

DMX 512 was designed to control lights and other equipment in the entertainment industry. The system provides 512 channels of control to a series of devices. In a typical spotlight that hasits aiming controlled, three channels may be used, one to dim the luminaire and one for eachaxis of rotation. The system has traditionally been used in theatres but is increasingly beingused in architectural feature lighting where the lighting equipment is more complex. The basicoperating properties of the system are described in ANSI E1.11: USITT DMX512-A:Asynchronous serial digital data transmission standard for controlling lighting equipment and accessories.


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PART 3: APPLICATIONS

Chapter 6: Lighting design

6.1 Objectives and constraints

Lighting design can have many different objectives. Ideally, these objectives are determined bythe client and the designer in collaboration and cover both outcomes and costs (Figure 6.1).The most common objective for a lighting installation is to allow the users of a space to carryout their work quickly and accurately, without discomfort. However, this is a rather limitedview of what a lighting installation can achieve. For traffic routes, the objective of lighting is tofacilitate the safe and rapid movement of vehicles after dark. For urban areas where people andtraffic may come into conflict, safety is the primary concern although the appearance of peopleand buildings is also important. In areas where crime is rampant, lighting can be used toenhance security. Sport facilities are lit at night to encourage their use. Businesses use lightingto promote their brand and attract customers. Most lighting installations have to serve multiplefunctions. When designing lighting it is always desirable to identify all the functions that thelighting is expected to fulfill.

As for constraints, an important aspect of lighting design is the need to minimise the amount ofelectricity consumed, for both financial and environmental reasons. It is also necessary toconsider the sustainability of the lighting equipment. This means using materials that can beeasily replaced and considering to what extent the equipment can be recycled at the end of itslife. The financial costs, particularly the capital cost, are always an important constraint. Noone wants to pay more for something than is absolutely necessary so the designer needs to beable to justify the proposal in terms of value for money.

Figure 6.1 Objectives, outcomes and costs

6.2 A holistic strategy for lighting

A holistic strategy for lighting design is necessary because without it important benefits will belost and money and human resources will be wasted. The starting point is an in-depthconversation with the client and other members of the design team to formulate a design brief.At such a discussion, it will be necessary to address such fundamental questions as what do youwant to see and what do you not want to see, what is the function of the space, what is theproposed architectural style and what is the budget?

Architecturalintegration

Visualfunction

Energyefficiency

Lightingdesign

Visualamenity

Costs (capital andoperating)

Installationmaintenance


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More formally, nine distinct aspects of lighting need to be considered. They are:

legal requirements

visual function

visual amenity

architectural integration

energy efficiency and sustainability

All these aspects will contribute to the success of a design, but they may not all carry equalweight depending on the particular application and situation. Also there is no particular order inwhich they should be considered. The important issue is that all the elements are considered,perhaps more than once, for a satisfactory solution to emerge.

6.2.1 Legal requirementsThere are a number of legal requirements that apply to all lighting installations. Some aregeneral, e.g. the Construction (Design and Management) Regulations. Some are specific aboutthe type and form the lighting that should be provided, e.g. emergency lighting in buildings(see Chapter 8). Others influence lighting design by the limits they place on the type or amountof equipment that can be used, e.g. Building Regulations. Details of the requirements of theConstruction (Design and Management) Regulations can be obtained from the Health andSafety Executive publications. Details of the significance of Part L of the Building Regulationscan be found in SLL Factfile 9: Lighting and the 2006 Building Regulations. It is essential that thedesigner and the client are aware of the relevant legal requirements.

6.2.2 Visual functionThis aspect is related to the lighting required for doing tasks without discomfort. Chapter 2 hasshown how the illuminance incident on the task will affect the level of visual performanceachievable. Recommended illuminances for different tasks are given in the SLL Code for lighting,various SLL Lighting Guides as well as in Part 3 of this Handbook. These values apply to the taskarea and do not necessarily need to apply to the whole working plane.

The traditional way of lighting an interior work place has been a regular array of luminaires. Forthis approach, a minimum task illuminance uniformity (minimum/average task illuminance ≥ 0.7) is recommended. This approach has the benefit that the tasks can be carried out on thehorizontal plane anywhere in the work place.

In some cases the task will have a colour recognition element. In such cases it will be necessaryto use lamps with a high general colour rendering index (CRI). For such tasks it will beappropriate to use lamps with a CRI ≥ 80 but for tasks with a requirement for very good colourdiscrimination, lamps with a CRI ≥ 90 will be necessary.

The human visual system can adapt to a wide range of luminances but it can only cope with alimited luminance range at any single adaptation state. When this range is exceeded, glare willoccur. If a field of view contains bright elements that cause glare it is likely that they will affectperformance or at least cause stress and fatigue which in turn will cause problems.

To avoid this will mean using luminaires and windows that have limited luminances within thenormal fields of view relative to the adaptation level. Glare limits for different tasks are given inthe SLL Code for lighting, various SLL Lighting Guides as well as in Part 3 of this Handbook.

maintenance

costs

photopic or mesopic vision

light trespass and sky glow.


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Although variation in the light pattern is desirable, it has to be seen as meaningful in terms of theapplication and the architecture. To provide random patches of light in an uncoordinated way forno reason other than to provide light variation would be a poor design solution. Acceptableexamples could be highlighting displays within a retail outlet, or a floral display in a hotel lobby.

There are two further areas of visual amenity that need to be considered and these are in thecolour rendering and colour appearance of the lighting. The required colour rendering willdepend on the functions the lighting is designed to fulfill. Where fine colour discrimination isrequired, light sources with a CIE general colour rendering index of at least 80 should be used.Where a natural appearance is required for people and objects, light sources with a CIE generalcolour rendering index of at least 60 and preferably higher should be used. Where such functionsare not important poorer colour rendering light sources can be used. As for colour appearance, alight source with a correlated colour temperature (CCT) ≤ 3000 K will appear warm and if it hasa CCT ≥ 5300 K it will appear cool (see Section 1.4.3). Where on this scale from warm to coolthe colour appearance should be will depend on the nature of the space. In quasi-domesticsituations, such as hotels, a warm colour appearance will be required but in commercial interiorsa CCT of around 4000 K is appropriate as it blends reasonably well with daylight. The designershould be wary of the names applied to light sources as these can be misleading and differbetween manufacturers. The best way to choose colour appearance is through practical trials.

6.2.3 Visual amenity There is no doubt that lighting can add visual amenity to a space which can give pleasure to theoccupants but whether this provides a more tangible performance benefit is uncertain (Boyce,2003). Studies have shown that people respond to the lit appearance of a room on twoindependent dimensions: visual lightness and visual interest (Hawkes et al, 1979, Loe et al,1994, 2000). Visual lightness describes the overall lightness of the space, which is related to theaverage luminance of vertical surfaces. Visual interest refers to the non-uniformity of theillumination pattern or the degree of ‘light and shade’. People prefer some modulation in thelight pattern rather than an even pattern of illumination, the magnitude of the modulationdepending on the application. There is some evidence that visual lightness and visual interestare inversely correlated (Figure 6.2).

Figure 6.2Map showing the possiblelocations of three applicationareas on a schematic diagramlinking subjective impressions of visual interest and visual lightness

Leisure

Commercial

Industrial

Visual lightness (brightness)Low High

Low

Hig

h

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There is still much to learn about design for visual amenity but it would be negligent to ignore it.The best way to develop an understanding of visual amenity is through personal observations andtrial installations.

6.2.4 Lighting and architectural integrationAll elements of a lighting installation contribute to the architecture or the interior design of abuilding. Understanding the space will be important when deciding what sort of lighting is to beemployed. The dimensions, finishes, texture and colour of the materials forming the space andthe appearance of the luminaires, lit and unlit, should be considered if the desired atmosphere isto be achieved.

A good place to start is with the daylighting since the windows and roof lights are a fundamentalelement of the fabric of the building. This means considering the amount and pattern of daylightrequired for the particular application, and hence the size and positions of windows and rooflights. But windows cannot be designed on the basis of the daylighting alone and other visual,thermal, acoustic and privacy issues need to be addressed. Only a few lighting designers getinvolved with daylighting design. This is a pity because only a few architects have the skills todesign an effective and efficient window system, which means that many opportunities are lost.More information on daylighting design can be obtained from the SLL Lighting Guide 10:Daylighting and window design and Chapter 7 of this Handbook.

Once the daylighting has been determined then the electric lighting can be planned. To integrateelectric lighting with the architecture means considering not only its operation with respect tothe daylighting, but the appearance of the luminaires and controls and the way they areincorporated into the fabric of the building, as well as the lighting effect produced. Just as thelight pattern needs to be meaningful with respect to the building use, the lighting scheme needsto be meaningful with respect to the architecture.

6.2.5 Energy efficiency and sustainabilityIt is the responsibility of the lighting profession to use energy as efficiently as possible but at thesame time to provide lit environments that enable people to operate effectively and comfortably.The current estimate for the UK is that approximately 19% of the electricity generated isconsumed by lighting. This amounts to around 64 TW⋅h/annum.

Energy use involves two components: the power demand of the equipment and its hours of use.The lighting industry has worked hard to develop equipment that has reduced the demand forelectricity for lighting by producing more efficient light sources and their related control circuits,as well as more efficient luminaires. Then there are design options to be considered, such as theuse of task/ambient lighting rather than a blanket provision of light by a regular array of ceilingmounted luminaires. The savings for the task/ambient approach have been estimated to be up to 50% (Loe, 2003).

Good energy efficient lighting design is not just about equipment; it is also about the use oflighting. There are many examples where lighting is left on when it is not required. This may bebecause there is inadequate lighting through daylighting or because people are not present andtherefore the lighting is unnecessary. This aspect of lighting design needs a dramatic change inattitude to improve the energy efficiency of all lighting installations. This requires changes tohow the lighting is controlled both manually and automatically as well as how lighting isprovided in terms of the distribution of light, particularly with respect to the daylighting. It is also necessary for the lighting industry and its customers to use equipment that is sustainable.


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nThis means that the materials used are wherever possible from renewable sources and that at theend of life the redundant equipment can be disposed of safely with most of the base materialsbeing recycled.

6.2.6 MaintenanceIt must be recognised that both daylight and electric light within a building will depreciate withtime. To minimise the effect of this a maintenance programme will need to be designed andimplemented. The maintenance programme will also affect the lighting design and the designerwill need to state the maintenance programme on which the design has been based, otherwisethere could be problems when a client is comparing different design proposals. It will also beimportant for the client to be provided with a maintenance schedule so that they know what willneed to be done. Chapter 21 discusses the various factors that need to be considered whendeveloping a maintenance program.

6.2.7 Lighting costsCosts are always a major concern for any project and it is important to consider these before anywork is undertaken. Both the capital cost and the running, or operational, costs must beconsidered at the outset. If the two cost elements are not considered together in terms of life cycle costing, then a solution which has a low capital cost but a high operational cost could bemore costly overall than an installation with a more expensive capital cost but a low operatingcost. A conflict of interests may arise if the two cost elements are paid for from different budgetsor organisations. This can happen with local authority projects. Here the designer needs topresent a balanced view of the options to enable the clients to decide on the best approach.

The capital costs include the cost of the design process, the equipment and the installationprocess, both physical and electrical. It also includes the commissioning and testing of theinstallation. Allowance must also be made for any builders’ work that forms part of the lightinginstallation. Any other costs that are particular to the lighting design need to be included. It isimportant that the capital cost is agreed at an early stage if a lot of time is not to be wasted. Thecapital cost should be challenged if the client’s expectations seem to be unrealistic.

The operational costs include the cost of the electricity consumed, which comprises items such as standing charges, maximum demand charges and electricity unit costs. They will also includethe cost of maintenance, which includes cleaning and relamping throughout the life of theinstallation. In some cases charges may have to be budgeted for the disposal of redundantequipment although this may be borne by the supplier.

6.2.8 Photopic or mesopic visionThe photometric quantities used to characterise lighting are all based on photopic vision (seeSection 1.2). This makes sense for interior lighting where the luminances are usually high enoughto ensure the visual system is operating in the photopic state but there may be problems forexterior lighting. This is because for adaptation luminances below about 3 cd/m2 peripheral visionis operating in the mesopic state (see Section 2.2.2) and exterior lighting often producesluminances below this level. This is a problem because the spectral sensitivity of the peripheralretina changes continually during mesopic vision depending on the adaptation luminance, thepeak sensitivity moving from the 555 nm to 507 nm as the adaptation luminance decreases to thescotopic state. There is no CIE mesopic observer so no system of mesopic photometry. In thissituation, the simplest approach to ensuring good mesopic vision in exterior lighting is to use alight source with a scotopic/photopic (S/P) ratio greater than 1.5. Such light sources providestimulation to both the cone and rod photoreceptors of the retina.


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6.2.9 Light trespass and skyglowLight can be considered a form of pollution. This is implied by the inclusion of light as astatutory nuisance in the Clean Neighbourhoods and Environment Act: 2005. Exterior lightingis the major source of light pollution. Complaints about light pollution from exterior lightingcan be divided into two categories, light trespass and skyglow. Light trespass is local in that it isassociated with complaints from individuals in a specific location. The classic case of lighttrespass is a complaint about light from a road lighting luminaire entering a bedroom windowand keeping the occupant awake. Light trespass can be avoided by the careful selection,positioning, aiming and shielding of luminaires and by operating a curfew system wherelighting is only available during specified times. The Institution of Lighting Engineers (ILE) hasproduced general guidance on the vertical illuminance that should be allowed to fall onwindows, the maximum luminous intensity of any obtrusive light source and a maximumbuilding luminance for floodlighting. These limits are different for different environmentalzones. The idea behind environmental zones is that some locations are more sensitive to lightpollution than others. Table 6.1 shows the four environmental zones identified by the CIE. Thelimits recommended by the ILE for limiting light trespass are given in Table 6.2.

Table 6.1 The environmental zoning system of the CIE

Table 6.2 Maximum vertical illuminance on windows, maximum luminous intensity forobtrusive luminaires and maximum building luminance produced by floodlighting, for fourenvironmental zones

Environmental zone

E1

E2

E3

E4

Zone description and examples of sub-zones

Areas with intrinsically dark landscapes: National Parks, areas of outstanding natural beauty (where roads are usually unlit)

Areas of ‘low district brightness’: outer urban and ruralresidential areas (where roads are lit to residential road standard)

Areas of ‘middle district brightness’: generally urban residentialareas (where roads are lit to traffic route standard)

Areas of ‘high district brightness’: generally, urban areas having mixed recreational and commercial land use with

high night-time activity

Environmentalzones

E1

E2

E3

E4

Maximum verticalilluminance on windows (lx)

Beforecurfew

2

5

10

25

Aftercurfew

1

1

5

10

Beforecurfew

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50

100

100

Aftercurfew

0

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Maximum luminousintensity (cd)

Maximum buildingluminance (cd/m2)

0

5

10

25


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nThe values in Table 6.2 are for general guidance only and may need to be adjusted for specificcircumstances. For example, the criteria given under zone E1 would not preclude theinstallation of lighting to meet health and safety requirements. As for the maximum buildingluminance, this is given to avoid overlighting but should be adjusted according to the generaldistrict brightness. An alternative approach based on limiting light crossing a property’sboundary is the outdoor site-lighting performance (OSP) method (Brons et al, 2008). Thismethod has the advantage that it deals with the site the designer is responsible for and does notrequire detailed knowledge of areas outside the site.

Sky glow is more diffuse than light trespass in that it can affect people over great distances. Skyglow is caused by the multiple scattering of light in the atmosphere, resulting in a diffusedistribution of luminance. The problem this causes is that it reduces the luminance contrast ofall the features of the night sky thereby reducing the number of stars and other astronomicalphenomena that can be seen. Sky glow has two components, one natural and one due to humanactivity. Natural sky glow is light from the moon, planets and stars that is scattered byinterplanetary dust, and by air molecules, dust particles, water vapour and aerosols in theEarth’s atmosphere, and light produced by a chemical reaction of the upper atmosphere withultra-violet radiation from the sun. The luminance of the natural sky glow at zenith is of theorder of 0.0002 cd/m2. The contribution of human activity is produced by light traversing theatmosphere and being scattered by dust and aerosols in the atmosphere. The magnitude of thecontribution of city lights to sky glow at a specific remote location can be crudely estimated byWalker’s Law. This can be stated as

I = 0.01 P d–2.5

where: I = the proportional increase in sky luminance relative to the natural sky luminance, for viewing 45° above the horizon in the direction of the city (e.g. I = 0.1 = 10 percent increase)P = the population of the cityd = distance to the city (km)

This empirical formula assumes a certain use of light per head of population. Experiencesuggests the predictions are reasonable for cities where the number of lumens per person isbetween 500 and 1000 lumens. Sky glow can be reduced by limiting the amount of light usedfor exterior lighting, by using full-cutoff luminaires that have no upward component (see Table4.9) and by adopting a curfew in which the exterior lighting is either extinguished or reduced toa lower level when there are few people using it. For each environmental zone the maximuminstalled upward light output ratio of the luminaires used should be limited as shown in Table6.3. Again, this is general guidance only and may need to be overturned in specificcircumstances. The OSP method (Brons et al, 2008) again provides an alternative and morecomprehensive approach in that it takes the whole installation and covers reflected light as wellas direct upward light.


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Table 6.3 Maximum installed upward light output ratio; luminous flux emitted above thehorizontal plane as a percentage of the total luminous flux emitted by the luminaire

6.3 Basic design decisions

6.3.1 Use of daylightOne of the first decisions to be made when approaching lighting design for interiors is whatrole will daylight play. The role will depend on the building use but the decision should berecorded early on and be part of the brief. The roles may be any one or any combination of the following:

to provide a view out

to provide enough light to work by

to save energy

to provide lighting for particular tasks requiring very good colour rendering

to enhance the appearance of the space by providing meaningful variation in the lighting.

Depending on the primary role or roles of daylight and hence the amount and distribution ofdaylight in the space, the electric lighting will need to be designed as a stand-alone system or as an integrated system.

6.3.2 Choice of electric lighting systemThe selection of the luminaire, light source and control system to be used is an important one if electricity is not to be wasted and an efficient lighting installation achieved.

The first choice to be made will be to determine the technique to be employed. For interiors, the techniques, in order of decreasing energy consumption, can be simplycategorised as:

a general system: providing a uniform illuminance over the whole working plane area

a localised system: using luminaires located adjacent to the workstation to provide the task illuminance, whilst the overall ambient lighting is provided by the spill light fromthe luminaires

Environmental zone

E1

E2

E3

E4

Maximum upward light output ratio (%)

0

5

15

25


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na local lighting system, sometimes called task/ambient: this uses two separate systems that are inter-dependant; a general lighting installation to provide an ambient lighting condition and a desk or partition mounted task light under the control of the occupant and topping up the ambient lighting illuminance to achieve the required task illuminance.

For exteriors, a general system is the usual choice where work is carried out but much greater degrees of non-uniformity are acceptable where the function of the lighting is essentially decorative.

The second decision to be made will be the choice of light source and luminaire. Thecharacteristics of available light sources and luminaire types are set out in Chapters 3 and 4respectively. It is important to appreciate that light sources differ in their luminous efficacy, life,colour properties, run-up and restrike times and in their ability to be dimmed. Luminaires differ in the distribution of light and the efficiency with which they emit the light produced by the light source.

The third choice to be made is the type of control system. Switching luminaires used to be theonly viable approach to take, but now, with high frequency electronic dimmable ballastsdramatically reducing in price, dimming is a realistic option. For interiors, dimming can be used to save energy even when daylight is absent. This is due to the fact that all lighting is designed foraverage maintained illuminance, which provides more light to start with than is required. Whendaylight is present, dimming can be used to balance the electric lighting to the daylight. Forexteriors, switching and dimming can be used to match the lighting to the patterns of use, e.g. a supermarket car park does not need to be completely lit at 3 a.m. Any users at that hour will park near the doors.

There are basically two forms of lighting control systems: analogue and digital (see Section 5.2).Analogue systems typically use a 1–10 volt protocol providing continuously variable dimming. The digital systems most widely used are DALI and DMX512 (see Section 5.2.3). Both alsoprovide continuously variable dimming. The advantages of digital over analogue control are many, one of the most important being the facility to monitor an installation through a two-waycommunication capability. This transfer of information makes preventative maintenance andenergy monitoring possible.

Control systems can provide the facility for individual or group addressing, zoning and scenesetting. The recording of energy consumption is also highly desirable if the installation is toprovide the information for building monitoring required by Part L of the Building Regulations.

Some control systems allow remote monitoring via the internet. This can be of great benefit tocompanies with large building estates, such as the NHS, education authorities, banks, nationalretail chains etc. By monitoring centrally in a region or area, preventative maintenance can beundertaken such as the anticipation of bulk lamp replacement from the hours-run data.

6.3.3 IntegrationIntegration of a lighting installation takes four forms:

integration within the space, architecture, interior design

integration with other services

integration with daylight

integration with the surroundings.


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Integration within the spaceA lighting installation can be visible and express the interior design or it can disappear into thebackground with only its effect being seen. Both approaches rely heavily on attention to detail,Specifically, attention to the appearance of the luminaire, lit and unlit, is necessary for a designthat is intended to express the interior design, while attention to the builder’s work details isrequired if the intention is to hide the luminaires.

The other aspects of the space that can interact with the lighting are the reflectances and coloursof the interior décor. Large areas of low reflectance reduce the amount of inter-reflected light. Ifinter-reflected light is planned to make a significant contribution to the amount of lightdelivered, large areas of high reflectance surfaces are needed. As for surface colour, the extent towhich they interact with the lighting depends on the saturation of the colour and the area itcovers. Large areas of saturated colour can distort the colour of the light delivered. However,spaces without colour can be very uninteresting. The use of saturated colours over small areasprovides some interest without distorting the lighting.

Integration with other servicesMost services like sprinklers, loudspeakers, fire detectors and supply and extract grilles/diffusers have an optimum spacing to cover the area under consideration and lighting to some extent is the same. Creating a ceiling plane that is restful and harmonious to the eyerequires compromise.

Integration with air conditioning systems needs particular care. Luminaires on the ceiling canshort circuit or deflect airflows thereby creating overheating or draughts. Also, the light outputof fluorescent lamps is affected by the ambient temperature. This means extracting hot airthrough luminaires and integrating luminaires into chilled beams needs careful consideration.

Integration with daylightTo integrate electric lighting with daylight requires zoning of the electric lighting according tothe distribution of daylight and a choice between switching and dimming control.

For buildings with perimeter glazing a rough guide to zoning is to divide the floor plate into 3 m wide strips starting at the perimeter. For buildings with a regular array of rooflights, zoningmay not be necessary.

As for switching or dimming, field studies of switching behaviour have shown that, withmanual switching, electric lighting is usually either all on or all off. Switching is almost entirelyconfined to the beginning and end of a period of occupation; people may switch lighting onwhen entering a room but seldom turn it off until they all leave. The year-round probabilitythat an occupant will switch lights on when entering a room depends on the time of day,orientation of the windows and the minimum orientation-weighted daylight factor on theworking area (see Chapter 7).

Figure 6.3 can be used to estimate the likely energy consumption of an electric lightinginstallation when manual switching is used to adjust it to daylight. If the minimum orientation-weighted daylight factor in the room is 1 percent and work starts at 0800 hours, Figure 6.3shows a 60 percent probability of switching on on entering. If the room is continually occupied,we may conclude that 60 percent is the probability that the lighting will be on at any momentduring the working day. Thus for a lighting installation with a load of 3 kW, and a working yearconsisting of 260 days, each of 8 hours, the total annual energy consumption would be 260 × (8 × 0.60) × 3 = 3744 kW⋅h


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Figure 6.3 The probability of electric lighting being switched on at different times of day forlocations with different orientation-weighted daylight factors (from Crisp and Henderson, 1982)

If luminaires are logically zoned with respect to daylight with convenient pull-cord switches forthe occupants to use, each zone can be treated as a separate room. The probability of switchingwill differ from zone to zone, depending on the minimum orientation-weighted daylight factor ineach zone. Figure 6.3 will still be applicable but the minimum orientation-weighted daylightfactor, and consequent energy savings, must be estimated separately for each zone. If switching isto be relatively unnoticeable to the occupants, the proportion of the electric lighting switchedshould not be more than 20 percent of the total task illuminance.

Automatic photo-electric controls can be used to switch electric lighting in response to daylight.Figure 6.4 shows the percentage of a normal working year during which the luminaires would beoff, as a function of the orientation-weighted daylight factor and of the illuminance at which theluminaires are switched; the ‘design’ illuminance. These curves assume that ‘on’ and ‘off ’switching will occur at the same illuminance. Where this is not the case, where the luminaires areswitched off at an illuminance appreciably greater than that at which they are switched on, themean of the two illuminances should be taken as the ‘design’ illuminance.

Figure 6.4 The percentage of theworking year thatelectric lighting will be switched off plottedagainst orientation-weighted daylight factorfor different ‘design’illuminances, assumingan on/off photoelectricswitching system(from Hunt, 1979)

Pro

bab

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of

swit

cho

n(%

)

100

90

80

70

60

50

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10

0

Time

0.5 percent

1 percent

2 percent

5 percent

4 6 8 10 12 14 16 18 20 22

Perc

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100

90

80

70

60

50

40

30

20

10

0

Orientation weighted daylight factor

100 lx

300 lx

500 lx

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0 1 2 3 4 5 6


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Automatic photoelectric controls can also be used to dim the electric lighting in response todaylight. Figure 6.5 shows the percentage of a normal working year during which theluminaires would have to be switched off in order to ensure the energy saving obtainable bycontinuous photo-electric dimming are achieved. It applies to dimmer systems that can controldown to 10 percent light output or less.

Recommendations for daylighting and supplementary electric lighting are given in BS 8206: Part 2.

Integration with the surroundingsFor exterior lighting, the lighting of the surrounding area has an impact on the perception ofthe brightness of the installation. The same installation in rural and urban settings will lookvery bright in the former and dim in the latter. This means that the maintained illuminanceselected needs to be matched to the illuminances of the surroundings if the expectedappearance is to be achieved.

Figure 6.5 The percentage of the working year that electric lighting will be switched offplotted against orientation-weighted daylight factor for different ‘design’ illuminances,assuming a top-up photoelectric dimming system (from Hunt, 1979)

6.3.4 Equal and approvedOne problem that frequently afflicts lighting designers is the substitution of a cheaper luminairefor the one specified in the original design. Such substitutions are usually made in an effort tosave money. Sometimes, substitutions are justified, sometimes they are not. The key todetermining if a substitution is justified is a review carried out by the original designer todetermine if the substitute luminaire is the equal of the originally specified luminaire andapproved to the relevant standards, i.e. if it is equal and approved. The factors to be consideredin the review are the photometric characteristics, the construction and the aesthetics of thesubstitute luminaire. In addition, attention should be paid to the electrical characteristics,conformity to the relevant standards and the impact on maintenance. Further details of theseelements of the review can be found in the joint statement issued by the Society of Light andLighting, the Electrical Contractors Association, the Institution of Lighting Engineers and theLighting Industry Federation in 2004 (Joint statement, 2004).

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Chapter 7: Daylighting

7.1 Benefits of daylight

In the face of increasing energy costs and concern about global warming, there is considerableinterest in using daylight as the major light source in buildings. Unfortunately, there is littlepoint in doing this if daylighting causes problems to the occupants of buildings. The possibilityof daylight causing problems to occupants may seem unlikely given the well established desireof people to have natural light wherever possible, whenever available. However, a short walkaround any city will reveal numerous well-glazed office buildings where the blinds on manywindows are permanently closed (Figure 7.1). Such behaviour demonstrates the existence of afailed daylighting design for at least some people within the building. Nonetheless, unless thereis a good reason why there should be no daylight in the building, daylighting should always be encouraged.

Figure 7.1 A modern office building with extensive glazing and extensive use of blinds

To make the best use of daylight it is first necessary to recognise that daylight can have bothpositive and negative effects on people. The conclusions of an extensive literature review ondaylight (Boyce et al, 2003a) can be summarised as follows:

Physically, daylight is just another source of electromagnetic radiation in the visible range. Physiologically, daylight is an effective stimulant to the human visual system and the human circadian system. Psychologically, daylight and a view out are much desired and, in consequence, may have benefits for human well-being.

The performance of tasks limited by visibility is determined by the stimuli the task presents to the visual system and the operating state of that system. Daylight is not inherently better than electric light in determining either of these factors. However, daylighting does have a greater probability of maximising visual performance than most forms of electric lighting because it tends to be delivered in large amounts with a spectrum that ensures excellent colour rendering.

There can be no guarantee that daylighting will always be successful in maximising visual performance. Daylight can cause visual discomfort through glare and distraction, and it can diminish the stimuli the task presents to the visual system by producing veiling reflections or by shadows. The effectiveness of daylighting for visual performance will depend on how it is delivered.


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People will take action to reduce or eliminate daylight if it causes discomfort or increasestask difficulty.

The performance of both visual and non-visual tasks will be affected by disruption of the human circadian system. To avoid such disruption, the exposure to bright light during the day and little light at night is necessary. Daylighting is a convenient means to deliver bright light during the day to people who have little opportunity to go outside.

Different lighting conditions can change the mood of occupants of a building. However, there is no simple recipe for what lighting conditions produce the most positive mood. Windows are strongly favoured in work places for the daylight they deliver and the view out they provide, as long as they do not cause visual or thermal discomfort, or a loss of privacy. Therefore, the presence of well-designed windows is expected to enhance positive mood and their absence to increase negative mood, although whether it is the view out or the admission of daylight that provides the benefit is unclear.

Exposure to daylight can have both positive and negative effects on health. The strongest effects occur outdoors. Exposure to daylight outdoors can cause tissue damage, which is bad, and generate vitamin D, which is good. Daylight and sunlight delivered through glass will have less ultra-violet radiation than the same radiation outdoors, but can still have adverse effects on people who are sensitive to ultra-violet radiation. Daylighting that makes what needs to be seen difficult to see can cause eyestrain. Conversely, daylighting that makes what needs to be seen easy to see can reduce eyestrain. Windows that provide a view out as well as daylight can reduce stress.

These conclusions imply that good daylighting design is not simple. Thought needs to be givento the amount of daylight available, the view out, the control of glare, the light distribution inthe space, solar heat gain and integration with electric lighting. When done well, daylighting canmake a very effective and attractive space (Loe and Mansfield, 1998; Philips, 2004) but whendone without thought or with thought limited to the external appearance of the building,daylighting can cause discomfort to occupants and add to the energy consumption of the building.

Figure 7.2 An attractive daylighting design


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7.2 Daylight availability

Daylight varies in both amount and spectrum with sun altitude and atmospheric transmission.This means that the availability of daylight will vary with the season of the year and the natureof cloud cover. Figure 7.3 shows how the illuminance on a horizontal plane provided bydaylight varies with the time of year and the time of day. Details on the availability of daylightcan be found in SLL Lighting Guide 10 and Littlefair and Aizlewood (1999)

Figure 7.3 The illuminance on a horizontal plane provided by daylight varies with the time ofyear and the time of day

Of course, these illuminances are measured on an unobstructed horizontal plane. In a building,the amount of daylight available will depend on the position and size of the windows orrooflights. The contribution of daylight inside a room is given by the daylight factor inconjunction with the daylight availability. This can indicate a minimum, a range or an average.The daylight factor is defined as the ratio of the illuminance at a point within a building to theilluminance on an unobstructed horizontal surface at the same position. Daylight factor isusually expressed as a percentage.

For determining the minimum contribution of daylight to an interior, it is usual in temperateclimates like that of the UK to assume the luminance distribution of the sky follows the CIEStandard Overcast Sky. (Figure 7.4) This assumption eliminates sunlight from consideration.For the Standard Overcast Sky, daylight factor is the sum of three components; the skycomponent, the internally reflected component and the externally reflected component (Figure7.5). The sky component is the light that reaches the measurement point directly from the sky.The internally reflected component is daylight that arrives at the measurement point afterreflection inside the room. The externally reflected component is daylight that arrives at themeasurement point after reflection outside the room.

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Figure 7.4 The luminance distribution of the sky follows the CIE Standard Overcast Sky

Figure 7.5 The components of the daylight factor

Daylight factor can be given either as a value at a specific point or as an average over a definedarea like a room (Littlefair, 1991; Littlefair, 1995, Littlefair and Aizlewood, 1999). Computersoftware for estimating point daylight factors which can then be presented as contours oraverage is available.

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gIt is important to appreciate that while daylight factor is useful for identifying the minimumcontribution daylight will make to the illuminance, it is not relevant for determining if visualdiscomfort is likely to occur. Visual discomfort is most likely to occur when either the sun or ahigh luminance part of the sky is visible. Even when examining the minimum contribution thatdaylight can make to the illuminance, it is important to appreciate that, in practice, the daylightfactor will vary with orientation of the window, e.g. in the UK, windows facing south will havehigher values than those facing north. Corrections for window orientation can be applied bymultiplying the daylight factor by a weighting factor to give the orientation-weighted daylightfactor. The weighting factors for north, east, south and west-facing windows are 0.77, 1.04, 1.20and 1.00 respectively.

Daylight requirements for buildings are covered in BS 8206: Part 2 and the SLL Lighting Guide10: Daylighting and window design. Unless the designer has some guidance about the amount ofdaylight preferred or required, the window area may be reduced on the basis of the building’soverall thermal performance.

7.3 Daylight as a contribution to room brightness

In most buildings, users prefer rooms to have a daylit appearance during daytime hours, evenwhen there is significant use of electric light. This appearance can be achieved by ensuring thatthe changing brightness of daylight is clearly noticeable on walls and other interior surfaces.

For a daylit appearance without any electric lighting, the average daylight factor should not beless than 5 percent. For a daylit appearance with the use of electric lighting, the average daylightfactor should be not less than 2 percent. For this condition, daylight will be sufficient for part ofthe year but for others additional electric lighting will be required. In both cases, the surfacereflectances and the positions of windows should be high so that inter-reflected lighting in thespace is strong and even.

In a room where the average daylight factor is less than 2 percent, the general appearance willbe of an electrically lit interior. Daylight will be noticeable only on room surfaces immediatelyadjacent to windows, although the windows may still provide adequate views out for occupantsthroughout the room.

7.4 Daylight for task illumination

Where daylight alone is required to provide the illumination for a visual task, the illuminanceshould not fall below the recommended maintained value during daytime. The illuminanceuniformity within the immediate task area should be similar to that recommended for electriclighting although the illuminance diversity may be greater. This can be determined from thedaylight factors and the daylight availability.

7.5 Types of daylighting

Daylight can be delivered into a building through conventional windows, clerestory windows orrooflights as well as a number of remote distribution systems, such as light pipes.

7.5.1 WindowsWindows have the advantage of providing both daylight to the interior and a view out. Theirdisadvantage is that the amount of daylight delivered to the office decreases dramatically as thedistance from the window increases, although the view out is preserved over a larger distance aslong as there are no major internal obstructions.


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As a rule of thumb, daylight will penetrate to a depth of twice the height of the window headabove the window sill, assuming no external obstruction of the sky. Where there is an externalobstruction the extent of daylight penetration is given by the no-sky line. This is the line on theworking plane beyond which no direct light from the sky will penetrate (Figure 7.6).

Figure 7.6 The extent of direct daylight penetration is given by the no-sky line

The important aspects of windows as far as people are concerned are their size, shape, spectral transmittance and solar shielding.

Desired size and shape are determined by the nature of the view out. Glazed areas of 15 percentor less of the window-wall area and window shapes and layouts that break up the view aredisliked (Keighly, 1973 a and b). Larger windows are liked depending on the nature of the view.

As for spectral transmittance, there are two aspects that need to be considered, the totaltransmittance of light and the colour appearance of the light transmitted. Transmittances aboveabout 40 percent are highly acceptable but as the percentage transmittance decreases, percentageacceptance also decreases (Boyce et al, 1995). There are also limits on the colours of the glassthat are acceptable (Cuttle, 1979). Figure 7.7 shows the dissatisfaction contours for glass to beused in windows for daylighting. It is clear that glass types with chromaticities that depart fromthe central part of the black body locus risk being considered unsatisfactory.

Figure 7.7Percent dissatisfactioncontours for thechromaticity of glazing plotted on the CIE 1931chromaticity diagram(after Cuttle, 1979)

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gWindows also need to be considered in terms of their solar shading because solar shading canhave an impact on both the visual and thermal environment through the admission of sunlight.The impact on the thermal environment is through the heat gain and heat loss of the wholebuilding and, locally, on the likelihood of thermal discomfort caused by overheating due toexcessive thermal radiation (sunlight) or overcooling, due to radiant heat loss to a cold windowor the generation of draughts. Visual and thermal discomfort is unlikely if direct sunlight isexcluded from working areas, although there is a desire for sunlight to be visible in non-working areas. Solar shading can be achieved through fixed features of the building such as lightshelves and adjustable features such as blinds (Littlefair, 1999).

Even when sunlight is excluded from working areas, windows can still be a source ofdiscomfort if bright clouds or sunlight falling on blinds cause high luminance reflections incomputer screens.

Guidance on the design of windows is given in the SLL Lighting Guide 10: Daylighting andwindow design.

7.5.2 ClerestoriesClerestory windows are strictly a narrow strip of windows high up on the wall (Figure 7.8).They may be vertical or sloping. Because of their position, clerestory windows provide deeperpenetration of daylight into the space but little by way of a view out. Clerestory windowsprovide a direct view of the upper parts of the sky so care is necessary to avoid glare.

One way to increase the penetration of daylight even further into the space is to fit prismaticrefractors in clerestory windows instead of conventional glass. The effect of these refractors isto bend the light from the upper sky up onto the ceiling, from where it will be diffuselyreflected. Good quality refractors are required if bright spots on the ceiling are to be avoided.

Guidance on the design of clerestory windows is given in the SLL Lighting Guide 10: Daylighting and window design.

7.5.3 RooflightsRooflights are a glazed opening in the roof of a building. Rooflights can be vertical or sloping(Figures 7.8 and 7.9). Rooflights can be oriented to minimise sun penetration as in thetraditional north-facing monitor roof.

Figure 7.8 Clerestory windows and a rooflight


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The daylight penetration from rooflights can vary widely depending on the design of therooflight and the presence of internal devices to limit sun penetration. Rooflights are a veryeffective way to provide daylight over a large area, single story building.

Figure 7.9Sloping roof lights providingdaylight in a factory

Guidance on the design of rooflights is given in the SLL Lighting Guide 10: Daylighting andwindow design.

7.5.4 AtriaAtria have become an increasingly popular feature of buildings. Atria are often used to light acentral circulation or social area by daylight admitted through a glass roof or wall (Figure 7.10).Atria will provide some daylight to adjacent working areas, but the amount is often small anddoes not penetrate very far. The main function of an atrium is to provide a pleasing visualexperience and a degree of contact with the outside for people in the working areas.

Figure 7.10 An atrium providing plentifuldaylight into a circulation/relaxationarea of an office but limiteddaylight into the working areas

7.5.5 Remote distributionIt is possible to provide some daylight into spaces that have no possibility of windows orrooflights through remote distribution devices such as light pipes. Such systems take variousforms but all collect daylight and sunlight in some way and transmit in through a shaft or pipeby reflection to a distribution point in the space (Figure 7.11).


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gRemote daylight distribution systems are inherently inefficient and the further they have totransmit the daylight and the more convoluted the path, the greater is the inefficiency (Littlefair,1990; Littlefair et al., 1994). The efficiency of many remote distribution systems can also varydramatically from clear to overcast skies. Nonetheless, where there is no other possibility ofproviding daylight to a space, remote distribution systems can be appreciated.

Figure 7.11Internal and externalviews of two light pipeinstallations

7.5.6 Borrowed lightBorrowed light is a term used to describe the lighting of an enclosed internal space through awindow that connects to an adjacent daylit space. Borrowed light rarely brings much daylightinto the internal space but it does provide a connection with the outside and can be usefulwhen the amount of light required in the internal space is less than in the daylit space, e.g. in a corridor.

7.6 Problems of daylighting

Daylighting can cause both visual, thermal and privacy problems.

7.6.1 Visual problemsThe visual problems of daylighting are glare and veiling reflections. Glare is caused by a directview of either the sun or the bright sky. Glare is usually experienced when facing a window in afaçade receiving direct sunlight. Veiling reflections are most commonly experienced whensitting with ones back to a window, when the high brightness impinging on a computer screenreduces the contrast of the display.

The first step in overcoming glare is to ensure that the differences in luminance between thewindow or rooflight and the immediate surroundings are minimised. This can be done eitherby decreasing the luminance of the sky or by increasing the luminance of the window surroundor both. The luminance of the sky can be reduced by fitting tinted, reflective or fritted glass.This can be effective for a bright sky but not for direct sunlight. The downside of such glazingis that it permanently reduces the availability of daylight. As a consequence, the view out canseem dull, particularly with an overcast sky.

As for increasing the luminance of the window surrounds, this means that the glazing barsshould be of high reflectance, the edges of the window or rooflight aperture should be splayedback and the wall or ceiling in which the window or rooflight is installed should be of highreflectance and well illuminated (Figure 7.12). If this is not enough then the solution to boththese problems is the provision of some form of shading device or screening (Littlefair, 1999; Dubois, 2003).


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Shading devices can be either passive or active. Passive shading devices restrict daylight at alltimes, active shading devices do not. Passive shading devices consist of light shelves, overhangsand louvres.

Light shelves are formed by a light reflective surface mounted either internally or externally, partway down a window. They are designed to shade the area near the window and reflect daylightand sunlight up onto the ceiling. This action changes the appearance of the space and balancesthe daylight distribution better. Light shelves do not generally increase the amount of daylight inthe depth of a space by any significant amount. Light shelves need regular cleaning if they are tobe effective. To ensure that parts of the ceiling near the window do not exceed the recommendedmaximum luminance (1,500 cd/m2) and that sunlight does not penetrate directly into thebuilding through the window above the light shelf, it is essential to examine the geometry of thelight shelf in relation to the yearly sun paths.

Structural overhangs shield the windows from areas of high brightness sky and are useful forlimiting building heat gain. However, they will not shield the occupants from the low winter sun.To minimise glare, the underside of overhangs should have as high a reflectance as possible.

For maximum effect, louvres are best located on the exterior of a building (Figure 7.13) wherethey are more effective at controlling solar heat gain. The size and shape of the louvres will beinfluenced by orientation of the building and its latitude. South-facing facades are best protectedwith horizontal elements whilst east and west facades are better protected by using verticalelements angled slightly to the north. Roof lights can be protected by shaped cells where thedimensions will be decided by whether all sunlight is to be excluded at all times (Lynes andCuttle, 1988). Grills are an alternative to louvres for shading a window wall.

Figure 7.12Splayed surround to a skylight

Figure 7.13External louvres


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gActive shading devices, such as louvres and awnings, are located on the exterior of a building.Motorised louvres can be effective at maximising the amount of daylight available, whilstreducing the penetration of the sunlight. Movement of louvres can be distracting. They alsoimpose a maintenance requirement. The same concerns apply to motorised awnings but inaddition, there is a need to sense wind speed so that the awnings can be retracted if necessary.Screening is usually provided by some sort of blind fitted to the window. Blinds can be used toreduce glare and direct radiation but in so doing they may also restrict daylight and view out.Some blind materials, such as perforated fabric, allow a degraded view out to be retained whilelimiting daylight admission.

Others, such as venetian and vertical blinds allow the user to adjust blind coverage and theangle of the blades to preserve a limited view out while restricting the admission of sunlight. Yetothers, such as roller blinds allow the view of the sky to be restricted while preserving a view ofthe ground outside. While such adjustments are possible in principle, in practice human inertiausually means that blinds are adjusted rarely with the consequence that the amount of daylightin the interior is less than expected by the designer (see Figure 7.1). Such inertia can beovercome by using motorised rather than manual blinds linked to sunlight on the façade butthis is expensive and is another maintenance issue. All blinds should have a reflectance of atleast 0.5. Where they are likely to be subject to direct sunlight, blinds should have atransmittance of less than 0.1.

7.6.2 Thermal problemsDaylight admitted to a building represents a heat load. In winter this may be useful but insummer it can represent an additional cooling load. Therefore, when considering the energybalance of the whole building, it is essential to consider the contribution of daylighting. On a local scale, sunlight directly incident on people near a window can cause thermaldiscomfort. This is a good reason for not positioning workplaces close to a window but rather to use this space for circulation. When selecting shading devices, consideration should be given to these effects.

7.6.3 Privacy problemsExtensively glazed buildings can present privacy problems, particularly on the ground floor.Concerns about privacy can lead to blinds being closed at all times with a consequent lack ofdaylight and view out. There is little that can be done about the admittance of daylight but adegraded view out can be preserved without sacrificing privacy by using blinds made fromperforated fabric, particularly when the outside face of the blind is of high reflectance and theinside face is of low reflectance. An alternative solution is to move workplaces away from thewindows and to use this space for circulation.

Recommendations for daylighting and supplementary electric lighting are given in BS 8206: Part 2.

7.7 MaintenanceDirt will build up on the exterior and interior surfaces of windows and rooflights. This willreduce the transmittance of the glass and therefore the amount of daylight entering thebuilding. The degree to which this will occur will depend largely on the inclination of the glassand the air quality of the local environment. A busy urban environment will produce more dirtthan a rural one. To minimise the problem a regular window cleaning programme is needed,which will require easy and safe access to the windows. Without this, window cleaning will beexpensive and is likely that it will not be carried out as often as necessary.


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Chapter 8: Emergency lighting

8.1 Legislation and standards

Emergency lighting is a legal requirement in almost all premises. Details of emergency lightingsystems can be found in SLL Lighting Guide 12: Emergency lighting design guide.

When the normal mains lighting fails in areas without natural light it is necessary to evacuate thepremises, to move people to a place of safety or to allow essential processes to continue or be shutdown. During this period, emergency lighting should be provided from a source independent ofthat supplying the normal lighting.

A number of European Union Directives have implications for emergency lighting. They are:

The Construction Products Directive (89/106/EEC)

The Workplace Directive (89/654/EEC)

The Signs Directive (92/58/EEC).

These Directives have been implemented into UK law. For emergency lighting, this has beenachieved through the Building Regulations: Approved Document B in England and Wales, theBuilding Standards (Scotland) Regulations and associated Technical Standards for Scotland andthe Building Regulations (Northern Ireland) 2000 and Technical Booklet E for Northern Ireland,the Fire Precautions (Workplace) Regulations and the Health and Safety (Safety Signs andSignals) Regulations.

In addition, the responsibility for ensuring safety in fire has now been shifted by the introductionof the Regulatory Reform (Fire Safety) Order 2005, from the fire authorities to any person whoexercises some level of control over premises. This person is required to take reasonable steps toreduce the risk of fire and to ensure that occupants can safely escape if a fire does occur. To meetthese obligations, it is necessary to carry out a risk assessment, create and implement a plan to dealwith an emergency and to document the findings. Guidance is available from BS 5266-10: 2008.

As well as these legal requirements for emergency lighting, standards govern both equipmentdesign and performance and the design of emergency lighting systems. BS EN 60598 is thestandard covering all types of luminaires. Part 2.22 covers emergency lighting luminaires. BS 5499covers the colours, design and layout of emergency signs and is based on the internationalstandards ISO 3864 and 6309. There are numerous product standards covering lamps andindividual components of luminaires. BS 5266 covers design of emergency lighting systems aswell as some specific equipment. It consists of the following Parts:

BS 5266-1: Code of practice for the emergency lighting of premises

BS 5266-2: Code of practice for electrical low mounted way guidance systems for emergency use

BS 5266-3: Specification for small power relays (electromagnetic) for emergency lighting applications up to and including 32 A

BS 5266-4: Code of practice for design, installation, maintenance and use of optical fibre systems

BS 5266-5: Specification for component parts of optical fibre systems


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BS 5266-6: Code of practice for non-electrical low mounted way guidance systems for emergency use. Photoluminescent systems

BS EN 1838, BS 5266-7: Lighting applications. Emergency lighting

BS 5266-8: Emergency escape lighting systems layout (2004) (dual numbered BS EN 50172).

Various standards covering design of lighting schemes make reference to emergency lighting,including BS EN 12464: Lighting of workplaces, BS EN 12193: Sports lighting and BS EN 50172:Emergency escape lighting systems.

8.2 Forms of emergency lighting

Emergency lighting can take several different forms depending on its purpose. Figure 8.1 shows a classification of emergency lighting. The first division is between escape lighting and standbylighting. Escape lighting is designed to ensure the safe evacuation of the space. Standby lighting is designed to enable continued operation of space. Escape lighting is subdivided into the lighting of the escape route, the lighting of open areas where there is no defined escape route and highrisk areas where a hazardous activity takes place and needs to be made safe before evacuation.

Figure 8.1 Classification of emergency lighting

8.2.1 Escape route lightingAn escape route is a clearly defined, permanently unobstructed route equal to or more than 20 m long and up to 2 m wide. The lighting of such routes, or the 2 m strips of wider routes, isspecified in terms of minimum illuminances on the floor, illuminance diversity, glare limits,response times, duration and light source colour rendering. The specific criteria are as follows:

Minimum illuminance on the centre line: 0.2 lx, but preferably 1 lx.

Minimum illuminance on the centre band of the route, consisting of at least 50% of the route width: 0.1 lx, but preferably 0.5 lx.

Illuminance diversity: maximum/minimum illuminance on the centre line < 40.

Maximum luminaire luminous intensity for level routes: see values in Table 8.1. These apply in all directions for angles between 60 and 90 degrees from the downward vertical.

Maximum luminaire luminous intensity for non-level routes: see values in Table 8.1. These apply for all directions within the lower hemisphere.

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Maximum response time: minimum illuminance within 5 s of supply failing (15 s if occupants familiar with place).

Minimum duration: 1 hour.

Minimum light source general colour rendering index: 40.

8.2.2 SignageThe style and details of the safety signs for escape routes are defined in BS 5499 (Figure 8.2).ISO 3864 gives the internationally agreed formats of exit signs and safe condition signs (Figure8.3). The designs consist of a rectangular or square shaped frame with a white pictogram on agreen background. The green area must be more than 50% of the total area of the sign and thecolour must conform to ISO 3864-1. As the pictograms can differ in style and content, it isimportant to consult the enforcing authority for a particular project on its interpretation prior to choosing the signs.

In addition to the design of the sign, there are photometric, geometric, response time andduration requirements for safety signs. These are as follows:

Colour: conform to ISO 3864-1 chromaticity co-ordinates.

Minimum luminance of safety colour: 2 cd/m2.

Luminance diversity: maximum/minimum luminance of colour < 10.

Luminance contrast range: luminance ratio of white to colour > 5 but < 15.

Maximum viewing distance (externally illuminated sign): 100 × mounting height.

Maximum viewing distance (internally illuminated sign): 200 × mounting height.

Minimum mounting height: 2 m above floor.

Minimum response time: 50% of design luminance in 5 s, 100% of design luminance in 60 s.


8.2.3 Open area lightingAn open area is defined as an area of at least 60 m2 which people have to move through beforereaching an escape route. Open areas are divided into two types: those which are unfurnishedor in which the furnishings can be easily reconfigured and those in which the seating is fixed.Examples of the former are open plan offices and covered car parks. Examples of the latter areconcert halls and lecture halls. Signage defining access to escape routes should be visible fromall points in both types of open area.

Figure 8.2 Safety signs for escape routes

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Figure 8.3Exit signs and safe condition signs


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gThe lighting requirements for the open areas which are empty or where the furniture can beeasily reconfigured are as follows:

Minimum illuminance on the empty floor, excluding a 0.5 m wide perimeter band: 0.5 lx.

Illuminance diversity: Maximum/minimum illuminance on the empty floor < 40.

Maximum luminaire luminous intensity: see values in Table 8.1. These values apply in the zone 60 to 90 degrees from downward vertical.

Maximum response time: 50% of minimum illuminance within 5 s of supply failing and 100% within 60 s.



Table 8.1 Maximum luminaire luminous intensity for escape route, open area, fixed seatingarea and high risk area emergency lighting for different luminaire mounting heights

The lighting requirements for fixed seating open areas, which may be raked, are as follows:

Minimum illuminance on a plane 1 m above the floor of the seated area: 0.1 lx.

Illuminance diversity: maximum/minimum illuminance on the plane 1 m above the floor of the seated area < 40.


Maximum luminaire luminousintensity for escape route, open areaand fixed seating area lighting (cd)

500

900

1,600

2,500

3,500

5,000


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Maximum response time: 100% of minimum illuminance within 5 s of supply failing.



8.2.4 High risk areaA high risk area is defined as one where a hazardous activity occurs that has to be made safe orterminated before leaving or where people passing by may be exposed to the hazard, e.g.moving machinery. The presence of a high risk area should be revealed by the risk assessmentrequired by the Fire Precautions (Workplace) Regulations 1997. The lighting requirements forhigh risk areas are as follows:

Minimum illuminance on the task: 10% of the maintained illuminance on the reference plane of the task (see SLL Code for lighting) but at least 15 lx.

Minimum/average illuminance uniformity on the reference plane for the task > 0.1.


Maximum response time: 100% of minimum illuminance within 0.5 s of supply failing.

Minimum duration: period for which the risk exists to people.


8.2.5 Standby lightingIn areas or places where a continuous operation is required during the failure of the supply tothe normal lighting, standby lighting should be installed. An example of such a location wouldbe an operating theatre in a hospital. This system should provide adequate illumination for thevisual tasks as recommended in the Schedule of the SLL Code for lighting. If standby lighting isused for escape lighting, then the escape lighting part should be segregated from the rest of thesystem and should conform to the rules applied to emergency lighting systems.

8.3 Design approaches

Emergency lighting should be considered as an integrated part of the building lighting. Unlessthis is done, there is a risk that the normal lighting and the emergency lighting will clash inappearance to the detriment of the whole scheme.

Emergency lighting can be provided using either self-contained units or a centrally poweredsystem using either batteries or a motor-generator set. A self-contained unit contains its ownpower source and can be a stand-alone luminaire or an emergency version of the normallighting luminaires. Central systems provide power to the emergency light source via separate,protected wiring to slave luminaires.

For small buildings, the most economic solution is nearly always self-contained units. In largebuildings, such as office blocks, factories and shopping centres, the most economic solution isnearly always central battery systems unless a generator is required for other purposes. Thebalance of costs between the options is related to the equipment cost and the wiring cost.Central systems use cheaper luminaires without batteries but have a costly central battery andcharger/inverter or generator and fuel tanks, both requiring segregated protected wiring.


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gThe running costs of central systems are usually lower than those of a system using self-contained luminaires, as only the central unit needs to be monitored whereas self-containedunits need regular servicing and replacement of the battery packs.

8.4 Emergency lighting equipment

8.4.1 Power sourcesSelf contained luminairesSelf-contained luminaires have a secondary sealed battery, a charger (control unit), circuitry(which monitors the mains supply) and a lamp. In the mains-healthy condition, the battery ischarged. In the event of a failure of the mains supply, the battery is connected to the lamp eitherdirectly or via an inverter module. The battery is usually a sealed rechargeable nickel-cadmium,lead acid or nickel-metal hydride type. These batteries are small, with limited storage capacityand life, and are very temperature sensitive. They should conform to IEC 60285, IEC 60896-2or IEC 61056-1 and should provide four years service life. Care will be necessary in their disposal (see Section 21.9).

Central battery systemsCentral battery systems consist of a remotely located power source connected by protectedwiring to slave luminaires. The batteries consist of either vented or sealed lead-acid or nickelcadmium alkaline cells. They have high storage capacity, long life and a wide operating voltagerange. These batteries should conform with BS EN 50171. In addition to the battery, the systemincludes subcircuit monitoring of the supply to normal lighting, and an automatic change-overdevice to connect the slave luminaires to the power supply when the mains supply fails. Thereare three main types of systems.

AC/DC battery powered systems supply direct current from the battery to the emergency slaveluminaires, normally at 24, 50 or 110 V. If a maintained system is required, this is normallyachieved by using floating batteries or by using a transformer to provide the appropriate outputvoltage in the supply healthy condition. Special or modified luminaires have to be used to becompatible with the range of output voltages and the effects of supply-cable voltage drop. These luminaires normally provide higher light outputs than are available from self-containedluminaires.

AC/AC battery powered systems modify the output from the battery by using an inverter tocreate 230/240 V AC. These systems can operate any suitable normal luminaires, which do notneed to be modified, and so they can provide full light output in the emergency condition. Thepower unit has to be matched to the emergency load and be capable of supplying both the totalwattage and VA rating of the load and also providing the full starting surge of the luminaires.Static inverters designed for the application should be compatible with the luminairecharacteristics but caution should be exercised if a system using a general purposeuninterruptible power supply unit (see below) is being designed. BS EN 50171 sets out some important points that need to be checked.

Uninterruptible power supplies (UPS) are a form of AC inverter which continue to providetheir output without a break during a supply failure enabling them to be used with dischargelamps that otherwise would have unacceptably long re-strike times. Because these inverters arenormally used for computer back-up care must be taken to ensure they are correctly engineeredfor emergency lighting use. The UPS must comply with the requirements of BS EN 50091 aswell as BS EN 50171.


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The charger must be capable of recharging the battery to 80% of capacity within 12 hours. Thebattery must be designed for 10 years design life (lower life batteries exhibit a sudden failuremode, which will not be picked up by the emergency lighting testing procedures). The outputmust be capable in the emergency condition of clearing all distribution protection devices andfuses (normally a UPS unit drops down to zero voltage when sensing a distribution shortcircuit). It is important to clear the protection device and re-supply those parts of the buildingthat do not have a fault. The inverter must be capable of starting the load from the battery in anemergency. The system monitors, as defined in BS EN 50171, should be supplied.

GeneratorsThe main components of a generator system are a prime mover driving an alternator, fuel tanks,operating controls and starter batteries. The generator has to be able to start automatically and toprovide the power for the load within 5 s (or in some cases within 15 s) as detailed in BS 5266-1.As with all central systems, the distribution wiring must be fire protected and also the last normallighting circuits must be monitored and the emergency luminaires automatically activated if thelocal circuit fails. As compliance with the safety requirements for the whole generator systemmay be arduous, it may be preferable to provide one-hour duration battery-powered luminairesin addition to the generator set. Testing of generators should be in accordance with themanufacturer’s instructions and Home Office guidance.

8.4.2 CircuitsCablingFor self contained systems, all the wiring is internal to the luminaire. The luminaire shouldconform to BS EN 60598 and be CE-marked.

For central systems, the integrity of the system is the paramount design consideration as thefailure of a single part could render the entire emergency lighting installation ineffective. Wherepossible, the power supply should incorporate some redundancy, for example more than onebattery room and multiple distribution circuits can be provided. To enhance integrity further, thedistribution circuits should be divided and segregated such that the risk of a total loss ofemergency lighting in any one area is minimised. Precautions should include the use of firesurvival cables such as mineral-insulated copper conductor (MICC) cables, armoured powercables to BS 7846 or low-smoke-and-fume (LSF) cables in protected routes. Examples ofmethods of protection include metal trunking and conduit. Cables run in ceiling voids that donot form part of a fire-rated zone should not be run in open trays unless they are of the MICCtype, armoured cable to BS 7846 or conform to cable performance standards BS 6387 or IEC60364-5-52. Particular attention should be paid to the most vulnerable parts of the distributionsystem, for example where cabling enters and leaves enclosures and luminaires. Suitable glandsshould be provided which maintain the same level of integrity as the cabling being used. Whereslave luminaires are spurred off a main circuit, the final cabling should be to the same standard asthe rest of the system. Cabling provided solely for emergency lighting purposes should be clearlyidentified as such and labelled accordingly. It is desirable to include some form of sensing toprove the integrity of the emergency lighting circuits.

Electromagnetic compatibility (EMC)It is also important that the overall design of a centrally supplied emergency lighting system isEMC compliant, as many of the components used in these systems, although individuallysuitable, may interact in such a way as to generate electrical interference. Verification should besought from the equipment manufacturers and systems integrators that EMC issues have beenconsidered properly This is particularly important when attempting to convert conventionalluminaires to emergency lighting luminaires with an ‘emergency pack.’


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gProtectionCabling, changeover relays and luminaires should be resistant to interference from transient over-voltages caused by supply surges and by switching (changeover). Protection should beprovided which ensures safe operation of the emergency lighting under transient conditions, as well as protecting the equipment itself from damage.

Surge-protection devices should be self-resetting and not render the emergency lightinginoperative.

InteractionsWhere a building management system (BMS) is employed, it is essential that any failure of thisdoes not adversely affect the emergency lighting, for example by incorrectly switching maintainedluminaires. A BMS failure should not be seen by the emergency lighting system hold-off relaysas a general lighting power supply failure.

Lighting controls may be in use on circuits that include emergency lights. The permanent linefeed to hold-off relays should be taken from a point that is independent of the control-systempower supply. Where dimming systems are linked to fire alarms (e.g. in restaurants and nightclubs), note that lighting provided by the dimming system under alarm conditions is additional to and separate from the emergency lighting.

Special circuitsIn addition to these general considerations, there are some special circuits required formaintenance work or testing. For details, see SLL Lighting Guide 12: Emergency lightingdesign guide.

8.4.3 LuminairesThere are two basic types of emergency lighting luminaires: self-contained and slave. Theseshould both conform to BS EN 60598-2-22.

Self contained luminairesSelf-contained emergency luminaires contain a battery to provide power and may be of threetypes: maintained, non-maintained or combined. A maintained luminaire is one in which all theemergency lighting lamps are operating when the normal lighting is on and when there is afailure of the mains electricity supply. A non-maintained luminaire is one in which all theemergency lighting lamps are in operation only when the electricity supply to the normal lightingfails. A combined (or sustained) luminaire is one containing at least two lamps, one of which isenergised from the normal lighting supply and the other from the emergency lighting supply.

Self-contained luminaires may be dedicated or may be converted from normal luminaires byadding an emergency conversion unit. If the work is not carried out by the original equipmentmanufacturer, the person who does it must have relevant training and experience. More detailedguidance can be found in ICEL Publication 1004. The product must be retested for compliance with CE-mark requirements and conform to BS EN 60598-2-22.

Slave luminairesSlave luminaires are normal luminaires that have mains-voltage operating components or havecomponents intended only for emergency use, and have a power feed from a central emergencypower source. Special care must be taken over the loop-in and loop-out of supply wiring using joint glands so that fire will not damage the feed cables in the luminaire.


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Alternatively, the luminaires may be fed by means of a spur off a protected ring. Slave luminairesmay be designed to operate from either AC or DC power supplies. For an AC supply, theluminaire is normally AC, but may be DC with internal rectifiers. Supply voltage in emergencymode may not be the same as that in mains mode — if the luminaires are maintained, achangeover relay will be needed. For a DC supply, the luminaires may be DC or fitted with aninverter to operate on AC. Again, if they are maintained, a changeover relay will be required. Inboth cases, the designer must be clear as to the lumen output available from the luminaires inemergency mode.

8.4.4 Luminaire classificationTable 8.2 shows an emergency lighting luminaire classification system. The resulting codeidentifies the type of system, mode of operation, facilities, and for self-contained luminaires, the rated duration. The classification of a specific emergency lighting luminaire is shown by thelabel attached.

Table 8.2 Emergency lighting luminaire classification

Type

X = Self-contained

Z = Central system

Facilities

A = Includes test device

B = Includes remote test module

C = Includes inhibiting mode

D = High-risk task luminaire

Duration for self-contained

luminaires

10 = 10 minutes

60 = 1 hour

120 = 2 hours

180 = 3 hours

Mode of operation

0 = Non-maintained

1 = Maintained

2 = Combined non-maintained

3 = Combined maintained

4 = Compound non-maintained

5 = Compound maintained

6 = Slave

8.4.5 Light sourcesTo be suitable for use in emergency lighting luminaires, light sources need to have fast run-upand restrike times, and preferably a long life. Tungsten and tungsten halogen lamps areinfrequently used because of their low efficiency and short life, except in low-temperatureapplications because in such conditions their light output is not affected.

The fluorescent lamp with hot cathodes, in either linear or compact form, is the lamp used formost emergency lighting applications because its high efficiency and long life are an idealcombination. However, cold-cathode lamps, despite lower efficiency, can be useful because oftheir even longer lamp life. Lamps with internal starters should not be used. Also, care must betaken when using amalgam versions of fluorescent lamps because these have slow run-upcharacteristics.


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gHigh-pressure discharge lamps are not normally suitable for emergency lighting because oftheir extended run-up and restrike times.

Light emitting diodes can be used, particularly for safety signs where long lamp life is a priority.They are also very efficient at low temperatures.

An important consideration in selection of lamps for use in emergency lighting is the likelihoodof lamp failure, as any dark spot in an emergency lighting installation can be dangerous.Information on the likelihood of lamp failure is given in the lamp survival factor (LSF). Table21.3 gives typical LSFs for a range of common lamps. For accurate results, the lampmanufacturer’s data should be used for all actual designs of emergency lighting. The data arebased on lamps running on conventional control gear and thus give values of survival factor thatmay be expected for maintained emergency lighting installations. LSF in non-maintainedinstallations is harder to predict. Although the number of hours that lamps are running in non-maintained installations is low, it is common for the control gear to heat the cathodes offluorescent lamps continuously by passing a current through them; regular inspection istherefore necessary to ensure all units are working.

8.4.6 OthersThere are two forms of safety sign that do not require any power to be delivered. One usesradioactive tritium as a light source. Tritium powered signs give a low light output but can beuseful in locations where flammable or explosive atmosphere is present. A risk assessmentshould be undertaken to ensure that their output is adequate at the location where they areintended to be used. Special care must be taken during disposal of these devices as they areradioactive; there are legal obligations for safe handling and storing.

The other uses the phenomenon of photoluminescence to provide light (see Section 3.1.4). Forthis to work, the sign has to be well illuminated prior to the emergency. In the event of mainsfailure, a chemical reaction, created by the previous illumination, causes the sign to emit light ata low level, considerably less than the signage requirements of BS 5266-7/BS EN 1838;however, they are useful to provide additional information and are required for emergencylighting on ships.

Low-mounted way guidance systems may be used in addition to the required emergencylighting. Such systems should conform to BS 5266-6.

8.5 Scheme planning

8.5.1 Risk assessmentThe first step in planning an emergency lighting installation is to carry out a fire riskassessment. In work places where five or more people are employed, such an assessment is alegal requirement. A fire risk assessment requires working through the following steps:

Identify potential fire hazards in the workplace: sources of ignition, fuels, work processes.

Identify the location of people at significant risk in case of fire: who might be in danger (employees, visitors) and why?

Evaluate the risks: are safety measures adequate or does more need to be done (fire detection, warning, means of fighting fire, means of escape, fire safety training of employees, maintenance and testing of fire precautions?)


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Carry out improvements.

Record findings and actions taken: prepare emergency plans, inform, instruct and train employees.

Keep assessment under review: revise it when situation changes.

8.5.2 Recommended systems for specific placesThe schedule in Table 8.3 is intended for guidance only. The recommendations assume that therisk assessment has been completed and that the space has no windows or has windows but thespace is in use after daylight hours, or that the daylight does not penetrate into the space. It isalso assumed that the occupants/visitors have adequate familiarity with the layout of theemergency routes and facilities of the building, that occupants of small rooms are able to vacatetheir rooms without emergency lighting but that corridors, stairs and escape routes are providedwith emergency lighting. It is essential that routes and exit doors are kept clear andunobstructed so that they are fit for use at all times. It is also important to avoid placingemergency lighting luminaires on escape routes or close to exit doors in such a position thatthey cause disability glare to those evacuating the building.

Most premises requiring emergency lighting can be associated with areas in the ‘generalbuilding areas’ section of Table 8.3. Other applications are included only if there is a change tothe ‘general building area’ recommendations. Note that some of the recommended durationsand modes of operation are subject to statutory requirements and should be determined duringconsultation with the appropriate enforcing authorities.


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gTable 8.3 Recommended systems for different building types. In this table, M = maintainedemergency lighting, NM = non-maintained emergency lighting, and the number following isthe minimum duration in hours.

Application (area)

General building areas

Entrance lobby/reception

Corridors

Staircase

Staff restaurants

Telecommunication/control rooms

Plant room/boiler room/liftmotor room

Lift

Toilet

Offices (cellular)

Offices (open plan)

Department store

Covered shopping complex

Non-domestic residential

Hotels/boarding houses

Hospitals

System

NM/1

NM/1

NM/1

NM/1

NM/3

NM/3

NM/1

NM/1

Notrequired

NM/1

NM/1

NM/1

NM/3

NM/3

Notes

Consider security

Consider identification of exits

Consider identification of exits

Consider additional requirements if used forentertainment purposes

Consider additional illuminance, e.g. 5 lx

Consider additional illuminance, e.g. 5 lx

Refer to BS 5655-1

Only required for toilets greater than 8 m2 floor area

(see BS 5266)

Consider emergency lighting where an office gives access to other areas or where large areas

of open plan are proposed

People may be unfamiliar with layout



Escape lighting required for themovement of patients and staff to

safe location. Longer durations may be necessary. Standby

lighting may be needed for thecontinued treatment of patients

Locations of luminaires

Wall or ceiling mounted

Wall mounted at changes of direction orlevel, at fire alarm call points and at

firefighting equipment

Wall or ceiling mounted at each landing

Wall or ceiling

Wall or ceiling to illuminate switchboard, control desk etc

Wall or ceiling to illuminate panels, plant switchgear etc

Ceiling

Wall or ceiling

Exit signs on wall or ceiling

Ceiling

Wall or ceiling

Wall or ceiling (shatter proof)

Ceiling or wall (see general building areas)Special care required in identifying meansof escape with directional and exit signs

Ceiling or wall


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Application (area)

Public places

Cinemas (auditoria)

Theatres (auditoria)

Places of assembly

Covered car parks

Computer rooms

Conference facilities

Industrial factories

Educational andrecreational

Schools, colleges

Sports

Pedestrian walkways,where forming part of

the escape route

Museums and art galleries

System

M/3

M/3

NM/1

NM/1

NM/1

NM/1

NM/1

NM/1

NM/1

NM/1 orNM/3 onlarger sites

Notes

Lower illuminance of 0.02 lx isgenerally maintained during

public use

As above but illuminance raised to 0.2 lx when normal supply fails

Other systems may be acceptabledepending on size and location

In some cases, exit signs may be adequate

Where standby or no-break supply is available emergency lighting may

be connected to this supply

Consider unfamiliar persons usingfacilities. Consider alternative

applications of facilities

Consider additional luminaires to highlight specific hazards

Consider additionalluminaires for entertainment use

out of normal hours. Consideralternative applications of area

Consider alternative applications of area and the mechanical protection of equipment

Consider waterproof luminaires ifwalkways are exposed or external

Consider security aspects

Locations of luminaires

Ceiling or wall. Special care required in identifying means of escape with

directional and exit signs

Ceiling or wall. Special care required in identifying means of escape with


Ceiling. Shatter-proof luminairesshould be considered. Special carerequired in identifying means of

escape with directional and exit signs

Ceiling or wall to illuminate working areas and walkways

Ceiling or wall and exit signs

Locate to define gangways, corridorsand safe areas. Proof luminaires may

be required in some areas (IP54)

Ceiling or wall

Wall or ceiling, shatterproof. Specialconsideration of location

Wall. Shatterproof luminaires should be considered

Wall or ceiling. Special care required in identifying means of escape with



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8.5.3 Planning sequenceGiven that the risk assessment reveals a need for emergency lighting, it is then necessary toidentify the lighting requirements that have to be met, the type of system to be used and itsmode of operation. Once these decisions have been made, the next step is to adapt the genericdesign to the specific location. Advice on how to do this can be found in SLL Lighting Guide12: Emergency lighting design guide.

8.6 Installation, testing and maintenance

The success of an emergency lighting system depends not only on the design, planning andselection of the right equipment but also on the satisfactory installation and maintenance of theequipment throughout its service life.

8.6.1 InstallationThe emergency lighting system should be installed as instructed by the designer of the schemeand in accordance with the equipment manufacturer’s instructions. The designer usuallyprovides a schedule of installation, including scheme plans and wiring/piping drawings in whichthe location of equipment, placing of protection devices and the choice and routing ofwiring/piping are set out. The schedule or drawings may also give the sequence of fixing andconnections, particularly of complex systems. All such schedules and drawings should be addedto the logbook on completion of the installation. These should be updated with information ofall scheme modifications made during the life of the installation.

8.6.2 Maintenance and inspectionMaintenance and inspection of the installation should be done regularly. The designer shouldprovide a maintenance schedule that should list and give details of replacement componentssuch as lamp type, battery, fuses, cleaning and topping-up fluids.

Caution should be exercised while carrying out maintenance as un-energised circuits maysuddenly become energised automatically. Prime movers and generators will almost always bestarted without warning in an emergency or automatic test since a sensor remote from the plantenclosure initiates the sequence of operations.

Batteries should be maintained in accordance with the manufacturer’s recommendations.Sealed batteries used in self contained luminaires require no maintenance. Self-containednickel–cadmium (Ni–Cd) batteries have an operational life of four years. After this period thebatteries must be replaced with a type specified by the manufacturer. Sealed batteries, used incentral systems, will not require maintenance but it is advisable to check, clean and grease theterminals at regular intervals.

Luminaires and safety signs should be cleaned at regular intervals that may coincide with thetime of inspection. Any defects noted should be recorded in a logbook and rectified as soon aspossible. The cleaning interval is dependent on the environment around the installation.Serviceable components should be replaced at the end of the recommended component servicelife by an approved part.

Inspection and testing of various aspects of emergency lighting should be carried out daily,monthly and yearly.

The charging supply to central battery systems should be checked daily as should progress onrectifying any faults entered in the logbook.


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A short-duration test should be performed monthly, by simulating a failure of the normallighting power supply, to verify that all emergency luminaires are operating. This applies forboth self-contained and central systems. The duration of the function test should be as brief aspossible, so as not to discharge batteries unduly or damage the lamps. Generators should bechecked for automatic starting and to ensure that they energise the emergency lighting system correctly.

A full duration test of all systems should be performed yearly, to verify that the emergencylighting provides its design output for the full design duration. The duration test should bearranged to occur when the time needed to recharge batteries has the least impact on theoccupation of the building.

Records should be kept of all the tests made and of the results obtained. Where self-testing orremote testing features are being used, those responsible for emergency lighting systems shouldverify that the tests have been conducted on schedule and have given satisfactory results. Detailsof routine testing are given in BS EN 50172: 2004.

An increasing trend is for emergency lighting to incorporate some form of self-testing facility,or for the luminaires to incorporate a remote monitoring feature. The electrical test shouldverify that any self-testing system performs as intended, without impairing the integrity of thelighting design. Where self-testing or remote monitoring systems are used as the basis ofcompliance with BS 5266-1: Section 12, visual inspection of the installed equipment should becarried out at least annually to verify that it is in good mechanical condition. BS EN 62034:2006 gives details of automatic test systems for battery powered emergency escape lighting.

8.6.3 DocumentationGiven the extensive regulatory framework associated with emergency lighting, gooddocumentation of the installation is essential. The documentation should include thecompletion certificate, an initial inspection certificate based on the model in BS 5266-1,a maintenance schedule and a logbook.

8.6.4 Commissioning and certificationElectrical testingA full electrical test in accordance with BS 7671 is required when commissioning an emergencylighting installation.

For self-contained systems, an electrical test should be carried out to ascertain that allluminaires are working in the correct manner, i.e. maintained, non-maintained and, whereappropriate, combined. It should be verified that the battery-charging supply is present andindicated, and that the luminaires operate in emergency mode on simulation of a general supplyfailure. After initial commissioning, and allowing for a full charge of all batteries, it is goodpractice to perform a duration test to confirm that the system will perform for the designedduration. It should be confirmed that all luminaires reset to normal or standby mode asappropriate after the restoration of the normal supply. Where additional controls such asswitched–maintained, inhibiting or rest mode are fitted, it shall be verified that these operate inthe correct manner.

For central battery or generator systems, the system should be tested in normal and emergencymodes to determine the correct changeover of luminaires and full functionality in emergencymode. With central systems, it is essential that a duration test is carried out.


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gIt should be confirmed that all luminaires and off-line battery units reset to normal or standbymode, as appropriate, after the restoration of the normal supply.

Where self-testing and remote testing systems are included, the system should be set up andtested for functioning in accordance with the suppliers’ instructions. A copy of theseinstructions should be placed with the logbook.

Photometric testingPhotometric measurements to confirm that the system meets the lighting requirements are alsodesirable. When photometric measurements are being made, it is necessary to ensure that thecorrect power-supply voltages are present. On-site performance testing of emergency lightinginstallations can be very difficult. The testing requires good instrumentation and well laid outplans for the measurement conditions.

Any illuminance meter used should have a photocell with good cosine incident light correction.An illuminated-dial or digital-display type meter should be used so that readings may be visibleat low illuminances. The light meter should have an operating range of 0.001 to 10.0 lx with asensitivity of 0.001 lx for escape routes and areas, and a range of 10.0 to 1000.0 lx with asensitivity of 1.0 lx for high risk areas. The accuracy of the instrument should conform to BS 667 Type F. The photocell should preferably be on a remote lead to avoid shadowing.

The illuminance measurements should be made on a horizontal plane on the escape route areaor task area. In most cases it is advisable to select a number of specific areas or points for testthat represent the worst conditions. See SLL Lighting Guide 12: Emergency lighting design guidefor suggested measurement locations.

The results of these illuminance measurements can be checked against design data.Measurements should be taken during the hours of darkness. If there is steady extraneous lightfrom street lighting or moonlight the contribution of the emergency lighting can be estimatedby taking the difference between measurements of the same point, with and without emergency lighting.

The illuminances provided by the emergency lighting system will vary with time, so the testsshould be completed as quickly as is possible within the rated duration. This will minimise thecharge losses from the batteries. This is particularly relevant in an occupied building because,with fully discharged batteries, the building may have reduced emergency lighting cover for upto 24 hours. It is valuable to have data that relate the lumen output of the luminaire at any timeto the lamp/battery life cycle.

8.6.5 Completion certificateOn completion of design, installation and commissioning of the emergency lighting system, acompletion certificate should be prepared and supplied to the occupier/owner of the premisesas part of the handover. An example of a completion certificate is given in SLL Lighting Guide12: Emergency lighting design guide. All sections of the completion certificate should be signed bythe specified competent persons.


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Chapter 9: Office lighting

9.1 Functions of lighting in offices

As the UK has moved from a manufacturing economy to a service economy, the number ofpeople working in offices has increased. The purpose of office work is the collection, recordingand distribution of information, together with the making of decisions based on thatinformation and the direction of effort to carry out the decisions made. What has changed inoffices over the last twenty years has been immense growth in the ability to collect, record anddistribute information rapidly, over vast distances, electronically. This process began with theintroduction of the personal computer, gained strength with the development of local networksand reached its full flowering with the arrival of e-mail and the World Wide Web.

The function of lighting in offices is primarily to make the information handled visible, withoutdiscomfort. Consequently, the change from paper-based work to screen-based work hasimportant implications for lighting. In the paper-based office, the primary surface to be viewedis horizontal and increasing the amount of light makes any information on that surface morevisible. In the computer-based office, the primary surface to be viewed is vertical and increasingthe amount of light in the office makes the information displayed on the self-luminous screenless visible. But this distinction is more theoretical than actual, a survey of offices today wouldreveal very few that were completely screen-based or completely paper-based. The vast majorityof offices use a combination of paper and screen. This means that any lighting installationdesigned for an office today has to be satisfactory for materials that are self-luminous, i.e.computer screens, and seen by reflected light, i.e. paper, and for lines of sight that can be bothacross the office and down at the desk.

9.2 Factors to be considered

Offices come in many different forms. They can be private or multi-occupied. If multi-occupied they can be open-plan or furnished with cubicles. They can have varying amounts ofdaylight available. They can fill complete buildings or be part of other buildings. Despite thevariability faced by the designer of office lighting, the objectives are the same everywhere. They are:

to facilitate quick and accurate work

to contribute to the safety of those doing the work

to create a comfortable visual environment.

To meet these objectives it is necessary to consider many aspects of the situation.

9.2.1 Legislation and guidanceThere are several different pieces of legislation relevant to office lighting, ranging fromstatements of general principle to specific requirements.

Under the Health and Safety at Work Act 1974 the employer must, as far as reasonablypracticable, provide and maintain a safe working environment with adequate lighting.

In Section 8 of the Offices, Shops and Railway Premises Act 1963, reference is made to suitableand sufficient lighting, either natural or artificial.


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Most associated Regulations and Acts call for adequate lighting and installation maintenance,some of these are listed below:

Health and Safety (Signs and Signals) Regulations 1996, (plus BS 5266, EN 1838)

Building Regulations, Part L: Conservation of fuel and power

Building Regulations, Part B: Fire safety

Fire Precautions (Workplace) Regulations 1997

Visual Display Screens Act 1992

Electricity at Work Regulations 1989.

Extensive guidance on office lighting is given in the SLL Lighting Guide 7: Office lighting.

9.2.2 Type of work doneThe stereotypical office consists of a room filled with workstations or desks where individualshandle information presented either on paper or on a screen. While this is undoubtedly part of the work done in an office, frequently office work requires verbal communication betweenindividuals. This can be done by telephone, via a video link or face to face. That this is so isevident from the existence of meeting rooms, conference rooms, boardrooms and trainingrooms in many offices. The lighting of such spaces should be designed to facilitate non-verbalcommunication as well as the visibility of paper and screen-based materials. Offices also containcirculation and reception areas, such areas frequently representing the public face of the business. The lighting of such areas should be designed to send the required message to the visitor.

9.2.3 Screen typeAn important consideration for office lighting is the optical and geometric properties of thecomputer screens in the office. The relevant optical properties are diffuse reflectance, specularreflectance, display polarity and display background luminance. The relevant geometricproperties are screen tilt and curvature.

The optical properties of the screen matter because they determine the visibility of reflectionsfrom the screen relative to the visibility of the display itself. The higher the diffuse reflectance,the greater will be the reduction in contrast of the display. The higher the specular reflectance;the sharper will be the reflected image in the screen and the greater the probability that it willbe distracting. A positive polarity screen (bright characters on a dark background) will makereflected images more visible than a negative polarity (dark characters on a bright background)screen. The higher the background luminance of the display, the less visible will be thereflected image in the screen. What all this means is that a computer screen with anti-reflectiontreatment and a negative contrast display with a high background luminance, has a lowprobability of disturbing screen reflections. Conversely, a screen without anti-reflectiontreatment, using a positive contrast display with a low background luminance will be verysensitive to the lighting conditions.


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Given that the optical properties of the screen are such that reflections are likely to be seen, thenthe geometry of the screen becomes important because it determines the probability that highluminances, such as those produced by luminaires, will be in a position to cause disturbingreflections in the screen. Office lighting installations are almost always installed in or on theceiling, so the further the screen is tilted from the vertical the more likely it is that disturbingreflections will occur. As for screen curvature, the more curved the screen, the larger the area ofthe office that is reflected in the screen.

Wherever possible, it is desirable to know the optical and geometric properties of the screens thatwill be used in the office because different properties place different constraints on the design ofthe office lighting (see Section 9.3.3 Maximum luminances).

9.2.4 Daylight availabilityMost offices have access to daylight through windows. Depending on the time of day and seasonof the year, the weather conditions, the size and shape of the windows, the orientation of thewindows and the presence of external obstructions, the amount of daylight available in the officecan vary over a wide range. It will always be necessary to install electric lighting for use after darkbut whether or not to invest in a control system that automatically adjusts the electric lighting tosupplement the available daylight will depend on the amount of daylight available. As a crudeguide, in offices where the minimum daylight factor is less then 2 percent there is little to begained from modifying the electric lighting. Where the minimum daylight factor is more than 5percent, controlling the electric lighting to blend with daylight should always be considered.

Of course, daylight will only be available if the window is unobstructed and a short walk aroundany business district will show how frequently windows are obstructed. Windows may beobstructed for a number of reasons. Among them are visual discomfort caused by a direct view ofthe sun or bright sky; visual discomfort caused by the presence of high luminance patches ofsunlight on the workstation; visual discomfort caused by reflected images of the windows incomputer screens; and thermal discomfort caused by excessive radiant heating or cooling. Visualdiscomfort can be minimised by careful attention to external shading of the windows or the useof different types of glazing or internal screening (see SLL Lighting Guide 7: Office lighting). Theproblem of reflections from computer screens can be solved by orienting the screens so that theyare perpendicular to the plane of the windows. As for thermal problems, these have to be dealtwith through the heating and ventilating system.

9.2.5 Ceiling heightCeiling height is important for office lighting design because it determines whether indirectlighting is an option. Floor, furniture and wall mounted indirect lighting luminaires rely onheight to shield the occupants of the office from a direct view of the lamp. This is the reason why the vast majority of floor mounted luminaires are at least 1.8 m high and why wall and furniture mounted indirect luminaires should have their top surface at least 1.8 m above the floor.

This minimum height above the floor for luminaires sets a minimum ceiling height that can be used for indirect lighting. As a rule of thumb, floor furniture and wall mounted indirectlighting luminaires are best used with ceiling heights in the range 2.5 m to 3.5 m. Below 2.5 mthere is a risk of high luminance ‘hot spots’ being produced on the ceiling. Above 3.5 m theadditional energy consumption required for floor mounted indirect lighting becomes difficult to justify.


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Where indirect luminaires are suspended from the ceiling, the luminaires need to be well above normal head height. A minimum height of 2.3 m to the underside of the luminaire isrecommended. As for the separation from the ceiling, this is a matter of luminaire design.Manufacturers usually specify a minimum separation from the ceiling. This minimum should not be ignored.

9.2.6 ObstructionObstructions in offices are created by the use of partitions between individual workstationsand/or the use of full height partitions to subdivide the office.

The degree of obstruction created by the use of partitions between individual workstations willdepend on the height of the partitions; the higher the partition, the greater the obstruction. 1.2 m high partitions provide visual privacy for anyone sitting at the workstation but not whenstanding. 2 m high partitions provide visual privacy for both sitting and standing occupants. Anoffice equipped with 2 m high partitions is effectively a collection of very small offices. This hasboth advantages and disadvantages for lighting. The advantage is that luminaires and windowsare very unlikely to be seen reflected in the computer screen. The disadvantage is that theamount of light on the workstation will be reduced unless allowance is made for the additionallight absorption in the design of the electric lighting. As for daylight, the presence of partitionsbetween workstations limits the role of windows in providing a view out, the amount ofdaylight reaching the workstation being negligible.

Figure 9.1A view of partitioned office

Most office buildings constructed for lease show the office floor as one large open space butrequire the lighting to be designed so as to allow full height partitions to be installed tosubdivide the space into offices of different sizes. The effect of these partitions will depend onthe size of the offices created and the reflectance of the partitions. The smaller the office andthe lower the reflectance of the partitions, the greater is the reduction in illuminance. Ideallythe designer needs to know the size of the smallest office in order to determine the mostsuitable type and layout of lighting. Thought will also have to be given to the control system forthe lighting.

9.2.7 Surface finishesThe colour and reflectance of all the surfaces in an office influence the distribution of light.Figure 9.2 gives recommended ranges of average cavity reflectances for floor and ceiling and theaverage wall reflectance.


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Figure 9.2Recommended ranges of floor and ceiling cavity reflectance, wall reflectance and relativesurface illuminance in offices

When estimating the average surface or cavity reflectance it is necessary to take into account allthe reflectances forming the surface or cavity. For example, if a painted wall is lined with filingcabinets, the average wall reflectance is made up of the reflectances of the painted surface andthe filing cabinets weighted by the area of each. Table 9.1 gives the reflectances of somecommon materials found in buildings and some paint colours. Details of the reflectance ofother materials can often be obtained from the manufacturers or by the methods described inSLL Lighting Guide 11: Surface reflectance and colour.

For direct lighting, where the luminaires are recessed into the ceiling, light reaching the ceilingand upper part of the walls is first reflected from the floor and work stations. To avoid a gloomyappearance caused by dark walls and ceiling it is necessary to have a floor cavity reflectancetowards the top end of the range given in Figure 9.2. Unfortunately, it is difficult to achieve thiswithout using a light floor finish, something that is not practical in heavily trafficked offices.The solution to this problem is a supplementary lighting installation designed to light theceiling directly.

There are also limitations on the colour of the floor finish. Where direct lighting withluminaires recessed into the ceiling is used, the ceiling is illuminated primarily by light reflectedfrom the floor. Consequently, a strongly coloured floor will result in a strongly coloured ceiling.

Task illuminance1.0

Effective wallreflectance 0.3 to 0.7

Relative wallilluminance0.5 to 0.6

Effective floor cavityreflectance - 0.2 to 0.4

Window wallreflectance - 0.6minimum

Ceiling cavity reflectance 0.6 minimumRelative ceiling illuminance 0.3 to 0.9


Materials

White paper

Stainless steel

Cement screed

Light carpet

Light oak veneer

Teak veneer

Dark oak veneer

Quarry tiles

Window glass

Dark carpet

Reflectance

0.85

0.81

0.68

0.64

0.45

0.22

0.18

0.15

0.14

0.10

0.10

0.05

Reflectance

0.8

0.4

0.4

0.3

0.4

0.2

0.1

0.1

0.1

0.1

Paint colours and BS 4800 code

White 00E55

Pale cream 10C31

Light grey 00A01

Strong yellow 10E53

Mid grey 00A05

Strong green 14E53

Strong red 04E53

Strong blue 18E53

Dark grey 10A11

Dark brown 08C39

Dark red-purple 02C39

Black 00E53

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There is much to be said for the use of high reflectance surface finishes of neutral or low chromacolour, particularly in small offices. Surface finishes of this type increase the inter-reflectedcomponent of the illumination thereby diminishing shadows and reducing the probability that the occupants will experience discomfort glare or be annoyed by veiling reflections.

For indirect lighting (see Section 9.4), it is important to provide a high ceiling cavity reflectancefree from colour. Failure to do this will result in an inefficient installation producing colouredlight. It is also desirable to use large areas of high reflectance on the walls to enhance the inter-reflected component of the illumination, with small areas of colour to offset the blandness ofindirect lighting.

For direct/indirect lighting (see Section 9.4), a high ceiling cavity reflectance free from colour is again desirable to ensure the efficiency of the indirect lighting. However, there is no need tohave a high floor cavity reflectance as the ceiling is illuminated by the indirect lighting.

For general guidance, Table 9.2 recommends the range of reflectances for the most commonsurfaces in an office.

Table 9.1 Reflectances of common materials found in buildings and some paint colours

Surface

Ceiling

Walls

Partitions

Floor

Furniture

Window blinds

Reflectance

> 0.7

0.5–0.7

0.4–0.7

0.1–0.3

0.2–0.5

0.4–0.6

Table 9.2Recommended reflectance ranges forcommon office surfaces


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Floor reflectance

0.1

0.2

0.3

Minimum cylindrical/horizontal illuminance ratio

0.48

0.37

0.26

Space

Open plan office – mainly screen based work

Open plan office – mainly paper based work

Deep plan core area (more than 6m from window)

Cellular office – mainly screen based work

Cellular office – mainly paper based work

Graphics work stations

Dealing rooms

Executive offices

Recommended maintained illuminance

300 lx

500 lx

500 lx

300 lx

500 lx

300 lx

300–500 lx

300–500 lx

9.3 Lighting recommendations

9.3.1 IlluminancesOffices contain rooms with different functions. Tables 9.3 to 9.5 give the recommendedmaintained illuminances for the most common spaces in an office building. The recommendedmaintained illuminance is the minimum average illuminance that should be provided in thegiven space throughout the life of the installation. Unless specified otherwise, the recommendedmaintained illuminance is measured on a horizontal working plane at desk height. Table 9.3 givesthe recommended maintained illuminances for the primary office spaces. A primary office spaceis a space where most of the work is done and where most of the staff spend most of their time.

Table 9.3 Recommended maintained illuminances on a horizontal working plane in primaryoffice spaces.

These maintained illuminances are adequate for task performance but are insufficient to ensurecomfortable visual conditions, particularly for deep offices with windows and large open planoffices. For deep offices with windows, there is a risk that the parts of the office away from thewindows will look dull compared with the parts adjacent to the windows. This perception can beovercome by taking care to light the walls of the office as well as the horizontal plane. For largeopen plan offices, lighting the walls is still useful but will not be effective in the centre of theoffice where there are no walls. In such areas, an additional illuminance criterion should beapplied. This is the ratio of cylindrical illuminance to horizontal illuminance at a height of 1.2 mabove the floor. Table 9.4 gives the minimum values of this ratio recommended for different floor reflectances.

Table 9.4 The minimum cylindrical/horizontal illuminance ratios recommended for differentfloor reflectances


Recommended maintained illuminance for special situations

500 lx (if more intense reading and writing is done)




300 lx (on collating, binding and dispatch tables)

200 lx (vertically on bookcases); 500 lx (on reading desks and counters)

200 lx (vertically on fronts of shelving)

300 lx (on serving and preparation areas)

500 lx (on medical examination area)

300 lx (serveries); 500 lx (kitchens)


300 lx (for normal meetings)




300 lx (vertical onreprographic equipment)

300 lx (general)

300 lx (general)

200 lx (general)

300 lx (general)

200 lx (general)

Space

Meeting or break-out rooms

Training rooms

Conference rooms

Board rooms

Reprographics rooms

Libraries/informationcentres

Archives/documentstores

Break rooms

Medical rooms

Canteens/restaurants

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For a regular array of luminaires, the cylindrical/horizontal illuminance ratio should becalculated or measured at two positions, one directly beneath a luminaire and the other at themidpoint between luminaires. The minimum cylindrical/horizontal illuminance ratio should beexceeded at both positions.

Offices frequently contain a number of secondary spaces that are used intermittently for a widevariety of purposes. Table 9.5 gives the recommended maintained horizontal illuminances forthese secondary spaces. Where face to face interaction is important it will also be necessary toprovide adequate vertical illuminance. These spaces can contain specialised equipment orfurnishings that require lighting to different illuminances than the general lighting (see SLLLighting Guide 7 for advice).

Table 9.5 Recommended maintained illuminances for secondary office spaces

All offices have circulation areas and service areas. Table 9.6 gives the recommendedmaintained illuminances for these areas, some of which will contain special equipment thatrequires lighting to different illuminances than the general lighting in the space.


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Recommended maintained illuminance for special situations

300 lx over reception desks andseating areas

300 lx where there is use of written materials

200 lx vertically on control panels,valve sets and instruments etc

300 lx vertically on machines, 500 lx on workbenches

200 lx vertically on sides ofwinding machine and front of

control panel

200 lx vertically on sides ofgenerator, front of control panel

and instruments etc

200 lx vertically on front of shelving


200 lx (general)

150 lx (on treads)

200 lx (on floor)

100 lx (on floor)

200 lx (general aroundCCTV monitors)

200 lx (general)

200 lx (general)

300 lx (general)

200 lx (general)

200 lx (general)

200 lx (general)

300 lx (general)

Space

Entrance halls/reception

Stairs/escalators

Lift lobbies

Corridors

Security/controlrooms

Cleaner’scupboards

Plant room

Workshops

Lift motor rooms

Generator/UPSrooms

Storeroom for bulk items

Storeroom for small items

Table 9.6 Recommended maintained illuminance for circulation and service areas

9.3.2 Light distributionThe illuminances given above are averages. To avoid complaints about non-uniform lighting, itis necessary to have limits on how much the illuminance on any single work surface is allowedto drop below the average. For any individual work surface, e.g. a desk, the illuminanceuniformity (the ratio of the minimum illuminance/average illuminance) should not be less than 0.7.

Most offices are furnished with many desks or workstations. To ensure different desks orworkstations are perceived to be treated equally, the illuminance uniformity (minimum averageilluminance on the desks/overall average illuminance) should not be less than 0.7. Thisilluminance diversity criterion applies to electric lighting designed to produce a uniformilluminance across the whole working plane. Where there is daylighting from side windows, orwhere individual control of the light output from luminaires is used, the illuminanceuniformity criterion should be ignored.


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The appearance of the office will also be affected by the illuminance of the walls and ceiling aswell as the working plane. Figure 9.2 shows desirable ranges of illuminance on the walls andceiling as a percentage of the average working plane illuminance. What illuminances are actuallyachieved on the walls and ceilings will depend on the type of office lighting used. For directlighting, the ceiling illuminance will be at the bottom end of the specified range. If this cannotbe achieved, some form of supplementary lighting to brighten up the ceiling is required. Forindirect lighting, it will not be possible to achieve a ceiling illuminance within the rangespecified, unless the illuminance on the working plane is increased through supplementarylighting. For direct/indirect lighting it should always be possible to achieve wall and ceilingilluminance percentages within the ranges specified.

9.3.3 Maximum luminancesOne of the concerns of people working in offices is the reflection of high luminance objects incomputer screens. Such reflections can be disturbing because they mask the display or distractattention from it. This used to be a major problem when screens used bright characters on adark background and were highly reflective but the development of better quality, higherluminance screens that allow dark characters on a bright background, and the wider use ofscreen treatments to reduce both diffuse and specular reflections made it less of a problem.Nonetheless, there are still many of the older type of screens in use and some of the newscreens designed to provide a crisp image are very specular so it is necessary to recognise thatlighting needs to be designed with care if problems are to be avoided.

The obvious solution to reflections from screens is to obtain a better quality screen. However, ifit is necessary to solve a screen reflection problem by doing something about the lighting thenthe answer is not to exceed the maximum luminance limits set for luminaires. Table 9.7 givesthe maximum luminances of any part of a luminaire that can be seen in a screen, for differentscreen types. The luminance limit is normally applied at and above a 65° angle of elevationwhere the screens are not tilted back more than 15°. Where screens are unusually sensitive toreflections, it may be necessary to use a 55° luminaire luminance limit angle.

Figure 9.3 Defining what can be seen reflected in a display screen

Windows

LuminaireCeiling

Tilt ofscreen

Curvature oftop of screen

Limit of area seenreflected in screen


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Screen type

Type 1: Good or moderatescreen treatment

Type 2: No screentreatment

Maximum luminaireluminance (cd/m2) where

some negative polaritydisplays are used

1000

200

Maximum luminaireluminance (cd/m2) where

only positive polaritydisplays are used

1500

500

9.3.4 Discomfort glare controlDiscomfort glare is controlled by ensuring that the unified glare rating (UGR) of the lightinginstallation does not exceed the maximum recommended value. Table 9.8 gives the maximumUGR values for different parts of an office. It is important to appreciate that differences inUGR of less than one unit are not meaningful.

Discomfort can also be caused by a view of the sun or bright sky through a window. Thissource of discomfort can be limited either by the use of light shelves and similar elements ofthe building structure or by blinds. The best blinds are those that shield the occupants from theexcessive brightness while preserving some of the view out.

Limiting luminaire luminance is important to solving a problem of screen reflections becauseluminaires are often the highest luminance object in the office, but not always. Sometimes, theview out of the window will have a higher luminance and, with indirect and direct/indirectlighting, the ceiling may have the highest luminance. For indirect lighting, it is recommended thatthe average luminance of the major surface reflecting light, which is usually the ceiling, should beless than 500 cd/m2 and the maximum luminance at any point should be less than 1,500 cd/m2.Further, the luminance variation across the surface should change gradually and not suddenly. The same criteria can be applied to windows, which will usually mean fitting some form of blind.

Table 9.7 Maximum luminaire luminance limit for different types of computer screen


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Category of space

Primary office space

Secondary office space

Circulation areas

Service areas

Type of office

Open plan offices

Deep plan areas

Cellular offices

Graphics work stations

Dealing rooms

Executive offices

Meeting rooms

Training rooms

Conference rooms

Board rooms

Reprographics rooms

Libraries/information centres

Archives/document stores

Tea points/rest rooms

Sick bays/medical rooms

Canteens/restaurants

Entrance halls/reception

Atria

Stairs escalators

Lift lobbies

Corridors

Security/building control rooms

Cleaner’s cupboards

Plant rooms

Workshops

Lift motor rooms

Generator/UPS rooms

Storerooms

Maximum UGR

19

19

19

19

19

19

19

19

19

19

22

19

25

22

19 (16 toward practitioner formedical examination)

22

22

-

25

22

25

22

25

25

22 or 19 depending on task

25

25

25

Table 9.8 Maximum UGR values for different parts of an office

9.3.5 Light source colour propertiesLight sources with a CIE general colour rendering index (CRI) of at least 80 should be used inall parts of the office, except the service areas. For service areas, light sources with a CRI of atleast 60 are acceptable.

As for colour appearance, the correlated colour temperatures (CCT) of light sources commonlyused in offices varies from 3,000 K to 5,000 K and sometimes as high as 6,500 K. The choicebetween these different CCTs is a matter of individual preference. CCTs at the lower end ofthis range will give a warm appearance to the interior but do not blend well with daylight.Higher CCTs will blend better with daylight but give a cool colour appearance to the space.


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Figure 9.4Direct lightingin an office

The main potential problem with direct lighting is the fact that the ceiling and the upper partsof the walls tend to be underlit resulting in a gloomy, cave-like appearance. This problem canbe alleviated in a number of ways. One is by using high reflectance finishes to the floor,furnishing, walls and ceilings. If this is not practical, then supplementary wall mounteduplighting can be used or a direct lighting luminaire can be chosen that diverts a small amountof light onto the ceiling (Figure 9.5). This will have the effect of making the office appearbrighter and more interesting although care has to be taken to avoid high luminance patchesappearing on the walls or ceiling as these may be seen as high luminance reflections incomputer screens.

Very high CCTs will also produce a perception of greater brightness for the same luminance and enhance visual acuity. Whatever light source CCT is chosen should be used throughout the office.

9.4 Approaches to office lighting

9.4.1 Direct lightingDirect lighting uses luminaires that are designed to emit the vast majority of their light outputdirectly down onto the nominal horizontal working plane. Any upward light emitted plays aninsignificant part in lighting the task. Direct lighting luminaires can be surface mounted,recessed into the ceiling or suspended (Figure 9.4).

Figure 9.5Reflectors suspended belowa direct luminaire to reflectsome light onto the ceiling


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Undesirable high luminance reflections of the luminaires can be eliminated by choosingluminaires within the luminance limits specified in Table 9.7. The same luminance limits willminimise discomfort glare to occupants looking across the office. To eliminate overhead glare it is necessary to shield any direct view of high luminance light sources such as T5 fluorescents, or clear envelope metal halides. In addition, it is better not to use highly specular reflectors with such high luminance light sources as these reflectors can provide an image of the lightsource with almost the same luminance as the light source itself.

For comparable illuminance distributions on a horizontal working plane, direct lighting willalmost always be more energy efficient than either indirect or direct/indirect lighting. However,the effectiveness of direct lighting may be compromised where there is a lot of obstruction frompartitions in the space. It is also important to appreciate that surface mounted or suspendedluminaires may interfere with air distribution in the office, thereby causing thermal discomfort.Coordination of luminaire layout and air distribution pattern is very desirable.

9.4.2 Indirect lightingIndirect lighting uses luminaires where all, or almost all, of the light produced by the luminaire isreflected off some surface, usually the ceiling, before reaching the working plane. In the interestsof energy efficiency it is important to ensure that the surface from which the light is reflected hasa high diffuse reflectance, at least 0.7 and preferably 0.8 and higher. In the interests of colourrendering, it is important that the reflecting surface is spectrally neutral in colour. The lightingeffect produced by indirect lighting is typically diffuse, without strong modelling or shadows.Therefore, it is important to use the office décor to provide some visual interest and variety. Thiscan take the form of small areas of strong colour associated with architectural features or gentlespotlighting of interesting features such as artwork or notice boards.

Figure 9.6Indirect lighting in an office

Indirect lighting can be highly effective in a heavily obstructed office. Further, provided themaximum surface luminances given in Section 9.3.3 are not exceeded, there should be noproblem with either discomfort glare to the occupants or high luminance reflection from screens.

Indirect lighting is most suitable for ceiling heights within the range 2.5 to 3.5 m. Indirectluminaires can only be used at ceiling heights in the range 2.3 to 2.5 m if careful attention is paidto light distribution to avoid high luminance spots occurring immediately above the luminaire.Ceiling heights greater than 3.5 m can be used but at extra cost in terms of installed power.Indirect lighting luminaires will usually be seen against the ceiling. To avoid excessive contrast,the outer surfaces of indirect luminaires should be light in colour.


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Figure 9.7Direct/indirect lighting in an office

Occasionally, ceiling recessed luminaires in which the vast majority of the light from the lightsource is reflected from the interior of the luminaire before exiting the luminaire are described as indirect luminaires. This is misleading. Such luminaires should be treated as direct lighting luminaires.

9.4.3 Direct/indirect lightingDirect/indirect lighting uses a luminaire or a combination of luminaires that provides somelighting on the working plane directly and some after reflection from a surface, usually the ceiling.Direct/indirect lighting can be very effective because the two components are complementary. By using direct/indirect lighting the office will have not only well-lit walls and ceiling but alsosome modelling (Figure 9.7).

The exact proportion of direct and indirect lighting is not critical in most circumstances althoughthe appearance of the office will change with a change in proportions. As a rule of thumb, if thelighting is to be considered direct/indirect lighting, the minimum percentage for either componentis 20 percent. The recommendations and limitations given above for direct lighting and indirectlighting should be applied to each component separately.

Direct/indirect lighting luminaires come in several different forms. One form uses the same lightsource or sources to provide the two components. Another uses different light sources for the two components. In this case, an option is often available to switch or dim the twocomponents independently. This option may be used to allow occupants to adjust the directlighting in their local area to match their own preferences but the extent of interaction betweenadjacent areas needs to be considered. Some direct/indirect lighting luminaires come with acanopy attached to provide a close-up reflector for the indirect component. This is useful in spaces with very high ceilings. Yet another form of direct/indirect lighting uses two entirelydifferent luminaires for the two components, usually direct lighting luminaires and free standing or wall mounted uplighters.

9.4.4 Localised lightingUnlike direct lighting, indirect lighting and direct/indirect lighting, which are most frequentlyused to provide a uniform illuminance across the whole working plane, localised lightingdeliberately sets out to provide non-uniform lighting, with a higher illuminance around theworkstations and a lower illuminance elsewhere. Workstations typically occupy about 25 to 30 percent of office floor area so this approach offers the potential for energy savings but withreduced flexibility unless care is taken to ensure easy movement and reconnection whenworkstations are relocated.


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Localised lighting can take various forms such as luminaires in or suspended from the ceilingabove each work station, or free standing direct/indirect lighting adjacent to a work station, orindirect lighting located in the centre of a cluster of workstations (Figure 9.8).

Luminaires recessed into or surface mounted on the ceiling are usually part of a re-locatableceiling tile system. Suspended luminaires can be connected to a ceiling mounted track system.The direct component of free standing direct/indirect lighting adjacent to the work stationshould ideally be positioned to throw light from either left or right side of the work surface andshould cover the task area with a uniformity ratio of 0.8 or better. Lighting placed in front ofthe task area is likely to produce veiling reflections.

9.4.5 Supplementary task lightingSupplementary task lighting consists of a task light attached to each desk or workstation.Supplementary task lighting is usually designed so that the ratio of task area illuminance to the ambient illuminance is 2:1 as this gives a reasonable balance between visual comfort andenergy savings.

Supplementary task lighting luminaires should allow the occupant some degree of control, bothof light output and position. Control of light output can be provided either by switching ordimming. The position of the luminaire should be limited so as to ensure that it cannot becomea source of discomfort to others. To avoid discomfort to those sitting at the desk, thesupplementary task lighting should not be above sitting eye height. Further, the luminaireshould not be positioned so low that deep shadows are cast across the work area. As a rule ofthumb, the minimum height for the luminaire above the task area should not be less than 0.5 ofthe width of the task area. Task lighting luminaires need to be mechanically and electrically safeand not too hot to touch or work close to.

9.4.6 Cove lightingCove lighting aims to produce indirect lighting by throwing light across the ceiling from a ledgeor recess high up on a wall. This approach has three limitations. First, great care has to be takento avoid the wall immediately above the cove and the adjacent ceiling having a luminancehigher than the maximum luminance limits given in Table 9.7. Second, depending on thecove’s distance below the ceiling it may be difficult to light the ceiling more than 2 to 3 m from the wall. Third, the energy efficiency is low. Apart from in corridors, this method is rarely used in offices today.

Figure 9.8Localised lighting


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9.4.7 Luminous ceilingsLuminous ceilings usually consist of an array of light sources contained above a translucentdiffusing ceiling. The surfaces of the cavity above the ceiling are finished in a high diffusereflectance. The cavity itself has to be high enough for the individual light sources not to bedetectable through the diffusing material. Although luminous ceilings are not a form of indirectlighting, they produce a very similar light distribution. Luminous ceilings vary widely in energyefficiency depending on the transmittance of the diffusing material and the light source used.However, they almost always pose problems for access and maintenance so are rarely used inoffices today.

9.4.8 DaylightRegulation 8(2) of the Workplace Regulations states that ‘The lighting in (every workplace)shall, as far as is reasonable practicable, be by natural light.’ This means that the provision andcontrol of daylight should be considered for every office. Of course, most building footprintsand the fact that daylight predictably fails every night means that reliance can rarely be placedon daylight alone. What is required is a useful combination of daylight and electric light. For acomprehensive guide see SLL Lighting Guide 10: Daylighting and window design. For details ofvarious approaches to combining electric lighting and daylighting in offices see SLL LightingGuide 7: Office lighting. For guidance on some of the factors to consider about daylighting, seeChapter 7 of this Handbook.


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Chapter 10: Industrial lighting

10.1 Functions of lighting in industrial premises

The basic problem of lighting for industry is the wide variability in the amount and nature ofvisual information required to undertake work in different industries. Some industrial workrequires the extraction of a lot of visual information, typically the detection and identification ofdetail, shape and surface finish. Other types of industrial work require accurate eye-handcoordination and the judgment of colour. Yet other types of industrial work can be done withvery little visual information at all. The materials from which visual information has to beextracted can be matte or specular in reflection or some combination of the two, and theinformation can occur on many different planes, implying many different directions of view.Further, the material from which the information has to be extracted can be stationary ormoving. This variability means that the design of industrial lighting is inevitably a matter oftailoring the lighting to the situation. There is no ‘one size fits all’ solution to industrial lighting.

However, there is a limit to how closely the lighting can be tailored. This limit is set by the factthat many different tasks are likely to occur on the same industrial site, within the same building,on the same production line and, certainly, within the area lit by one general lighting installation.The usual solution to this problem is to provide general lighting of the whole area appropriatefor the average level of task difficulty; localised lighting where work is concentrated, e.g. on anassembly line and local lighting where fine detail needs to be seen, e.g. on a lathe in a machineshop, or where obstruction reduces the visibility of the task, e.g. on the work piece of a hydraulicpress, or where there is an obvious hazard, e.g. on the feed to a circular saw. The only placewhere this general/localised/local lighting approach is impossible is where the scale of theequipment is so large that both the people and the lighting work within the equipment, e.g. a chemical plant. For such applications, lighting equipment is integrated into the plant.


Despite the variability faced by the designer of industrial lighting, the objectives are the sameeverywhere. They are:

to facilitate quick and accurate work

to contribute to the safety of those doing the work

to create a comfortable visual environment.

To meet these objectives it is necessary to consider many aspects of the situation.

10.2.1 Legislation and guidanceThere are several different pieces of legislation relevant to industrial lighting, ranging fromstatements of general principle to specific requirements.

Under the Health and Safety at Work Act 1974 the employer must, as far as reasonablypracticable, provide and maintain a safe working environment with adequate lighting.

Under the Factories Act 1961, Section 4, reference is made for the effective provision forsufficient and suitable lighting in every part of the factory in which persons are working orpassing through.


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In Section 8 of the Offices, Shops and Railway Premises Act 1963, reference is made to suitableand efficient lighting, either natural or artificial. Again the need for maintenance is highlighted.

Most associated Regulations and Acts call for adequate lighting and installation maintenance.Some are listed below:

Health and Safety (Signs and Signals) Regulations 1996, (plus BS 5266, EN 1838)

Building Regulations, Part L: Conservation of fuel and power

Building Regulations, Part B: Fire safety

Fire Precautions (Workplace) Regulations 1997

Visual Display Screens Act 1992

Electricity at Work Regulations 1989.

Guidance on lighting for specific industries is given in the SLL Lighting Guide 1: Industrial lighting.

10.2.2 The environmentIndustrial lighting may be required to operate in extremes of temperature and humidity, may beexposed to atmospheres that are corrosive, explosive or dirty, and may need to be capable ofwithstanding water jets and vibration.

Some light sources are temperature sensitive. For example, fluorescent lamps only produce theirfull light output at a specific ambient temperature, higher or lower temperatures causing asignificant reduction in light output. LEDs produce less light output and have shorter lives as theambient temperature increases. Where ambient temperatures are low, for example in a cold store,care is necessary to avoid starting problems with discharge lamps.

Control gear has a maximum operating temperature above which life will be reduced. Electroniccontrol gear is more sensitive than electromagnetic control gear in this respect. Therefore, careshould be taken in selecting and locating control gear when lighting industries where theambient temperature near the luminaires is high, such as in a foundry.

Luminaires designed to cope with damp, corrosive, explosive, flammable or dirty atmospheresare available, at a price. Luminaires capable of operating in damp and dirty conditions areclassified using the International Protection (IP) system (see Table 4.10).

Some industrial activities produce considerable vibration, for example movement of an overheadcrane. Light sources where a hot filament is used are sensitive to vibration.

10.2.3 Daylight availabilityMany industrial premises have the potential to use daylight. For new buildings, this can be donethrough a special roof construction, such as a north light (Figure 10.1). For existing roofs, it issometimes possible to replace existing roof panels with simple translucent panels. The lightingobjective for any daylighting system should be to provide diffuse daylight without direct sunlight.Direct sunlight can cause glare and strong shadows on the workplace and should be avoided.


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Figure 10.1 Daylight provided by a north light roof

10.2.4 Need for good colour visionWhere colour is used to convey information, lighting with good colour rendering properties isrequired. Examples of applications where colour is used in this way are electrical assembly,where components are colour coded; food processing, where colour is used to judge freshnessand suitability for consumption; and printing and painting, where consistency of colour isimportant. For such applications, a light source with a CIE general colour rendering index of atleast 80 is recommended. For some tasks where very fine colour discrimination is required, e.g.grading diamonds, special lighting which enhances the relevant colour differences is used.

Where colours are used to identify the contents of pipes and conduits, it is essential that thelighting should make it easy to identify these colours correctly.

10.2.5 ObstructionMany industrial premises contain obstructions. Obstructions tend to produce shadows.Shadows are cast when light coming from a particular direction is intercepted by an opaqueobject. Shadows can be minimised by:

using a larger number of smaller wattage light sources rather than a smaller number of larger wattage light sources so that light is incident from many directions

using luminaires with a widespread light distribution

having high-reflectance surfaces in the space

providing local lighting of the shadowed area.

Figure 10.2 shows a small workshop where shadows have been minimised by using a largenumber of fixtures and high reflectance surfaces.


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Figure 10.2 A small workshop with highreflectance walls and lit by aregular array of luminaires with awide luminous intensitydistribution. The result is ashadow-free environment.

At the very least, a proportion of the light emitted by luminaires should be emitted upward tobe reflected from a high-reflectance ceiling or roof.

Although shadows can be a problem, it should be noted that they are also an essential elementin revealing the form of three-dimensional objects.

10.2.6 Directions of viewDirections of view in industry can vary widely, from vertically downward into a case wherecomponents are being assembled, through horizontal for work on a press, to upward for a forklift truck driver picking a pallet off the top of a rack (Figure 10.3). This wide variety ofdirections of view means that care has to be taken to avoid both disability and discomfort glare. This can be done by:

using smaller wattage light sources so that the source luminance is lower

using luminaires which do not allow a direct view of the light source

using large area luminaires with an upward light component

having high-reflectance surfaces in the space.

Figure 10.3Directions of view for a fork lift truck driver


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10.2.7 AccessAll lighting installations require maintenance. For this to occur, access is necessary. Whendesigning an industrial lighting installation, it is essential to consider how access is to beachieved without disrupting operations.

10.2.8 Rotating machineryWhere rotating or reciprocating machinery is present a stroboscopic effect is possible. Astroboscopic effect is evident when oscillations in the illumination of a moving object cause thatobject to appear to move at a different speed from the speed it is actually moving or even toappear to be stationary. All light sources operating from an alternating current electrical supplyproduce oscillations in light output. Whether these oscillations are enough to produce astroboscopic effect will depend on the frequency and amplitude of the oscillation. The closerthe fundamental frequency of light oscillation is to the frequency of rotation and the larger theamplitude of light oscillation, the more likely a stroboscopic effect is to occur. The probabilityof a stroboscopic effect occurring can be reduced by:

using high-frequency electronic control gear for discharge lamps

mixing light from light sources operating from different phases of the electricity supply before it reaches the relevant machinery

supplementing the general lighting of machinery with task lighting using a light source with inherently small oscillation in light output, such as an incandescent lamp.

10.2.9 Safety and emergency egressSome consideration of the impact of lighting on safety is appropriate in all lighting applicationsbut it is particularly important in industrial situations. This is because of the complex layout ofmany plants, the hazards associated with some manufacturing processes and the dangers frommoving equipment.

Minimum illuminances are recommended for safety whenever the space is occupied, rangingfrom 10 lx where there is little hazard and a low level of activity to 50 lx where there aredefinite hazards and a high level of activity. But illuminance alone is not enough. Hazardoussituations can arise whenever seeing is made difficult by disability glare, strong shadows andsudden changes in illuminance.

Emergency lighting is required in all industrial premises (see Chapter 8): When designingemergency lighting, it is essential to understand the hazards associated with different operationsso that the appropriate form of emergency lighting can be determined, i.e. which areas can beevacuated immediately, which areas contain operations that need to be shut down beforeleaving, and which areas contain operations that need to be maintained.


There are many different industrial operations but there are also some areas common to manyindustrial premises. These will be discussed here. Details on lighting for a range of specificindustries are given in SLL Lighting Guide 1: Industrial lighting.


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10.3.1 Control roomsControl rooms are often crucial for the production and safe operation of a wide range ofprocesses. Staff monitor and act upon incoming status information (plant, fuel, and productetc.) which is normally displayed on visual display terminals or mimic diagrams (Figure 10.4).The work is often multi-functional and the lighting scheme must enable a wide range of visualtasks to be performed whilst revealing incoming status information with absolute clarity. Thelighting should be as flexible as possible to meet the different visual tasks with general dimmingor alternative switching arrangements and/or local lighting. The luminaires should blend withthe room as far as practical to avoid being sources of distraction. Low glare or shielded, flicker-free high frequency lighting, is preferred where possible.

Figure 10.4Lighting of acontrol room

The lighting designer will need to establish precisely how and where the information will bedisplayed so that the layout geometry and light distribution of the luminaires can be co-ordinated. Often incoming information will be displayed in a vertical or near vertical plane andthe display screen(s) or dial(s) will often be fronted by glass or clear plastic. It is essential toavoid veiling reflections in these displays.

There are three ways to do this:

position downlighter luminaires to avoid the critical luminaire/screen/eye geometry

select downlighter luminaires with low luminance at the critical luminaire/screen/eye geometry (see Table 10.1)

treat the ceiling/upper walls as a low luminance source by uniform uplighting with uplighter luminaires.

Table10.1 Downlighter luminance limits in display screen areas

Screen treatment

Good or moderate treatment (Type 1)

None (Type 2)

Maximum luminance (cd/m2) where somenegative polarity software is used

1000

200


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Where positive polarity software only is being used on Type 1 screens the luminance limit can be increased to 1500 cd/m2.

Where positive polarity software only is being used on Type 2 screens the luminance limit can be increased to 500 cd/m2.

The above limits should be applied to the downlighter elevation angle, which impinges on thescreen at the relevant luminaire/screen/eye geometry. Typically this will be in the range 55 to 85 degrees.

For uplighting, the maximum average ceiling luminance is 500 cd/m2 and the maximum pointluminance is 1500 cd/m2.

Horizontal display screens These will reflect large areas of ceiling and it will often be extremely difficult to plan asatisfactory downlighter scheme, which avoids veiling reflections, leaving uniform lowluminance uplighting or local lighting as the only viable solutions.

When uplighting it is important that the ceiling and upper walls have matte finishes to provide adiffuse reflection. High reflection factors are essential for high efficiency lighting. Uniformceiling luminance is the key objective and it is preferable to use more low output uplightersthan fewer with a high output. Ceiling ventilation grills or other obstructions should be painteda matching finish to the ceiling to avoid luminance imbalances reflected in screens.

Mimic diagramsThese need to be evenly illuminated and the level of illuminance will depend on the detail, theviewing distance, and if the display is self-luminous (where overlighting will wash out theluminous detail). Dimming is advisable and asymmetric ‘wall washer’ luminaires are availablewhich can be surface or recessed mounted.

Room surface luminancesSurface luminances need to be controlled to ensure no excessive contrasts between the screenand other objects within the same field of view, or other items, which are regularly looked at. Ingeneral, light coloured matte finishes are preferable for all room surfaces and furnishings.

Windowed control rooms These often provide operatives with an essential view of the processes under control. As withdisplay screen lighting it will be necessary to avoid veiling luminaire reflections in the glass andthe same principles will apply. Reflections of room surfaces must also be controlled, especially ifthe average luminance outside the control room is significantly lower than within. Dimmingcontrols will often be necessary to provide the requisite balances.

Emergency lightingThis deserves careful consideration in control rooms, since high-risk processes may need to becontinued or shut down in the event of an emergency. This may require lighting levels inexcess of the normal escape route levels, even up to 100% of the normal lighting levels. In thesecircumstances it is often necessary to consider uninterruptible power supplies to the lightingrather than self contained battery operated luminaires which only deliver a relatively low light output.


Average illuminance (lx)

300

500

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Table 10.2 Lighting recommendations for direct lighting in control rooms

10.3.2 StorageMany industrial premises contain areas where raw materials or finished product are stored. Insuch areas, many visual tasks are performed on vertical surfaces at different heights (Figure10.5). The lighting designer will require a lot of information regarding the movement of goodsand proposed stocking arrangements if all the lighting needs are to be met. In particular, thelocation of fixed items such as racking is critical, as luminaire layouts must be plannedaccording to the layout of the aisles.

Activity

Display screen tasks, self-luminous mimic diagrams

Paperwork tasks, general display boards

Low contrast mimic diagrams

Minimum colourrendering index

80

80

80

Maximum unifiedglare rating

19

19

19

Figure 10.5 Lighting of astorage area

Luminaires are available with optics tailored to the requirements of high rack lighting (> 5 m).These luminaires have a high downward luminous intensity to maximise penetration into theaisles. A sharp cut-off in transverse plane ensures minimal light waste on the tops of racks and a broad axial light distribution maximises luminaire spacing along the aisles.

In ‘concertina’ storage mechanisms (bins or racks which push together to reveal access aisles)continuous fluorescent trough reflectors are mounted above the bins and at 90 deg to the aisleopenings. Consideration should be given to localising the lighting according to occupation ofthe access aisles, e.g. pull cord switching or presence detection controls. This will avoid wastedenergy due to all the luminaires being needlessly switched on.

With random bulk storage it is best to use wide distribution luminaires in a closely spaced array. This will help to minimise the effects of shadows due to stacking and maximise vertical illuminance.


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30

25

25

22


40

60

80

80

Minimummaintained

illuminance (lx)

20

150

200

300

Activity

Automated aisles

Manned aisles

Continuously occupied areas withlittle perception of detail required

Continuously occupied areas withperception of detail required

Cold stores should be illuminated with luminaires which are reliable and efficient at thetemperatures concerned. Advice from manufacturers should be sought before luminaires are specified.

Automated picking warehouses need only sufficient lighting for safe access. However, anymaintenance work will need additional portable lighting.

Direct glare from luminaires can be particularly problematic, especially for forklift truck drivers.The selection of a greater number of low luminance luminaires is preferable to a smallernumber of high luminance luminaires. Fitting louvres or diffusers can help but maycompromise the light distribution. Uplighting onto a reflective ceiling background will reducethe brightness contrast between the source and background to lessen direct glare. This may beachieved by selecting downlighter luminaires with an upward light component, or by secondaryuplighting. Reflected glare from floors etc. can also be problematic and matte should always beused in preference to glossy finishes.

Table 10.3 Lighting recommendations for storage areas

10.3.3 Ancillary areas CirculationWhen lighting circulation areas such as corridors or stairs, visual guidance is as important asilluminance. Care should be taken to ensure sufficient light is directed onto the walls therebypreventing the corridor appearing oppressive.

Luminaires should be positioned in stairways so as to provide sufficient contrast between thetreads and the risers. Provision should be made for emergency lighting in all areas, particularlythose defined as escape routes. The reader should consult SLL Lighting Guide 12: Emergencylighting design guide.

Canteens and mess rooms Many ancillary areas can be illuminated with a regular array of luminaires. However, some areassuch a receptions, canteens and rest rooms benefit from a more imaginative approach, therebycreating a better visual impression. In these situations the recommended illuminances shouldonly be treated as a guide — the ‘feel’ of the lighting is far more important than theillumination level achieved.



22

22

22

25


80

80

80

60

Minimummaintained

illuminance (lx)

100

100–300

300

100

Area

Lifts, corridors and stairs, toilets

Mess rooms

Canteens

Plant rooms, store rooms

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Table 10.4 Lighting recommendations for ancillary areas

10.3.4 Speculative factory unitsSpeculative factory units are typically simple shed-type buildings. Often these are built before a tenant is found, and therefore there is no knowledge of what the building will be used for.

Typically the lighting is provided by a combination of daylight and electric light. Roof lightsusually provide the daylight, supplemented by general lighting from a regular array ofluminaires. The purpose of the electric lighting is to illuminate the space uniformly, usingconventional equipment. Extreme conditions such as high temperature, high dust levels etc.are not catered for.

Table 10.5 Lighting recommendations for speculative factory units


22


60

Minimummaintained

illuminance (lx)

300

Activity

Workshop units

10.4 Approaches to industrial lighting

Industrial lighting usually consists of some combination of general lighting, localised lightingand local lighting. For some visual inspection tasks, special lighting arrangements are needed toreveal what is being sought.

10.4.1 General lightingGeneral lighting is designed to produce a uniform illuminance on the working planethroughout the area involved. A minimum illuminance uniformity of 0.8 is recommended.General lighting is usually provided by a regular array of luminaires. This approach offersconsiderable freedom in the location of workbenches and machinery. The choice of light sourceto be used for general lighting is influenced by the level of colour rendering required and themounting height. Some examples of the level of colour rendering required are given in Section10.3. The influence of available mounting heights is shown in the Table 10.6. The lower themounting height, the greater the care that needs to be taken to control glare. Where commonviewing directions are upward towards the lighting installation, large area, low luminanceluminaires should be used. Where linear fluorescent luminaires are used, orienting theluminaires to run parallel to the direction of view and at right angles to rows of workbenches or machines is usually the best layout.


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Mounting height (m)

2.5 to 3.0

3.0 to 6.0

Above 6.0

Usual light source

Fluorescent

Fluorescent or low wattage, high pressure discharge

High wattage high pressure discharge

10.4.2 Localised lightingLocalised lighting is characterised by higher illuminances in one part of a workshop and lowerilluminances in another. Localised lighting is appropriate where the arrangement of workpositions is permanent and the visual demands of the work are different in different areas,where there is large scale obstruction to general lighting or where the visual demands of thework call for additional illumination or a different light distribution.

10.4.3 Local lightingLocal lighting is designed to illuminate the task and its immediate surround. Local lightingshould be regarded as a supplement to general lighting or localised lighting, not a substitute.Local lighting can be fixed or adjustable by the worker.

10.4.4 Visual inspectionRapid visual inspection calls for off-axis detection of defects. How well this can be done willdepend on the visibility of the defect and, if there are other objects in the area to be searched,the conspicuity of the defect. There are many different methods of lighting for visualinspection. All depend on the use of lighting to make the defect more visible and moreconspicuous. Figure 10.6 shows some arrangements for revealing different features of products.

Table 10.6 The usual light sources used for general lighting at different mounting heights


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Figure 10.6 Examples of lighting for visual inspection

(a) To prevent veiling reflections, light must not coincide with angle of view.(b) The observation of specular detail on a diffuse background is aided if reflected light does coincide with angle of view.(c) Low-angle lighting used to emphasise surface irregularities.(d) Reflected light from a source having a large surface area facilitates detection of blemishes in a polished surface.(e) Diffuse lighting from an extended source aids typesetting.(f) Irregularities in transparent materials are revealed using a transmitted light from a diffuse source.(g) Silhouette is an effective means of checking contour.(h) Directional lighting is needed to reveal form and texture.

(a) (b) (c)

(d) (e)

(f)

(g) (h)

10.4.5 Visual aidsThere are some features of products that can be much more easily seen with the use of visualaids. Such aids include magnifiers, stroboscopes and ultraviolet lamps. Magnifiers can behead mounted or hand held. Magnifiers are useful for inspecting very fine detail but there isa trade-off to be made against field size. The greater the magnification, the smaller is the fieldsize. The lowest magnification necessary to see the required detail should be used.

It is sometimes necessary to examine machined parts while they are in motion. A stroboscope will help with this by apparently stopping the motion. To do this is it isnecessary for the frequency of the stroboscope to be adjustable so that it can be matched to the frequency of motion. Seals can be tested by placing a fluorescent dye in the sealedcontainer and searching for leaks using an ultraviolet lamp.


Chapter 11: Lighting for educational premises

11.1 Functions of lighting for educational premises

Educational premises contain spaces with many different functions. For schools, these can rangefrom the ubiquitous classrooms through the assembly hall to specialist locations such as artrooms and sports halls. For universities, there are lecture halls with raked seating, researchlaboratories and seminar rooms. The lighting of educational premises should be both functionaland inspirational. Functionally, the lighting should allow the students to see the teacher and theteacher to see the students. For inspiration, the lighting should be consistent with thepsychological and emotional needs of the students.

Guidance on the lighting of some parts of educational premises is given elsewhere in thisHandbook, e.g. for the lighting of sports halls and swimming pools see Chapter 19, foremergency lighting see Chapter 8. More guidance on the lighting of educational premises ispublished by the Department for Children, Schools and Families in the form of BuildingBulletins and is given in the SLL Lighting Guide 5: Lecture, teaching and conference rooms. Thelighting that will be considered here is that of the functional parts of educational premises, suchas classrooms and lecture halls.


11.2.1 Students’ capabilitiesThe policy today is to educate many students with disabilities in conventional schools. Thismeans that a classroom may contain students with seeing and hearing difficulties or who areautistic and therefore sensitive to sudden changes in the environment. For students who havedifficulty hearing, it is important that the movements of the teacher’s lips are clearly visible. Forstudents who are partially sighted, it is important to control glare from luminaires andwindows, to minimise veiling reflections and to use the décor to give high contrast to salientdetails of the environment, such as the position of the door (Figure 11.1). For autistic children,it is necessary to avoid sudden and dramatic changes in the environment. This implies that slowdimming control is better than simple switching and that control of any changes should residein the classroom so students can be warned about any changes. More advice is given inDepartment for Education and Science Building Bulletin 77.

Figure 11.1 A classroom with goodluminance and colourcontrast on salient detail

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11.2.2 Daylight or electric lightMost school premises make extensive use of daylight yet electric lighting is always installed foruse after dark and to supplement daylight in some parts of the space. Daylight should be usedwhenever it is available provided it is available without causing visual or thermal discomfort.This means that care has to be taken to control the admission of sunlight (see Chapter 7). Also,if electric lighting is used during daytime, it should be fitted with a control system that willminimise its use of energy.

11.2.3 Common lines of sightFormal teaching spaces have common lines of sight. For example, the lines of sight in a lecturehall are commonly from the seating towards the lecturer’s podium, demonstration bench andprojection screen, and from the lecturer towards the seating area. These common lines of sightallow the lighting designer to pick the location and shielding of luminaires and windows so asto eliminate glare (Figure 11.2).

Figure 11.2 Common lines of sight in formal teaching spaces

11.2.4 Flat or raked floorSmall rooms in educational premises almost invariably have a flat floor but large lecture hallsoften have a raked floor. The problem these pose is that the effective height of the roomdecreases from the front to back of the lecture hall and this will influence the spacing of theluminaires if a constant illuminance is to be provided.

11.2.5 Presence of visual aidsToday, the ‘chalk and talk’ approach to instruction is often supplemented by visual aids usingtelevision and computer screens or projected images. Uncontrolled lighting, both daylight andelectric light, can make it difficult to see these aids. The presence of such aids makes itnecessary to be able to dim the lighting of the classroom and to control the admission ofdaylight, particularly where daylight falls directly on the screen (see Section 11.3.3).

11.2.6 Surface finishesWhile strongly coloured surfaces can be stimulating, their use in classrooms should be limitedto small areas (LRC, 1998). The majority of classroom surfaces should be finished in lowchroma, high reflectance materials. This will increase the amount of inter-reflected light which,in turn, will distribute daylight more evenly across the room, and reduce the strength of anyshadows and veiling reflections.


Maximum unified glare

rating

19

19

19

19

22

19

19

19

19

19

Minimumilluminanceuniformity

0.8

0.8

0.8

0.8

0.8

-

-

0.8

-

-

Minimummaintained

illuminance (lx)

300

500

300

500

500

300

300

300

300

300

Room

Classroom, lecture hall

Classroom used for adult education

IT room

Arts room

Science laboratory

Seminar room

Library

Assembly hall

Music room

Drama studio

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11.3.1 IlluminancesTable 11.1 summarises the minimum maintained illuminances recommended for the morecommon functional areas of educational premises. These illuminances should be provided onthe relevant plane. For classrooms, this will be on the plane of the desks but for art rooms itmay be the vertical plane of a canvas. High reflectance surface finishes will help distribute thelight evenly on different planes.

Table 11.1 Lighting recommendations for functional areas

Minimum CIEgeneral colour

rendering index

80

80

80

90

80

80

80

80

80

80

11.3.2 Illuminance uniformityIlluminance uniformity is important where the lighting needs to be perceived as uniform orwhere activities may take place anywhere within the lit area. So, for classrooms, lecture halls, ITrooms, art rooms, science laboratories and assembly halls a minimum illuminance uniformityof 0.8 is recommended. Where the space is likely to be obstructed, e.g. a library or where lightshould be centred on a performer, e.g. in a music room, the illuminance uniformityrequirement is limited to the task area. Even where illuminance uniformity over the wholeworking plane is important, it may be necessary to provide additional lighting in a specific areato give emphasis e.g. on the whiteboard in a classroom.

11.3.3 Glare controlGlare control should be applied to both luminaires and windows. For luminaires, this is amatter of limiting the light distribution so that the unified glare rating is 19 or less. One pointthat calls for care is the lighting of the teacher in a classroom or an instructor in a lecture hall.Figure 11.2 shows an instructor being illuminated with spotlights. The instructor willexperience glare if the spotlights are positioned less than 60 degrees above the line of sightstraight ahead.


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For windows, what is required is an ability to shut out a direct view of the sun and sky,preferably while leaving some view out.

11.3.4 Light source colour propertiesLight sources with a CIE general colour rendering index (CRI) of at least 80 should be usedin all functional parts of a school. For circulation areas, light sources with a CRI of at least 60 are acceptable.

As for colour appearance, the correlated colour temperatures (CCT) of light sources commonlyused in schools varies from 3,000 K to 5,000 K and sometimes as high as 6,500 K. CCTs at thelower end of this range will give a warm appearance to the interior but do not blend well withdaylight. Higher CCTs will blend better with daylight but give a cool colour appearance to thespace. Very high CCTs will also produce a perception of greater brightness for the sameluminance and enhance visual acuity. Whatever light source CCT is chosen, it should be usedthroughout the school.

11.3.5 Control systemsLighting controls should be installed in educational premises for three purposes:

to minimise the use of electricity when there is sufficient daylight available

to avoid the waste of energy by turning off the lighting when the space is empty

to provide some flexibility in the use of the space.

To minimise the use of electricity when there is sufficient daylight available, it is necessary towire the installation so that luminaires at the same distance from the windows can be switchedor dimmed together (Figure 11.3). Ideally, a dimming system should be used with aphotosensor to detect the amount of daylight available.

lamps off one lamp on both lamps on

total illumination

electric light contribution

daylight contribution

Figure 11.3 Balancing daylight and electric light in a classroom

To avoid the waste of energy by turning off the lighting when the space is unoccupied, motionsensors with an automatic switch off and a manual switch on should be used. To provide someflexibility in the space, a switching or dimming system should be provided under the control ofthe teacher or instructor.


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11.4 Approaches to lighting educational premises

11.4.1 Classrooms and lecture hallsClassrooms can be used for formal or informal teaching. Lecture halls are solely for formalteaching. In formal teaching, the students are all looking towards the teacher and thewhiteboard or screen. In informal teaching, the students may be working in groups with theteacher circulating amongst them or the whole class may be arranged around the teacher.

For classrooms used for formal teaching, a regular array of direct or direct/indirect fluorescentluminaires can be used, the long axis of the luminaires being arranged parallel to the windows.The use of direct/indirect luminaires is specifically recommended in some of the DCSF(formerly DfES) Building Bulletins. The whiteboard should be provided with its own lightingsystem designed to eliminate glare and veiling reflections. This can be done by mountingfluorescent luminaires on the ceiling, shielded from the students and located so that the lightreaches all parts of the board at an angle of less than 30 degrees from the plane of the board.The teacher needs to be able to control the lighting. The windows should be fitted with blindsto facilitate the use of visual aids.

Lecture halls often have raked seating and very little daylight. A regular array of dimmableluminaires shielded from students and arranged parallel to the seating is appropriate (Figure11.2). The lighting of the instructor, any demonstration bench and the whiteboard should beprovided by a separate installation. Both installations should be dimmable and under thecontrol of the instructor.

For classrooms dedicated to informal teaching, flexible lighting is desirable. This can take theform of a low level of ambient lighting from a regular array of fluorescent luminairessupplemented by dimmable spotlights mounted on track.

11.4.2 IT roomThe IT room is characterised by the installation of many computer screens for use by students(LRC, 2001a). The lighting of this room faces the same problems as a modern office andtherefore should be lit in the same way, particularly as regards the methods used to minimisehigh luminance reflections from computer screens. The only difference is the need for thestudents to see a projected image of the instructor’s screen. This need implies that the lightingshould be dimmable by the instructor.

11.4.3 Arts studioArts studios have three special lighting requirements; good colour rendering, an emphasis onlighting vertical as well as horizontal planes to ensure good modelling and some flexibility incontrol (LRC, 2001b). Ideally, the windows in an arts room should deliver large amounts ofnorth sky daylight. The electric lighting should blend with north sky daylight and should have aCIE general colour rendering index greater than 90. Both good modelling and flexibility can bedelivered by an installation consisting of a low level of ambient lighting from a regular array offluorescent luminaires supplemented by aimable and dimmable spotlights mounted on track.

11.4.4 Science laboratoriesScience laboratories require special lighting in that the atmosphere may be humid andcorrosive. Luminaires should be sealed and proof against dirt and damp to IP44 (see Table4.10). The electric lighting in a science laboratory should provide the required illuminanceuniformly over the horizontal working plane. Supplementary task lighting may be needed.


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11.4.5 Seminar roomThe seminar room is rather like a small classroom used for informal teaching. The key word asfar as the lighting is concerned is flexibility. This can take the form of a low level of ambientlighting from a regular array of fluorescent luminaires supplemented by dimmable spotlightsmounted on track. At least one line of track on a separate control circuit should run parallelwith the front of the room so that a more formal presentation can be made when desired.

11.4.6 LibraryThe lighting of library spaces must be co-ordinated but appropriate to a number of differentfunctions. In addition to general lighting, lighting for vertical book stacks, lighting for study,lighting for using computers and accent lighting for display purposes may be required. It isimportant that the lighting arrangements are designed so that there is no conflict between theappearance of the different parts of the installation or with the light distribution throughout the space.

11.4.7 Assembly hallThe assembly hall is the one place where the whole school meets. As such it has an importantsocial function. It may also be used for school ceremonies, concerts and theatrical performancesas well as community events (LRC, 2001c). The general lighting should be designed to provideuniform illumination over the main seating area, using dimmable luminaires that blend withthe architecture. Luminaires with louvres should not be used as they often vibrate duringmusical events. The stage should be lit using theatrical lighting techniques.

11.4.8 Music roomMusic rooms require illumination on many different planes, depending on the instrumentbeing played, the position of the score and the location of the instructor. Daylight is desirableprovided it does not cause glare and is evenly distributed around the room. Suspendeddirect/indirect lighting in a room with high surface reflectances is a good approach. Luminaires with louvres should not be used as they may vibrate during performances.

11.4.9 Drama studioThe drama studio is essentially an open space in which different types of activity occur. Theprinciple requirement for the lighting is variation in position, light distribution and amount. A series of mounting bars and a stock of theatrical lights combined with a control desk willprovide the necessary flexibility. Ambient lighting using surface mounted fluorescent luminairesis also required for setting up and cleaning up.


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Chapter 12: Retail lighting

12.1 Functions of retail lighting

For the retailer, lighting is an essential part of ‘setting out the stall.’ Lighting has four major rolesin retail premises. They are:

to attract attention

to send a message to would-be shoppers about the nature of the shop

to guide shoppers around the shop

to display the merchandise to advantage.

Subsidiary lighting systems are needed to provide security after closing and to facilitate egress inan emergency (see Chapter 8). Examples of retail lighting design are available in Turner (1998).


12.2.1 Shop profileRetail premises differ on four dimensions: price, usage, range of products and sales style. It is theposition on these four dimensions that determine the shop profile. Table 12.1 indicates the mostcommon shop profiles.

Table 12.1 Four common shop profiles

Shop profile

Low budget

Value for money

Quality

Exclusive

Prices

Bargain

Low

Higher

Expensive

Usage

Weekly

Daily

Impulse

Deliberate

Product range

Wide

Limited

Wide

Exclusive

Sales style

Self service

Social contact

Shopping as fun

Personal service

Shop profiles matter because different profiles have different lighting styles. Low budget shopstend to be big box stores using high level uniform general lighting with no accent or displaylighting (Figure 12.1). Exclusive shops tend to be much smaller and use low levels of generallighting combined with strong accent and/or display lighting on the merchandise (Figure 12.2).Value for money and quality shops lie between these extremes, with both general lighting andsome accent lighting being used.


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Figure 12.1 A budget retail store

Figure 12.2A ‘high end’ retail outlet

12.2.2 Daylight or electric lightMany retail premises do not allow much daylight penetration into the shop so this question ismoot. However, in many out-of-town ‘shed’ stores, daylight may be admitted through rooflights. The use of daylight adds an attractive dynamic element to the store.

12.2.3 Nature of merchandiseThe type of lighting and the colour properties of the light sources used depend on the nature of the merchandise. Merchandise, such as bedding, needs to be displayed in a warm, cosyatmosphere. This calls for low light levels and a warm colour appearance. Conversely, freestanding white goods are best shown at high light levels with light of a cool colour appearance,although when incorporated into displays simulating a home setting, lighting that looks likeattractive home lighting is desirable. Merchandise such as meat, fish, fruit and vegetables needslighting that emphasises whatever characteristic indicates freshness, e.g. redness for meat.Therefore, understanding the nature of the merchandise is essential when designing retail lighting.

12.2.4 ObstructionSome stores, such as DIY stores, have more in common with warehouses than shops. The storeis divided into a large number of aisles and the merchandise is displayed in racks extending tohead height and above. Where obstruction occurs, it is essential that the layout of the lightingand the merchandise is coordinated.


12.3.1 IlluminancesRetail lighting is essentially a balance between general lighting, accent lighting and displaylighting. This balance itself depends on the shop profile. Therefore, the illuminances to be useddepend on the shop profile. For low budget shops, where there is no accent or display lighting,the average illuminance should be in the range 500 to 1000 lx. This illuminance should beprovided on the merchandise. For a supermarket, this means on the vertical faces of the shelves.


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Strength of accenting

None

Noticeable

Low theatrical

Theatrical

Dramatic

Very dramatic

For a shop with an exclusive profile, which means the widespread use of accent and displaylighting, the average general lighting illuminance should be in the range 100 to 200 lx. Thislower illuminance is necessary for the accent lighting to be effective and should be provided on a horizontal plane at counter level.

For shops with value for money and quality profiles, where some accent lighting is used, theaverage general lighting illuminance should be in the range 250 to 500 lx and should be provided on the merchandise.

12.3.2 Illuminance uniformityRegardless of the shop profile, general lighting should be uniform. An illuminance uniformity(minimum/average) of at least 0.7 should be achieved by the general lighting alone. Whereaccent and display lighting is used, the overall illuminance uniformity is low, by design.

12.3.3 LuminancesFor accent lighting to be effective, the luminance of the merchandise lit has to be higher than the luminance of its immediate background. Different luminance ratios will give differentstrengths of highlights and shadows. Table 12.2 indicates the luminance ratio for differentstrengths of accents.

Table 12.2 Luminance ratios for different strengths of accent lighting

Luminance ratio (accent/background)

1

2

5

15

30

> 50

12.3.4 Light source colour propertiesThe colour appearance of the light used in a shop will contribute to the message the lightingsends to would-be shoppers. A cool light appearance tends to convey a business-likeatmosphere while a warm colour appearance indicates a homely feel. As a general rule, thecolour appearance of the light sources used changes from cool to warm as the shop profilemoves from low budget to exclusive. Where daylight is used in the shop it is necessary tochoose a light source colour appearance that blends well with it. For some merchandise, thecolour appearance of the light used is important. Chiller cabinets look fresher and white goodslook crisper and cleaner under a cool light source. Conversely, gold looks more attractive whenilluminated by a warm light source.

The other aspect of light source colour properties that needs attention is colour rendering. In general, light sources with a CIE general colour rendering index greater than 80 should beused in retail premises.


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This will often be satisfactory but where the merchandise is most likely to be seen underdifferent lighting, e.g. a coat is most likely to be seen under daylight, it is wise to use lightingthat does not distort the colour of the merchandise relative to how the merchandise will be seenin use. For some retailers, there can be a temptation to choose a light source that enhances theappearance of the merchandise. An example is the notorious butcher’s lamp, a lamp thatexaggerates the redness of meat. This is a temptation that should be resisted. In other shops itwill be important to choose a light source with colour rendering properties that give anappealing appearance to human skin, particularly in areas where an individual’s appearance maybe closely examined, e.g. fitting rooms. While the CIE general colour rendering index is auseful guide, the final choice of light source is best made by viewing the lit objects of interest.

12.4 Approaches to retail lighting

12.4.1 General lightingGeneral lighting in shops with a low budget or value for money profile is usually provided froma regular array of luminaires (Figure 12.1). These luminaires range from bare fluorescent lampbattens through recessed fluorescent louvres to pendant metal halide globes. The purpose ofsuch general lighting is to produce a uniform illuminance over the relevant plane without causing glare.

In shops with quality or exclusive profiles, the architecture is more likely to be a feature of thestore and the general lighting will need to be integrated with it. This may involve the use ofrecessed downlights, cove lighting or suspended uplights rather than a regular array (Figure12.2). Regardless of the lighting approach used, the appearance of the luminaires needs to beconsistent with the style of the shop.

12.4.2 Accent lightingAccent lighting is designed to provide additional illuminance on some areas so as to emphasisespecific items of merchandise and to provide a meaningful variation in brightness and shadowthroughout the store. If well done, accent lighting can guide shoppers through the shop anddraw their attention to merchandise. The best form of accent lighting depends on the area to be accented.

For large area wall displays, wall washing luminaires fitted with fluorescent lamps are used(Figure 12.3). For gondola displays, the lighting can be built into the gondolas (Figure 12.4).For small area accent lighting, aimable spotlights attached to power track should be used (Figure12.5). Whatever the form of accent lighting, some flexibility is required. This is because thenature and aiming of accent lighting will depend on the merchandise to be accented. As thenature and layout of the merchandise changes, the accent lighting will need to change.

Figure 12.3Luminaires providingvertical illuminance


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Figure 12.5A shop lit using spotlights on track

Where wall washing luminaires are used, the important characteristic of the luminaires is thelight distribution, the ideal being a uniform illuminance from the top to the bottom of the wall.A similar consideration applies to accent lighting built into gondolas. The illuminancedistribution from the top to the bottom of the gondola should be as even as possible. Wherespotlights are used, the luminous intensity at the centre of the beam, the shape and dimensionsof the resulting light spot with respect to the size and shape of the area to be lit are important.

Accent lighting in shop windows has competition from daylight reflected from the windowglass and from the windows of nearby shops. Depending on the shielding from daylight and thelighting of adjacent shops, the general lighting of the window during the day needs to be in therange 500 to 2000 lx, while accent lighting needs to be in the range 3000 to 10,000 lx. Theseilluminances should be reduced after dark.

12.4.3 Display lightingThe function of display lighting in shop windows is to gain the attention of passersby and tomake the merchandise look attractive. Inside the shop, the main purpose of display lighting is toemphasise the desirable features of specific merchandise. Inside the store, display lighting canbe applied to merchandise open to examination (Figure 12.6) or to merchandise in showcases.

Figure 12.4Lighting of agondola in a shop


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Figure 12.6Display lighting formannequins

Display lighting is designed to gain attention by using an appropriate combination of brightness,colour and modelling. Relative brightness can be expressed in terms of the luminance ratiosgiven in Table 12.2. The higher is the luminance ratio, the more likely the display is to gainattention. As for colour, strongly coloured light on an object of the same colour will deepen thecolour whilst strongly coloured light on the background and surroundings will change theatmosphere. The modelling achieved depends on the relative strength of light delivered fromdifferent directions. Modelling is usually achieved by some combination of key-light, fill-light,back-light and up-light. Table 12.3 describes these techniques.

Table 12.3 Descriptions of the components of display lighting

Light

Key-light

Fill-light

Back-light

Up-light

Description

The principle source ofdirectional illumination

Supplementary illuminationfrom a different direction

Illumination from behindand usually above

Light accentuating parts ofthe display close to the floor

Function

To create sparkle and reveal texture

To soften shadows so as to get thecontrasts in the display at the desired level

To separate the object from itsbackground, to reveal transparent elements

To soften shadows, can be used fordramatic effects


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Different materials require different display lighting techniques. Table 12.4 lists some of themore common techniques for specific materials.

Materials

Uniformly transparent materials

Glass and crystal

Transparent fibrous objects, e.g. fine textiles

Precious stones and jewellery

Opaque, shiny objects, e.g. silver

Opaque, textured objects

Display lighting technique

Transmitted light from a lit background; up-lighting possibly in colour

Highlighting; up-lighting possibly incombination with translucent background

lighting; coloured light

Contour lighting from behind

Small spotlights, black velvet background

Spotlights, black velvet background, highlighting

Light predominantly glancing across the surface

Table 12.4 Common display lighting techniques for particular materials


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Chapter 13: Lighting for museums and art galleries

13.1 Functions of lighting in museums and art galleries

Museums and art galleries come in many different forms, ranging from historic buildings topurpose-built facilities. Likewise, the objects they contain come in many different forms. Someare freestanding, some are wall mounted, some are contained in showcases and some are thereto be experienced. Despite this diversity, the lighting of all types of museums and art gallerieshas five functions:

to display the objects to advantage

to minimise the damage done to the objects by exposure to light

to show off the architecture of the facility

to help maintain the security of the facility

to provide assistance for egress in an emergency situation.

Guidance on all these topics is given elsewhere (Loe et al, 1982; Phillips, 1997; Cuttle, 2007).


13.2.1 Daylight or electric lightOne of the first decisions the designer of lighting in a museum or art gallery has to take is whatbalance should be struck between daylight and electric light. For some exhibits, such as light art,daylight has to be excluded. For others, such as sculpture, daylight is preferred but thewidespread use of daylight can be in conflict with conservation if the exhibits are sensitive tolight. One compromise that is often used is to provide daylight and a view out through alcovesoff the main display areas. When it is decided to use daylight as the primary light source, it isimportant that the designer should preserve the most attractive features of daylight, namely itschanges in amount and colour. There is little point in controlling daylight so closely that itcannot be distinguished from electric lighting. Electric lighting will always be required for useafter dark but can be adjusted during daytime when sufficient daylight is available (see Section 7.2).

13.2.2 Conservation of exhibitsExposure to light can cause damage to objects by radiant heating and by photochemical action.Radiant heating causes surface layers to expand and moisture in the object to be driven out.This results in cracking and lifting together with a loss of colour. Photochemical action is achemical change produced by the absorption of photons. Symptoms of photochemical damageare pigment colour changes and loss of mechanical strength.

The obvious first step to minimise such damage to exhibits is to shield them from both ultra-violet and infrared radiation. This radiation does not contribute to vision but does causedamage. The strongest source of ultra-violet radiation per lumen of light is daylight, even afterpassage through glass. The strongest sources of infrared radiation per lumen of light are theincandescent light sources. All sources of light should be filtered to minimise ultra-violet andinfrared radiation unless required for display purposes.


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But radiation in the visible range can also cause damage particularly at the short wavelength endof the visible spectrum. To minimise damage from light, it is necessary to limit the lightexposure. Table 13.1 shows the limiting illuminances and limiting annual light exposuresrecommended for objects with different levels of responsivity to light. Determining theresponsivity of an object to light is the responsibility of the conservator. An illuminance of 50 lxis considered to be a minimum for displaying objects that require the perception of detail andcolour. For high responsivity objects, using an illuminance of 50 lx implies restricting theannual hours of display to less than 300 hours.

Table 13.1 Limiting illuminance (lx) and limiting exposure recommendations for objects withdifferent levels of responsivity to light

13.2.3 Light source colour rendering propertiesElectric light sources vary in their ability to render colours accurately. Light sources with a CIEgeneral colour rendering index greater than 80 should be used in all museums and art galleries.However, the CIE general colour rendering index is a single number describing a complexperception. Therefore, it is always advisable to view the objects to be displayed under theproposed light source before choosing the light source.

13.2.4 AdaptationThe low light levels in the exhibit rooms of many museums and art galleries mean that visitorsneed time for their vision to adapt from the higher light levels usually present in entrances,cafes etc. To achieve this there should be a transition zone of slowly decreasing illuminancebetween the brighter lit areas and the exhibit areas.

13.2.5 BalanceThe balance between the lighting of the exhibits and the general lighting of the space can varywidely. At one extreme is the approach where the only lighting is the lighting of the exhibits,the general lighting of the space being achieved by spill light from the exhibits (Figure 13.1).Such lighting can be very dramatic but may pose problems for circulation. At the other extremeis a high level of diffuse ambient lighting without emphasis on the exhibits (Figure 13.2). Thisapproach can be very bland. A reasonable compromise is to aim for an illuminance ratiobetween exhibit lighting and ambient lighting of 3:1. If a strong emphasis on the exhibits isrequired an illuminance ratio of at least 10:1 is suggested.

Limiting annual lightexposure (lux-hours/year)

15,000

150,000

600,000

Unrestricted

Limitingilluminance (lx)

50

50

200

Unrestricted

Responsivity to light

High responsivity objects, e.g. silk, newspapers, some colorants

Moderate responsivity objects, e.g. textiles, furs, lace, fugitive dyes, prints, watercolours,

some minerals, feathers

Low responsivity sensitive objects, e.g. oilpaintings, wood finishes, leather, some plastics

Irresponsive objects, e.g. metal, stone, glass,ceramic, most minerals


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13.2.6 Shadows and modellingThe distribution of light around a three-dimensional exhibit determines the strength and formof the shadow pattern created and hence the strength of modelling. A large area luminaire and ahigh surface reflectance background will, together, minimise shadows and modelling. A narrowbeam spotlight and a low reflectance background will, together, maximise shadows andmodelling. What strengths of shadows and modelling are desired is a matter of judgment butexhibits with some modelling are considered more interesting and more attractive than thosewith none (Mangum, 1998).

13.2.7 GlareThe widespread use of spotlights in museums and art galleries makes glare a distinct possibility.Glare from spotlights can usually be avoided if spotlights are aimed not more than 35 degreesabove the downward vertical.

13.2.8 Veiling reflections and highlightsObjects on display can vary dramatically in their reflection properties. A few are diffuse inreflection but many have a strong specular component. This means that high luminancereflections can be seen in the objects. The most usual sources of high luminance in a museumor art gallery will be windows and luminaires. Whether such high luminance reflections aredesirable will depend on the object. For paintings and information presented on computermonitors, high luminance reflections are called veiling reflections and will reduce visibility. For silver and glass objects, high luminance reflections are called highlights and are essential forrevealing the nature of the material.

Whether high luminance reflections are present or absent will depend on the geometry betweenthe luminaire, the object and the observer. By careful selection of the location of the luminairerelative to the object and control of its light distribution, high luminance reflections can beminimised or maximised.

13.2.9 Out-of-hours activitiesPrior to opening and after closing, there are numerous cleaning and curatorial activities thatneed to be undertaken. During this time, the display lighting should be extinguished and themuseum and gallery lit by energy efficient ambient lighting. This is required by Part L of theBuilding Regulations for energy saving reasons.

Figure 13.1General lighting of exhibitspace with spill lighting

Figure 13.2A high level of diffuseambient lighting


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Further, extinguishing the display lighting will help to conserve those objects responsive to light exposure.

13.2.10 Security and emergencyThe objects contained in museums and art galleries are frequently valuable so the security ofthe building is important. Different security systems require different lighting. Where patrollingafter closing is in use, lighting systems that enable the guard to move safely and effectivelythrough the spaces is necessary. A minimum illuminance at floor level of 20 lx should beprovided for safe movement. Museums and art galleries are open to the public, many of whommay be unfamiliar with the layout. Emergency lighting to help with egress, should it benecessary, is required by law (see Chapter 8).

13.2.11 MaintenanceFor any lighting system to be effective it has to be maintained. Access for maintenance needs tobe considered when designing the lighting of museums and art galleries, as it may not beconvenient to move exhibits.

13.2.12 FlexibilityMany museums and art galleries change their displays regularly or house temporary exhibitions.Different displays or exhibitions require different lighting so it is essential to have flexibility.Flexibility of positioning can be provided by using a track system to power spotlights. Flexibilityin the amount of light can be provided by having different elements of the lighting on differentdimming circuits. Flexibility in light distribution can be achieved by using spotlights withdifferent beam widths.

13.3 Lighting approaches for museums and art galleries

13.3.1 Wall mounted displaysLighting paintings hung on a wall requires care if veiling reflections and shadows are to beavoided. Uniform lighting over the whole wall can be achieved using wall washing luminaires.Uniform lighting over individual pictures can be achieved using spotlights. In this case, somespill light around each picture will soften the effect and illuminate any label. Where a painting ishung so that it can be viewed by a standing observer looking straight ahead, spotlights aimed sothat the centre of the beam is on the centre of the painting and 30 degrees from the downwardvertical usually produce satisfactory conditions. Where paintings are double hung, i.e. one abovethe other, the upper painting should be tilted down to minimise veiling reflections.

13.3.2 Three-dimensional displaysFreestanding, three-dimensional objects need to be lit from several different directions. The usual approach is key-, fill-, background- and up-lighting (see Section 12.4). Back lightingdetermines the context in which the object will appear and sets the levels that will be requiredfor key-, fill- and up-lighting to be noticeable.

Key-lighting consists of a narrow beam aimed at the most important features of the object. This will create shadows and highlights on the object. Highlights reveal the nature of surfaces.Shadows reveal form and texture. However, excessive highlights can be glare sources and strongshadows can hide detail. Key-light is offset by fill-light and up-light, diffuse lighting that softensshadows and diminishes glare. By balancing key-, fill- and up-light in direction and amountrelative to the back-light, a wide range of appearances can be created.


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The other problem with three-dimensional displays is avoiding glare to the viewer, not fromthe object but direct from the luminaires. When the object is at eye level or lower and is litfrom all sides with the beam angles less than 30 degrees from the downward vertical glareshould not occur. Where the object is large and requires the viewer to look upwards, glare is apossibility. This can be dealt with by restricting the directions from which the object is viewed,or using narrower beams for the key-light so that all the light is within the display or lightingfrom below as long as appearance is not distorted.

13.3.3 Showcase lightingGlazed showcases are used for displaying rare, valuable and delicate objects while protectingthem from damage and theft. Showcases can be small or large; can be viewed from all sides orfrom a limited number of sides; and can be lit from outside the case or from inside. Theproblems of showcase lighting are reflections from the glazing, shadows produced by viewersand heat build up in the case.

Reflections from the glazing and shadows caused by viewers are mainly problems with externallighting, particularly when the showcase has a low reflectance (dark) lining. Reflections can bedealt with by tilting or curving the glazing so that a dark surface is reflected or by creating aluminance ratio of 10:1 or greater between the interior and exterior or the showcase. Shadowshave to be dealt with by using multiple light sources.

Using carefully aimed interior lighting for the showcase will eliminate problems withreflections from the glazing. Whether shadows occur around and on the objects in the showcasewill depend on how the objects are lit and the reflectance of the surfaces in the case. The moredirectional the lighting and the lower the reflectance of the interior, the more likely it is thatshadows will occur around the object.

One form of interior lighting is the light-box on top of the showcase. This can provide softdiffuse light using fluorescent lamps or directional lighting using adjustable spotlights. Light-boxes need to be ventilated to prevent heat build-up and have easy access to the lamps formaintenance. There should be a glass or plastic barrier between any fluorescent lamps in thelight-box and the case interior to filter out ultra-violet and infrared radiation. For some tall ornarrow showcases, the top lighting will need to be supplemented by lighting from the sides,back or bottom to provide good modelling of objects on the lower shelves and to alleviateshadows. Another form of interior lighting is small spotlights mounted in the corners of theshowcase. Fibre-optic lighting has distinct advantages for such an approach. The light sourcecan be mounted outside the showcase thereby avoiding heat build-up and the fibres can befiltered to eliminate ultra-violet and infrared radiation. Further, the fibres can be fitted withdifferent light distribution devices and can be moved around the showcase as required.


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Chapter 14: Lighting for hospitals

14.1 Functions of lighting in hospitals

The lighting of hospitals has two main functions. The obvious and most important function is tomeet the task requirements in each area of the hospital. Some of the tasks to be carried out willrequire exacting levels of visual performance. Indeed, the safety of the patients may depend onthe level of visual performance achieved. The second and equally important function is to createan environment that is visually satisfying, wholly appropriate and ‘emotionally compatible.’Lighting can influence human emotions and feelings of well-being. Good lighting will also helppromote an air of quality and competence within the hospital.

Extensive guidance on the lighting of hospitals is given in SLL Lighting Guide 2: Hospitals andhealth care facilities and other publications (Dalke et al., 2003).


14.2.1 DaylightThe provision of some daylight and a view out is much appreciated by patients, so daylightingand access to windows should always be considered when designing the lighting of hospitals.However, care is necessary to limit sun penetration so that thermal and visual discomfort do notoccur. Further, the amount of light coming through the windows at night needs to be restrictedif sleep is to be undisturbed. This means that windows should be fitted with adjustable blinds.Where daylight makes a major contribution to the lighting of the space, the electric lightingshould be fitted with an automatic switching or dimming system so that energy waste is avoided.

14.2.2 Lines of sightHospitals differ from many places in that some common lines of sight are unusual. For patientsin hospitals, common lines of sight are towards the ceiling and the upper parts of the oppositewalls. Such common lines of sight mean that special care is necessary to avoid glare to patientswhile still providing good visibility to doctors and nurses.

14.2.3 Colour rendering requirementsSkin colour, eye colour and the colour of tissue and fluids can be important guides to diagnosisand treatment. Therefore, there are strict colour rendering requirements placed on the lightsources used in the clinical areas of hospitals. Clinical areas include ward units, consulting roomsand operating departments. Ward units include bedded areas, ward corridors, nurses’ stations andtreatment rooms. All fluorescent lamps within these areas should have a CIE general colourrendering index of at least 80.

In specialist areas such as those used for examination or treatment, a minimum CIE generalcolour rendering index of 90 is recommended. However, these areas generally do not require thegeneral illumination to be provided by such lamps, only the immediate task area. This task arealighting will usually be provided by dedicated fixed or mobile examination lamps.

It is essential that light sources with different colour rendering or colour temperaturecharacteristics are not used in the same area. If the bed head reading lights are intended tosupplement the general illumination for the purposes of patient treatment, then the light sourcesused in the reading lights should have a CIE general colour rendering index of at least 90.


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14.2.4 Observation without disturbance to sleepLighting in hospital wards suffers from a conflict of interest at night. The patients are trying tosleep, while the staff need to be able to see the patients, move around safely and do detailedwork at the nurses’ station. The differences between the visual requirements of these activitiesmeans that ward lighting needs to be flexible. Crude flexibility can be achieved using switching.Fine flexibility can be designed using dimming.

14.2.5 Emergency lightingEmergency lighting is required for the movement of patients, staff and visitors to a safe locationin an emergency. Some of the people in a hospital will almost certainly be physicallyincapacitated and/or could be mentally impaired. Because of the likely condition of patients,hospitals do not normally fully evacuate in an emergency. Patients are generally moved by aprocess called progressive horizontal evacuation from high risk areas to low risk areas while theemergency is brought under control. The emergency lighting should be sufficient to allow easyprogressive horizontal evacuation, particularly in those areas where elderly patients may bepresent. Emergency lighting should be designed to meet the requirements of BS 5266. Designguidance can also be obtained from the SLL Lighting Guide 12: Emergency lighting design guideand from Chapter 8 of this Handbook.

For hospitals, the minimum illuminance on the centre line of a 2 meter wide escape routeshould be 1 lx. A minimum illuminance of 0.5 lx should be provided on all non-designatedescape route areas requiring emergency lighting. Fire muster points and dedicated refuge areasmust be given special consideration to ensure they are illuminated to a minimum of 5 lx and arevisible or stand out from the general surrounding area. Illuminated signs on the movement andescape routes should comply fully with BS 5499: Parts 1 and 4 and BS EN 50172.

Standby lighting will be required in certain parts of the hospital to enable essential activities tobe carried out in the event of a supply interruption. Hospitals normally work to two standardsof illuminance for standby lighting. In critical areas, such as operating theatres, delivery roomsand high dependency units, the illuminance provided by the standby lighting should equal, ornearly equal 90 percent of the normal mains illuminance. Other non-critical but importantareas will require standby lighting to a reduced illuminance, generally to 50 percent of thenormal mains level.

Where standby lighting is provided by a generator, there will always be a break in the continuityof supply as the engine runs-up so a battery back-up with a minimum of 3 hours capacity topower the lamp(s) should be provided to cover the start-up period and to cater for thepossibility that the generator fails to start.

14.2.6 Luminaire safetyAll luminaires should comply with the relevant part of BS EN 60598. They should all carry aCE mark with the manufacturer’s declaration of conformity to all directives designated underthe harmonised European Standards and certified to be in full compliance with the EMCDirective. In addition all luminaires intended for use within clinical areas of healthcarebuildings should specifically comply with the requirements of BS EN 60598-2-25.

Electrical safety should be considered a top priority for all electrical apparatus used withinhospitals, especially in bed-head luminaires that are accessible to patients. Such luminairesshould be either be of Class II construction or supplied from a safe extra-low voltage supply(SELV), as defined in BS EN 60598: Part I: Section 1.2.


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lsThe construction should be robust and the luminaires should be capable of being securelymounted. Provision should be made for easy cleaning of the interior of enclosed luminaireswithout the risk of electrical shock.

Hand-held switches at mains voltage can be dangerous to patients so an extra-low voltage relay-actuated switch, at a maximum of 24 volts, should be incorporated into any nurse-call apparatus.Electrical connections should be accessible only with the use of tools.

It is also worth noting that any recessed emergency luminaires used on an escape route will haveto retain the fire integrity and the rate of fire spread of the surrounding ceiling system. In practicethis means that any attachment used will have to withstand the 850 ˚C glow wire test and bemanufactured from a self-extinguishing material such as polycarbonate or a TPa based polymer.

14.2.7 CleanlinessIt is possible for airborne dust particles as small as 0.5 µm to transport harmful bacteria.Luminaires in common with other items of equipment can cause the transfer of infection bycontact with the dust particles they may harbour. Therefore, luminaires for use in hospitalsshould have the minimum area of horizontal or near horizontal surfaces on which dust may settleand such dust should be easily removable by simple cleaning methods. In high risk areas it isadvisable to use luminaires with no horizontal faces, only downward and vertical faces. It is alsoadvisable to use theatre luminaires that have glass diffusers since glass cannot be penetrated bybacteria and is unaffected by sterilising materials and UV radiation. A further measure inpreventing the transmission of infections is to ensure that any space requiring ingress protectionbetween the void and room (especially theatre luminaires), uses a luminaire that has integralmechanical measures to ensure the seal between the ceiling and the luminaire frame and does notrely on the luminaire being manually held while it is fixed into place.

14.2.8 Electro-magnetic compatibility (EMC)Many items of electrical equipment installed in hospitals can cause interference, either byradiation or by transients through the mains voltage supply. The prime nuisance factor fromfluorescent luminaires is from radio interference. Suppressors, if fitted to the ballasts within theluminaires, should reduce the interference.

The use of high frequency electronic control gear within the patient environment requires carefulconsideration with regard to EMC emissions and immunity. The testing and certification of aballast by a manufacturer as an independent component is not sufficient to ensure that its usewithin another housing or product will meet the overall technical requirements. Tests need to beperformed by manufacturers on the complete assembly, as it would be installed. BS EN 60601defines the EMC test requirements for electrical medical equipment within the patientenvironment. The EMC elements of ISO 11197 should be observed for bed head servicetrunking systems that include lighting components.

14.3 Approaches for the lighting of different areas in hospitals

The areas considered here are those most likely to be experienced by those visiting a hospital aspatients. Hospitals contain many other areas. Details of the lighting required for all areas ofhospitals are given in SLL Lighting Guide 2: Hospital and health care buildings.


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14.3.1 Entrance halls, waiting areas and lift hallsIn the main entrance of a hospital visitors will look for signage to direct them towards theirdestination. The lighting should be designed in conjunction with interior materials and finishes toclarify transit routes and points of arrival. A change of type, height or orientation of the luminairescan highlight the focal point of activity such as reception, waiting areas and lifts (Figure 14.1).This approach to design will also provide brightness variations that contribute to the pleasantnessof the interior. A maintained illuminance of 200 lx on the floor is recommended.

Figure 14.1A hospital entrance area

14.3.2 Reception and enquiry desksMaintained illuminances of 300 lx on the floor of the reception area and 500 lx on the task areasare recommended. The overall impression should be a welcoming one that avoids harshcontrasts (Figure 14.2). It is important to consider the vertical as well as the horizontalillumination, so that people’s faces within the reception areas are properly lit as this will providegood facial modelling and help with the process of lip reading.

Figure 14.2A hospital reception area


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14.3.3 Hospital streets and general corridorsHospital streets form the major links between clinical departments and may include publicwaiting areas. They have a relatively high traffic density and can be in excess of 6 m wide .General corridors can vary from the minor, linking one or two offices, to the major, linkingdifferent departments (Figure 14.3). For both areas, a maintained illuminance of 200 lx on thefloor is recommended. A lower maintained illuminance of 50 lx is recommended for use atnight, the lower illuminance being achieved by either selective switching or, preferably, bydimming. If selective switching is used then care should be taken to maintain an illuminanceuniformity (minimum/average) of at least 0.2. This will provide the staff with a morecomfortable level for moving to and from dark wards and will also avoid the patients beingdisturbed by the glow of bright lights from the corridor. Low glare luminaires should be used,positioned to avoid alternating brightness patterns being viewed by trolley-borne patients.

Figure 14.3Hospital corridor

14.3.4 Changing rooms, cubicles, toilets, bath, wash and shower roomsA maintained illuminance in the range of 100 to 150 lx on the floor is recommended. Thelower illuminance is considered adequate for small, enclosed cubicles. In the interest ofcleanliness, these areas should be lit to minimise shadows and no areas should have to relysolely on reflected light. Bathrooms and shower rooms are humid therefore special attention isrequired in the selection and the location of the luminaires. In changing areas, the luminairesshould be sited between clothes racks or lockers to provide adequate light into the lockers. Thepositions of wall-mounted mirrors and of the general lighting should be chosen to avoidtroublesome reflections.

14.3.5 WardsThe lighting of wards must satisfy the requirements of both the patients and the nursing staffduring the day, evening and night. In bed spaces, it is now common practice for the light levelsrequired to administer medical or general patient care to be provided without the use of aseparate portable luminaire. Lighting of bed spaces should be individually switched toencourage energy saving when the bed space is unoccupied. Lighting of the central ward areashould be provided so as to enable safe circulation and general cleaning procedures to be carriedout. Most importantly the lighting of the whole ward should aid in the provision of a generalpleasant and amenable ambience.


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For nursing care to be performed efficiently the maintained illuminance over the general area ofthe bed should be at least 300 lx with a uniformity (minimum/average) of 0.5 or better. A combination of general and task lighting may be used. The maintained illuminance in thecentral space between the beds should be not less than an average of 100 lx at floor level. Thislevel will be sufficient for the general activities of ambulant and recumbent patients withoutcausing disturbance to other patients in the room who may want to rest.

It is common practice that when patients are being attended to by nursing or medical staff, theirbed curtains will be pulled around to provide an element of privacy. When the bed curtains arepulled around, the average illuminance within the curtained area for both the general level andthe nursing care level must not be reduced by more than 25 percent when compared to theunscreened bedded area. A minimum acceptable mean illuminance of 75 lx for the general wardlighting should be maintained outside the bedded area when all the bed curtains within theward are drawn around simultaneously.

The lighting of wards can be done in several different ways. Ceiling mounted ward luminairesare usually required but these can be supplemented with bed lighting consisting of compactfluorescent lamps in ceiling-recessed luminaires positioned centrally over the bed area or linearfluorescent luminaires mounted on top of a strengthened curtain rail between beds to provideuplighting. This latter approach will not be appropriate where the distance between the curtainrail and the ceiling is less than 1 m and/or where the ceiling height is more than 3 m (Figure14.4). Another possibility is to use luminaires that are integral within a wall-mounted bed-headservices trunking system that also provides piped medical gas and cabled services. The optimummounting height for such integrated luminaires is 1.8 m. Any luminaire mounted below 1.8 mwill need careful light control if glare to patients and staff is to be avoided.

Ceiling mounted ward luminaires can be suspended, surface mounted or recessed. The minimumceiling height required for suspended luminaires to be considered is 3.5 meters. This will ensurethat adequate clearance is still possible for the use of mobile apparatus at the bedside. Themounting height above the floor should not be less than 2.7 m nor greater than 3.5 m. If the luminaire has an upward light component the suspension length should be between 700 mmand 1000 mm to achieve a satisfactory spread of light across the ceiling. For surface-mountedluminaires, the ceiling height may be 2.7 m or less. It is usually convenient to mount single-lampfluorescent luminaires to coincide with the bed spaces. Twin-lamp luminaires may also be used,usually spaced at one and a half times the bed spacing.

Figure 14.4Ward and bedhead lighting


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lsHowever, the illuminance in the circulation space could be less uniform and somewhat higherthan the recommended value when using this method. In areas with ceiling heights between 2.4 m and 2.7 m, it is possible to provide the recommended illuminance at the bed head byusing surface mounted luminaires alone.

Recessed and semi-recessed luminaires may be used in ceilings between 2.4 m and 3 m high.Luminaire spacing should generally be as described for surface mounted luminaires.

It is also possible to illuminate wards using wall mounted luminaires that combine an upwardand downward component. This method has numerous advantages. The downward componentallows patients to do visually demanding tasks like reading or jigsaw puzzles. The upwardcomponent provides non-glaring, soft illumination to the room allowing the patients to relax.When combined, the upward and downward components can provide the higher level ofillumination required for examination or nursing care.

Ward lighting should not cause glare to recumbent and ambulatory patients. Ceiling or wallmounted luminaires should be assessed for their average luminance value at elevation anglesbetween and including angles (a) and (b) in Figures 14.5, 14.6. and 14.7. Ceiling mounted,surface luminaires should not exceed 1500 cd/m2 for all angles of azimuth. For all ceilingrecessed or semi-recessed luminaires the value should be reduced to 1000 cd/m2. Wall mountedluminaires should be assessed for their average luminance value which should not exceed 700 cd/m2 for all angles of azimuth, between and including angles (a) and (b), as defined inFigure 14.7 where:

(h1) is the minimum height of the mattress surface plus 200 mm

(h2) is the maximum height of the mattress surface plus 600 mm

(h3) is the height above floor level to the centre of the luminaire

(d1) is the distance from the wall to the front edge of the pillow

(d2) is the distance from the wall to front face of bed head

(d3) is the distance from the wall to the luminaire centre.

The average luminance value of 1500 cd/m2 (1000 cd/m2 for recessed or semi-recessedluminaires), is defined as the luminous intensity measured at each 5˚ angle between andincluding angles (a) and (b) divided by the sum of all the orthogonally projected luminous areasat each of the elevation angles. This average applies at all angles of azimuth. The average valueof 700 cd/m2 for wall luminaires should not be exceeded anywhere between and includingangles (a) and (b) for all angles of azimuth. The designer should use the measurement valuesrelating to the actual or specific areas in question. However, in the absence of specificdimensional data for h1, h2, h3, d1, d2 and d3 the following values should apply;

h1 = 850 mm

h2 = 1450 mm

h3= 2.7 m ceiling mounted, 2.0 m rail mounted, 1.8 m wall mounted

d1 = 900 mm

d2 = 450 mm

d3 = 4.0 m ceiling mounte, 5.0 m rail mounted, 8.0 m wall mounted.


d1d2

h1

h2

d3a

b

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The average luminance valueshould not to exceed 700 cd/m2

between and including angle (a)and (b) for all angles of azimuth

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Figure 14.5 Elevation angles for ceiling mounted luminaires

The average luminance valuebetween and including angles (a) and (b) not to exceed 1500 cd/m2 for all angles of azimuth

d3

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Figure 14.6 Elevation angles for bed head rail mounted luminaires

The average luminance valueshould not to exceed 700 cd/m2

between and including angle (a)and (b) for all angles of azimuth

d3

d1

h1

h2

d2

a

b

0˚

b = 120˚ for luminairesmounted below 1.8 m

b = 90˚ for luminaires mountedat 1.8 m but below 2.0 m

b = actual measured anglefor luminaires mounted ator above 2.0 m

Figure 14.7 Elevation angles for wall mounted luminaires

h3


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For wall-mounted luminaires fixed at ≥ 2.0 m angle b shall be the actual measured value. Atmounting heights of ≥ 1.8 m but less than 2.0 m from finished floor level, angle b shall alwaysbe 90 degrees. For mounting heights below 1.8 m angle b shall always be 120 degrees. Themaximum luminance must not exceed 700 cd/m2 at any angle of azimuth between andincluding, the angles of elevation detailed in Figure 14.7 above.

Luminaires must not cause excessive luminance spots (bright patches), on the room surfaceswhen viewed by the patients. The average luminance of all the major reflecting surfaces shouldnot exceed 600 cd/m2 and the maximum measured spot level should not exceed 1500 cd/m2. Inaddition there should be no sudden change in the values of luminance on any of the majorreflecting surfaces, i.e. they should change gradually.

14.3.6 Reading lightingWhen reading, most people will rest with their head or back against the pillows. A reading lightshould provide an average illuminance of 300 lx over a horizontal area of 1m x 1m centred atthe bed-head and directed towards the bottom of the bed at 1.0 m above floor level, after takinginto account the shielding effect produced by the patient’s head and shoulders. The readinglight switch should be conveniently positioned within reach of the patient. Suitable readinglights, especially if they are articulated, may also be used for general nursing activities at thebeds. All reading lights should be cool to touch and easy to clean. Ideally, wall-mounted fixedbed-head type reading lights should be installed at a mounting height of 1.8 m but can bemounted below 1.8 m provided care is taken to control glare and shadows. Articulated wall-mounted reading lights and ceiling-mounted reading lights can also be used.

14.3.7 Night lightingNight lighting needs to fulfill three functions: to provide enough light for the safe movementaround the ward, to allow the nursing staff to see facial features and a patient’s generalcondition, and to allow patients to sleep. The average maintained illuminance for the centralward circulation space should be 5 lx on a 0.85 m high horizontal working plane, with amaximum illuminance measured on the pillow of 0.5 lx. To avoid disturbing glare, theluminance of any luminaire left on during the night within the ward should not exceed 30 cd/m2 at an angle of 35˚ and more from the downward vertical at all angles of azimuth.

In addition, any luminaire positioned at the bed head or within the bedded area defined by thescreening curtains should not exceed 30 cd/m2 at an angle of 20˚ and more from the downwardvertical at all angles of azimuth.

Moving shadows cast by car headlamps, trees or from nearby road lighting can be particularlydisturbing to patients, it is recommended therefore that blinds or curtains be drawn over thewindows at night where external sources are considered to be an issue.

14.3.8 Night observation lighting (watch lighting)Watch lighting may be required for the observation of a particular patient after the generallighting has been switched off. It should avoid any visual disturbance to other patients so it isunlikely that the general use of a patient’s reading light, which has not been designed for thispurpose, will be successful. An illuminance of 15–20 lx at the bed head is considered adequatefor this task, provided the night lighting is of the recommended level.


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14.3.9 Clinical areas and operating departmentsClinical areas and operating departments are locations where surgical, clinical or medicalprocedures are carried out. The main function of lighting in such areas is to provide sufficientlight for the critical examination of patients, for carrying out operating procedures and for theuse of life support apparatus. It is essential that the general lighting should have a CIE generalcolour rendering index of 90 or more and should provide an even distribution of illuminancethroughout the department.

Ceilings and walls should have a semi-gloss or eggshell finish. The walls should not producereflected images of the luminaires, especially where they might occur at the eye-height ofoperating theatre staff. The ceiling reflectance should be 0.7 to 0.9 which can be achieved by theuse of off-white or a pale shade, other than blue or green. This will assist in controlling theluminance contrast between the ceiling and the general lighting luminaires. The walls shouldhave a tinted finish, rather than white, with a reflectance of 0.5 to 0.8. The floor should have alight-tone finish with a reflectance of at least 0.3 to maintain an adequate inter-reflected lightcomponent, especially within the actual operating theatre.

All luminaires used within a theatre complex should have ingress protection of at least IP 54. In addition all luminaires must be constructed to allow for easy cleaning.

14.3.10 Operating theatresEuropean standard BS EN 60601-2-41: 2000 provides detailed information on the requirementsof ‘luminaires for diagnosis’, ‘minor (treatment) surgical luminaires’ and ‘major and systemsurgical luminaires.’

The illuminance in the surgical field will be determined by the type of surgical procedure, thedepth of the body cavity to be illuminated and the angle of illumination. Consequentlydifferent surgical procedures will require operating luminaires of varying luminous intensitiesand illuminated field sizes. In a large operating theatre suite each theatre may be equipped withan operating luminaire specifically suited to the type of surgery to be undertaken in eachtheatre. In smaller suites where various types of surgical procedures will be undertaken in thesame theatre, it will be necessary to select an operating luminaire that will provide the best all-round solution (Figure 14.8).

Figure 14.8Operating theatre luminaires


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lsThe maintained illuminance for general lighting of operating theatres is 1000 lx. This is usuallyadequate for performance of ancillary tasks by theatre staff. To minimise the possibility ofbacterial transmission the general theatre luminaires should have ingress protection of IP ≥ 65/54; that is IP65 void-to-room with the front frame fixed on and IP54 when the frame is off for lamp replacement.

The general lighting is required to provide both horizontal and vertical components ofilluminance, vertical being required for good visibility of swab count racks, wall-mountedequipment, life support equipment etc., the surfaces of which should not be glossy.

For ophthalmic, ear, nose and throat (ENT), and micro-surgery, much lower levels of generalilluminance will be required. A value of between 10 to 50 lx is recommended. Dimming willprovide the flexibility that is often required in theatres to permit multi-functional use

Surface mounted or, in some instances, wall mounted luminaires may be required wheretheatre ceilings are not suitable for recessed luminaires. If wall mounted luminaires are usedcare should taken to ensure that the minimum horizontal light requirement is achieved withoutglare to theatre staff.

Practice has shown that glare should not be a problem in the comparatively small areas ofmodern operating theatres provided that the recommended illuminances, colours andreflectances are used and linear recessed or surface fluorescent luminaires having a downwardlight output ratio of approximately 0.6 are specified.

Failure of the lighting during an operation may have serious consequences and it is essential toprovide sufficient and reliable standby lighting. Instantaneous change-over to the standbysupply is required for the major surgical luminaire or surgical luminaire system.


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Chapter 15: Quasi-domestic lighting

15.1 Functions of quasi-domestic lighting

Quasi-domestic lighting is found in places that seek to appear as private residences but whichare, in fact, communal dwellings. Examples of such locations range from halls of residence forstudents through care homes for the elderly to hotels. The lighting in such locations has twomain functions. The first is to enable the residents to see what they want to see, withoutdiscomfort. The second is to create a visual environment that is attractive and interesting or atleast one that avoids looking ‘institutional.’ The balance between these two functions varieswithin and between each application. For example, in a hotel, the room lighting is dominatedby the need to create an attractive and interesting visual environment although bed headlighting will also be designed to ensure that reading is easy. In contrast, in a home for theelderly, greater importance is attached to ensuring that the residents can see what they need tosee, although the need for a non-institutional appearance should not be neglected.


15.2.1 Occupants’ capabilitiesDifferent communal dwellings may contain people with very different visual capabilities. Theoccupants of halls of residence at a university are mainly likely to be young with good visualsystems. Conversely, the occupants of homes for the elderly will almost certainly be old andmany may have some form of visual disability (see Section 2.8.2). Guidance on lighting forpeople with low vision is given in the SLL Factfile No 10: Providing visibility for an ageingworkforce and elsewhere (LRC, 2001d; Goodman, 2008). A realistic assessment of the visualcapabilities of the occupants and what it is they need to see is necessary before starting to designthe lighting.

15.2.2 DaylightAccess to daylight and a view out is strongly desired by most people. Therefore, daylighting andaccess to windows should always be considered when designing quasi-domestic lighting. Themain limitation on this is the desire for privacy in some rooms such as bedrooms andbathrooms, although, even here, there is a desire for daylight some of the time. Privacy andsome control of discomfort due to solar glare can be ensured by fitting windows with curtainsor blinds.

15.2.3 Light source colour propertiesThe appearance of the room décor is important in quasi-domestic lighting. The room décormay have been chosen with care to create the required ambience but the effect will be ruined ifthe appearance of the décor changes between daytime, when the room is daylit, and after dark,when it will be lit with electric light sources. Similarly considerations apply to skin colour. Skincolour is widely used as an indicator of health. Lighting which distorts skin tones will not beacceptable. Such considerations rarely cause a problem with incandescent light sources but theycan when inappropriately chosen fluorescent light sources, such as those with a high correlatedcolour temperature (see Section 1.4.3), are used. To avoid such complications, any light sourceused in quasi-domestic dwellings should have a CIE general colour rendering index of 80 orgreater and a correlated colour temperature of 3500 K or less. This is particularly important inbathrooms and bedrooms.


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15.2.4 Energy efficiencyPart L of the Building Regulations applies to quasi-domestic dwellings (SLL Factfile No.9,2006). This imposes limits on the type and amount of lighting equipment that can bepermanently installed although there is a useful loophole in that plug loads, such as table lamps,are unrestricted. Further, there are proposals to restrict the supply of conventional incandescentlamps over the next few years, the intention being to increase the use of light sources withhigher luminous efficacies, such as tungsten halogen and compact fluorescent. When in theform of recessed downlights, tungsten halogen can pose a fire hazard if not properly installed,as discussed below, and compact fluorescents may not conform to the advice about light sourcecolour properties given above.

15.2.5 SafetyThere are three particular aspects of safety that should concern the designer of quasi-domesticlighting. The first involves the use of recessed tungsten halogen downlights. These are anincreasingly popular approach to domestic lighting. The problem is that these lamps get veryhot with the result that flammable material should be kept well away from them, a fact that issometimes forgotten once they have been inserted into a hole in the ceiling. Where downlightsare installed in a ceiling there is concern about the preservation of the fire barrier representedby the ceiling and the transfer of sound between rooms. The easiest way to overcome theseproblems is to use downlights with built-in fire and acoustic protection. An alternativeapproach to minimising the fire hazard is to install covers over the back of the downlights toensure each downlight is separated from other materials.

The second applies to bathrooms and shower rooms where there are restrictions on the type ofluminaire that can be installed in different locations (Table 15.1). These restrictions aredesigned to minimise the likelihood that someone will get an electric shock while in contactwith water. Washbasins are not covered by the regulations but are usually treated as zone 2.

Table 15.1 Zones identified for luminaires in bathrooms and shower rooms by the 17th

edition of the IEE Wiring Regulations

Zones

0

1

2

Location and limitation

Any luminaire installed inside a bath or shower tray which can hold watershould be low voltage (maximum 12 V) and have an IP rating of IPX7

Any luminaire installed in the volume above a bath or shower tray to aheight of 2.25 m from the bottom of the bath or shower tray or for ahorizontal distance of 1.2 m from the center of a shower outlet and

vertically up to the height of the shower outlet or 2.25 m, whichever is thehigher, should have a minimum IP rating of IPX4 or be of safety extra-low

voltage with the transformer beyond zone 2

Any luminaire installed outside zones 0 and 1 but inside the volumespecified by a boundary set 0.60 m horizontally outside the perimeter of the

bath or shower tray and 2.25 m vertically above the floor, should have aminimum IP rating of at least IPX4 or be safety extra-low voltage with the

transformer located beyond zone 2

The third requires the installation of an emergency lighting system (see Chapter 8). Emergencylighting is required for the safe egress of residents in the event of an emergency. In some quasi-domestic dwellings, such as care homes for the elderly, some of the residents will almost certainlybe physically incapacitated and/or could be mentally impaired.


Maintainedilluminance (lx)

200

300

100

100

150

100

150

150

150

50

150

500

300

Plane of measurement

Floor

Working surface

Floor

Treads

Desk

Wash basin

Worktops and cooker

Worktops and washing machines

Floor

Floor

Tables

Table

Table

Location

Entrance

Reception desk

Corridors

Stairs

Study bedroom

Study bedroom

Small kitchen

Utility room

Lounges

TV lounge

Dining hall

Games rooms – billiards or snooker

Games rooms – Table tennis216

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For such situations, it would be better to follow the approach used in hospitals (see Chapter 14).General design guidance can also be obtained from the SLL Lighting Guide 12: Emergency lightingdesign guide.

15.2.6 SecurityOne feature that distinguishes quasi-domestic buildings from private residences is that strangersmay be encountered inside the building as they make their way to the room of the person theywant to meet. This part private/part public nature of the building means that security is a specificconcern, a concern that may be addressed by CCTV surveillance (see Section 18.2.5). For hallways, stairways and other communal areas, lighting that enables recognition of faces isessential to determine who belongs in the space and who doesn’t; who is perceived as safe andwho may present a danger.


The lighting recommendations for quasi-domestic buildings are very simple. This is because thelighting is usually designed to fit around the furnishings, so concern with illuminance uniformityis often inappropriate. Where illuminance uniformity is a consideration, a minimum illuminanceuniformity (minimum/average) of 0.8 is recommended. Further, many of the spaces are small so glare is not a problem because the luminaires are usually far away from the common lines ofsight. Where glare is of concern it can usually be dealt with by ensuring the no part of theluminaire has a luminance greater than 300 cd/m2 when seen from common directions of view. As for the light source colour properties, these have been dealt with above. As a result of theseconsiderations, the quantitative lighting recommendations are restricted to the minimummaintained illuminances that should be provided at particular locations (Table 15.2). Theserecommendations are applicable to quasi-domestic buildings occupied by young people. Forquasi-domestic buildings where elderly people predominate, see the recommendations of theThomas Pocklington Trust (Goodman, 2008).

Table 15.2 Maintained illuminances recommended for different parts of some quasi-domestic buildings


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15.4 Approaches to lighting quasi-domestic buildings

15.4.1 EntrancesThe first requirement for anyone approaching a building is the ability to identify the entrance.This can be ensured by lighting the entrance so that the doors and any sign identifying thebuilding can be seen from a distance. The second is to move safely up to the entrance. For thispurpose, the illuminance on the ground should be increased close to the entrance to the samelevel as that inside so as to provide a smooth transition zone between the exterior and the interior.This is particularly important for buildings where the elderly may be found because it allows moretime for visual adaptation to occur. Where there are steps on the approach to the building, theseshould be lit after dark using column mounted urban area luminaires or bollards. Floodlightsmounted low on the building should not be used as they tend to produce severe glare to thoseapproaching the building.

At the entrance, lighting should be provided both outside and inside. The purpose of such lightingis to make whoever is outside visible to the person opening the door and vice versa. For this tohappen, there has to be a window or wide-angle viewer fitted in the door. As for the lighting,downlights mounted above the door should be avoided as they create shadows on the face thatmake identification difficult. A better approach is to use low luminance diffuse lighting placed onboth sides of the door.

The entrance hall gives the visitor a first impression of the building and provides importantinformation about where to go. This information may be gained from display boards or from areception desk. Display boards should have their own dedicated lighting. Reception desks shouldbe lit to a higher illuminance than the rest of the space and the lighting should be designed toprovide good vertical illuminances so that the faces of the receptionist and the visitor are clear.

15.4.2 Corridors and stairs In corridors, the aim of the lighting should be to light the walls as well as the floor. If linear lightsources are used, the long axis should be oriented along the corridor. If the corridor is narrow, analternative approach is to use cove lighting along one side of the corridor. The illuminanceprovided in a corridor should be at least 100 lx in daytime where there is no significant daylightcontribution. After dark, but when people are still about, this can be reduced to 50 lx. Late atnight, when most people are asleep a minimum of 5 lx is required provided there is some meansto restore the illuminance to 50 lx on demand. Stairs should be lit so that there is a flow of lightfrom top to bottom. This means that the treads will be illuminated but the risers will not. Figure 15.1 suggests what locations should and should not be used for luminaires. In addition to lighting, contrasting markings on the nosing of each tread are a useful safety feature.

A+B+

C+

D+

Figure 15.1Staircase lighting: position A is recommended, B and C are to be avoided, and D can be used forwall-mounted luminaires on very long staircases


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15.4.3 Study bedrooms Study bedrooms require lighting that is flexible to enable the residents to have some individualcontrol over what is essentially the only private space available to them. Sufficient flexibility canbe provided by using adjustable local lighting on the desk and dimming of the main room light(Figure 15.2). The main room light should provide diffuse light of at least 100 lx at desk height.This will be easier to achieve if the room surfaces are of medium to high reflectance. Lightingof the en-suite facilities has to conform to the requirements for bathrooms and should becentred on the washbasin and mirror.

Figure 15.2Lighting of studybedrooms for flexibility

15.4.4 Kitchens and utility roomsIn many quasi-domestic buildings, kitchens and utility rooms are communal facilities. Thelighting of these areas is utilitarian and should provide an average illuminance of 150 lx at thecooker/washing machine level. The luminaires used should be capable of withstanding watersplashes (IP44). Light sources used in kitchens should have good colour rendering (CRI > 80).

Bare light sources should not be used. Rather, enclosed luminaires that are easily cleaned andwhich ensure that if a light source brakes pieces of glass do not fall into the food are preferred.Luminaires with a diffuse light distribution and medium to high reflectance surfaces arerequired if people using the cooker or washing machine are not to be in their own shadow(Figure 15.3). As kitchens and utilities may be left unoccupied for some time, occupancysensors should be fitted to avoid wasting energy.

Figure 15.3Lighting of kitchensdesigned to avoid shadows


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15.4.5 LoungesLounges are social areas where people may gather to talk, read or watch television. The lightingshould contribute to a relaxing atmosphere. This can be achieved by providing sufficient lightfor reading in some areas, low light levels in others, taking care to avoid reflections of light inthe TV screen, and by providing some emphasis on important features of the space, such aspictures. Illuminance uniformity is not important for lounges but the integration of the lightingwith the architecture is. Flexibility through preset ‘scenes’ provided by a preprogrammedcontrol system is an attractive option.

15.4.6 Dining hallsThe dining hall is where residents gather for meals. The ambience can vary from that of anexpensive restaurant to that of a youth hostel, although the latter is more common. Wheremeals are collected by the residents from a servery, on trays, the usual approach is to provideuniform lighting over the tables, although some interest may be created by lighting particularfeatures of the dinning hall. Localised lighting is provided over the servery itself and infrareddownlights are often used to keep the food warm.

15.4.7 Games roomGames rooms may require special lighting depending on the games played and the standard atwhich they are played. Extensive advice is given in SLL Lighting Guide 4: Sports lighting.However, for games played primarily for amusement, uniform lighting producing a minimummaintained illuminance of 200 lx at floor level is sufficient. If fluorescent lighting is used, highfrequency electronic control gear should be used. Further, the décor should be plain,particularly where high speed movement is involved, e.g. table tennis.


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Chapter 16: Road lighting

16.1 Road classification

Road lighting is divided into three classes; traffic routes where the needs of the driver aredominant, subsidiary roads where the lighting is primarily intended for the pedestrian and thecyclist, and urban centres, where the lighting is designed to do what can be done for public safetyand security, while also providing an attractive nighttime environment. The photometricrecommendations for all types of road lighting in the UK are given in BS EN 13201: Part 2.Advice on the implementation of these recommendations is given in BS 5489-1 together withAmendment 2.

16.2 Lighting for traffic routes

Lighting for traffic routes is lighting designed primarily to meet the requirements of the driver of a motorised vehicle. Road lighting recommendations identify three distinct situations; trafficroutes where motorised vehicles are dominant and move without conflict, the edges of roadswhere pedestrians and cyclists may be at risk, and conflict areas where streams of motorisedvehicles intersect with each other or with pedestrians and cyclists.

16.2.1 Lighting recommendations for traffic routesThe primary function of the lighting of traffic routes is to make other vehicles on the roadvisible. Road lighting does this by producing a difference between the luminance of the vehicleand the luminance of its immediate background, the road surface. This difference is achieved byincreasing the luminance of the road surface above that of the vehicle so that the vehicle is seenin silhouette against the road surface.

The criteria used to define lighting for traffic routes are:

Average road surface luminance: The luminance of the road surface averaged over the carriageway(cd/m2).

Overall luminance uniformity (Uo): The ratio of the lowest luminance at any point on thecarriageway to the average luminance of the carriageway.

Longitudinal luminance uniformity (Ul ): The ratio of the lowest to the highest luminance foundalong a line along the centre of a driving lane. For the whole carriageway, this is the lowestlongitudinal luminance uniformity found for the driving lanes of the carriageway.

Threshold increment: A measure of the loss of visibility caused by disability glare from the roadlighting luminaires. Quantitatively, percentage threshold increment is given by the expression

TI = 65 (Lv / L0.8)

where : Lv = equivalent veiling luminance (cd/m2) (see section 2.6.3)L = average road surface luminance (cd/m2)

Surround ratio: The average illuminance just outside the edge of the carriageway in proportion tothe average illuminance just inside the edge of the carriageway.


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Traffic routes are divided into different classes. The different classes are based on the type ofroad, the average daily traffic flow (ADT), the speed of vehicles, the type of vehicles in the trafficand the frequency of conflict areas and pedestrians. Table 16.1 specifies the different classes andidentifies the recommend lighting criteria. Details of the recommended lighting criteria for dryroads are given in Table 16.2. These are the lighting criteria usually adopted in the UK.

Table 16.1 Lighting classes for traffic routes

Road name

Motorway

Strategic route

Main distributor

Road characteristic

Limited access

Trunk roads andsome main A roadsbetween primary

destinations

Major urbannetwork and

inter-primary links,short to mediumdistance traffic

Detailed description

Routes for fast moving, longdistance traffic. Fully grade

separated and restrictions on use

Main carriageway in complexinterchange areas

Main carriageway withinterchanges at < 3 km

Main carriageways withinterchanges > 3 km

Emergency lanes

Routes for fast moving, longdistance traffic with little

frontage access or pedestriantraffic. Speed limits are usuallyin excess of 40 mph and there are few junctions. Pedestrian

crossings are either segregated or controlled and parked

vehicles are usually prohibited

Single carriageway

Dual carriageway

Routes between strategic routesand linking urban centres to thestrategic network with limitedfrontage access. In urban areas,speed limits are usually 40 mph or less, parking is restricted at

peak times and there are positivemeasures for pedestrian

safety reasons

Single carriageway

Dual carriageway

ADT

< 40,000> 40,000

< 40,000> 40,000

< 40,000> 40,000

-

< 15,000> 15,000

< 15,000> 15,000

< 15,000> 15,000

< 15,000> 15,000

Lighting class

ME1ME1

ME2ME1

ME2ME2

ME4a

ME3aME2

ME3aME2

ME3aME2

ME3aME2


Lightingclass

ME1

ME2

ME3a

ME3b

ME3c

ME4a

ME4b

ME5

Minimummaintained average

road surfaceluminance (cd/m2)

2.0

1.5

1.0

1.0

1.0

0.75

0.75

0.50

Minimum overall

luminanceuniformity

0.40

0.40

0.40

0.40

0.40

0.40

0.40

0.35

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Road name

Secondarydistributor

Link road

Road characteristic

Classified road (B or C road) and

unclassified urban bus route, carrying

local traffic withfrontage access andfrequent junctions

Road linking themain and secondarydistribution network

with frontage access and

frequent junctions

Detailed description

Rural areas (Environmental zones 1 or 2). These roads link largervillages and HGV generators to

the strategic and main distributor network

Urban areas (Environmental zone 3). These roads have 30 mphspeed limits and very high levels of

pedestrian activity with somecrossing facilities including zebra

crossings. On-street parking isgenerally unrestricted except

for safety reasons

Rural areas (Environmental zones 1 or 2). These roads link smaller

villages to the distributor network.They are of varying width and not

always capable of carrying two-way traffic

Urban areas (Environmental zone 3). These roads are

residential or industrial inter-connecting roads with 30 mph

speed limits, random pedestrianmovements and

uncontrolled parking

ADT

< 7,0007,000–15,000

> 15,000

< 7,0007,000–15,000

> 15,000

Any

Any

Any with high

pedestrian orcyclist traffic

Lighting class

ME4aME3bME3a

ME3cME3bME2

ME5

ME4b or S2

S1

Table 16.1 Lighting classes for traffic routes

Table 16.2 Lighting recommendations for traffic routes

Minimumlongitudinalluminance

uniformity forthe carriageway

0.70

0.70

0.70

0.60

0.50

0.60

0.50

0.40

Maximumthresholdincrement

(%) (note 1)

10

10

15

15

15

15

15

15

Minimumsurround

ratio(note 2)

0.50

0.50

0.50

0.50

0.50

0.50

0.50

0.50


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In some situations, it may not be possible to calculate the maximum threshold increment. Analternative method to limit disability glare is to select a luminaire according to the classes givenin Table 16.3. The different classes are defined by the luminous intensity of the luminaire, incandelas/1000 lumens of bare light source output, at 70, 80 and 90 degrees from the downwardvertical, in any direction, and the luminous intensity above 95 degrees, in any direction. ClassG3 corresponds to a cutoff luminaire. Class G6 corresponds to a full cutoff luminaire.

Table 16.3 Luminaire classes for the control of disability glare

Lightingclass

G1

G2

G3

G4

G5

G6

Maximum luminousintensity/1000lumens at 70°(cd/1000 lm)

-

-

-

500

350

350


200

150

100

100

100

100


50

30

20

10

10

0

Luminousintensity

above 95° (cd)

-

-

-

0

0

0

Notes to Table 16.2Note 1. A five percentage point increase in minimum threshold increment is permitted where low luminance light sources,such as low pressure sodium and fluorescent, are used.

Note 2. The surround ratio criterion should only be applied where there are no traffic areas with their own criteriaadjacent to the carriageway.

16.2.2 Lighting recommendations for areas adjacent to the carriagewayPeople and objects adjacent to the carriageway need to be seen by the driver. Such locationsinclude unmade verges, footways and cycle paths and the emergency lanes of motorways. Forall traffic routes other than heavily used footways and cycle tracks and the emergency lanes ofmotorways, lighting of the area adjacent to the carriageway should conform to the surroundratio (Table16.2).

For traffic routes with heavily trafficked footways and cycle tracks an appropriate lightingcriterion should be selected from Table 16.4. Which criterion is selected will depend on thelighting class used for the carriageway. To ensure adequate illuminance uniformity, the actualmaintained average horizontal illuminance should not be more than 1.5 times greater than theminimum maintained average horizontal illuminance.

Emergency lanes on motorways should be lit to lighting class ME4a (see Table 16.2).


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Lighting class

S1

S2

S3

S4

S5

S6

Minimum maintained averagehorizontal illuminance (lx)

15

10

7.5

5

3

2

Minimum maintainedhorizontal illuminance (lx)

5

3

1.5

1

0.6

0.6

16.2.3 Lighting recommendations for conflict areasA conflict area is one in which traffic flows merge or cross, e.g. at intersections or roundabouts,or where vehicles and other road users are in close proximity, e.g. on a shopping street or at apedestrian crossing. Lighting for conflict areas is intended for drivers rather than pedestrians. Thecriteria used to define lighting for conflict areas are based on the illuminance on the road surfacerather than road surface luminance. This is because drivers’ viewing distances may be less thanthe 60 m assumed for traffic routes and there are likely to be multiple directions of view. Thecriteria used for the lighting of conflict areas are:

Average road surface illuminance: the illuminance of the road surface averaged over the carriageway (lx).

Overall illuminance uniformity (Uo): the ratio of the lowest illuminance at any point on thecarriageway to the average illuminance of the carriageway.

The recommendations for the different lighting classes for conflict areas are given in Table 16.5.These recommendations can be applied to all parts of the conflict area or only to the carriagewaywhen separate recommendations are used for pedestrians or cyclists (see Section 16.2.2).

The choice of lighting class has to be matched to the lighting of the traffic routes approaching theconflict area. Guidance is given in Table 16.6.

Table 16.5 Lighting recommendations for conflict areas

Lighting class

CE0

CE1

CE2

CE3

CE4

CE5

Minimum maintained averageroad surface illuminance (lx)

50

30

20

15

10

7.5

Minimum overall illuminance uniformity

0.4

0.4

0.4

0.4

0.4

0.4

Table 16.4 Lighting recommendations for areas adjacent to the carriageway


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A specific form of conflict area is the pedestrian crossing. Where a pedestrian crossing is close toa junction it is treated simply as part of the conflict area but where it occurs in isolation thereare two possibilities for lighting. One is to use the normal lighting of the traffic route with thecrossing positioned at the midpoint between luminaires. The other is to use additional locallighting. The local lighting approach is recommended when the traffic routes are lit to less thanlighting class ME3 (see Table 16.2) or the crossing is located on a bend, on the brow of a hill orwhere the relative positions of the crossing and road lighting luminaires cannot be coordinated.The local lighting should illuminate the crossing to a higher illuminance than is provided onthe roads approaching the crossing. A suitable lighting class for horizontal illuminance can beselected from Table 16.5. The local lighting should have strong vertical component to ensurethat pedestrians are positively illuminated but care must be taken to control glare towardsdrivers (Table 16.3).

16.2.4 CoordinationIt is obviously important that the lighting of conflict areas should be coordinated with that ofthe traffic routes. Table 16.6 indicates the compatible lighting classes for traffic routes andconflict areas. Where two traffic routes lit to different classes lead into a conflict area, the matchshould be made to the higher traffic route class.

Table 16.6 Compatible lighting classes for conflict areas on traffic routes

Traffic route lighting class

ME1

ME2

ME3

ME4

ME5

Conflict area lighting class

CE0

CE1

CE2

CE3

CE4

16.2.5 Traffic route lighting designFundamentalThe design process for traffic route lighting consists of the following stages:

Selection of the lighting class and definition of relevant area: the lighting class of the carriageway isselected (Table 16.1). The nature and extent of adjacent areas and any conflict areas areidentified and the lighting approach to be used chosen. The compatible lighting classes foradjacent areas and conflict areas are selected (Table 16.6).

Collection of preliminary data: the following data is required before calculation can start: mountingheight, luminaire type and optic setting, lamp type, initial luminous flux of lamp, IP rating ofluminaire, cleaning interval planned for luminaire, pollution category for location, luminairemaintenance factor, lamp replacement interval, lamp lumen maintenance factor at replacementinterval, maintenance factor, luminaire tilt, width of carriageway, width of driving lane, width ofadjacent areas, luminaire transverse position relative to the calculation grid, luminairearrangement, road surface r-table.


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The emphasis given to maintenance factors in this list arises from the fact that the lightingrecommendations are made in terms of minimum maintained values. Table 16.7 sets out typicalluminaire maintenance factors to be applied for different locations, luminaires and cleaningintervals. In this table, high pollution generally occurs in the centre of large urban areas andheavy industrial areas; medium pollution occurs in semi-urban, residential and light industrialareas while low pollution occurs in rural areas. Luminaires are classified by the protectionagainst foreign objects and dust number used in the IP system (see Table 4.10).

Table 16.7 Typical luminaire maintenance factors

The reflection properties of a road surface are quantified by an r-table. This consists of a matrixof values of q cos3 γ, where q is the luminance coefficient of the pavement material and γ is theangle of incidence of light from the upward vertical, in degrees (see Figure 16.1). This quantityis called the reduced luminance coefficient (r). The two dimensions of the r-table are the angleβ, the angle between the vertical plane of incidence and the vertical plane of observation and thetangent of the angle γ, the angle of incidence from the upward vertical (see Figure 16.1). Eachcell in the r-table contains a value for the reduced luminance coefficient multiplied by 10,000.

Luminaire IPclass/pollution level

IP2X/High

IP2X/Medium

IP2X/Low

IP5X/High

IP5X/Medium

IP5X/Low

IP6X/High

IP6X/Medium

IP6X/Low

Cleaninginterval = 12

months

0.53

0.62

0.82

0.89

0.90

0.92

0.91

0.92

0.93


months

0.48

0.58

0.80

0.87

0.88

0.91

0.90

0.91

0.92


months

0.45

0.56

0.79

0.84

0.86

0.90

0.88

0.89

0.91


months

0.42

0.53

0.78

0.76

0.82

0.88

0.83

0.87

0.90


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Figure 16.1 Angles upon which the luminance coefficient is dependent

In principle, the relevant angles for characterising the reflection properties of the road surfaceare: α = angle of observation from the horizontal, β = angle between the vertical planes ofincidence and observation, γ = angle of incidence from the upward vertical, and δ = anglebetween the vertical plane of observation and the road axis. In practice, for lighting of trafficroutes, it is assumed that α has a fixed value of 1 degree corresponding to a viewing distance ofabout 60 m and δ is irrelevant because the reflection properties of road surfaces are isotropic.

Although different road materials have different reflection properties, and those propertieschange over time and with wear, there are only two r-tables commonly used in the UK, one forasphalt-based roads and one for concrete roads. The r-table for the asphalt-based roads is calledthe representative British road surface. r-tables are characterised by two parameters, oneconcerned with lightness and one concerned with specularity. The parameter for lightness is theaverage luminance coefficient, Q0; this is highly correlated to the average luminance producedon the road surface. The parameter for specularity is

S1 = r (0, 2) / r (0, 0)

where: r (0, 2) is the reduced luminance coefficient for β = 0 degrees and tan γ = 2r (0, 0) is the reduced luminance coefficient for β = 0 degrees and tan γ = 0

S

β

δ

γ

α


The representative British road surface is characterised as Qo = 0.07 and S1 = 0.97. Forconcrete road surfaces the corresponding values are Qo = 0.10 and S1 = 0.24. There are otherr-tables available for different pavement materials. Where it is required to design for afrequently wet road, the calculations described below should be made using r-tables for bothdry and wet surfaces.

Calculation of design spacingThe design of road lighting for traffic routes to meet the selected criteria uses information onthe luminous intensity distribution of the luminaire, the layout of the luminaires relative to thecarriageway and the reflection properties of the road surface.

The luminous intensity distribution of the luminaire is supplied by the manufacturer.

The layout of the luminaires for two-way roads is usually single-sided, staggered or opposite. In a single sided installation all the luminaires are located on one side of the carriageway. Thesingle-sided layout is used when the width of the carriageway is equal to or less than themounting height of the luminaires. The luminance of the lane on the far side of thecarriageway is usually less than that on the near side. In a staggered layout, alternate luminairesare arranged on opposite sides of the carriageway. Staggered layouts are typically used where thewidth of the carriageway is between 1 to 1.5 times the mounting height of the luminaires. Withthis layout, care should be taken that the luminance uniformity criteria are met. In the oppositelayout, pairs of luminaires are located opposite each other. This layout is typically used whenthe width of the carriageway is more then 1.5 times the mounting height of the luminaires.

The layout of luminaires for dual carriageways and motorways is usually central twin, centraltwin and opposite or catenary. In a central twin layout, pairs of luminaires are located on asingle column in the central reservation. This layout can be considered as a single-sided layoutfor the two carriageways. Where the overall width of the road is wider, either because thecentral reservation is wider or there are more lanes, the central twin and opposite layout can beused. In this, the central twin luminaires alternate with the opposite luminaires to form astaggered layout. In the catenary layout, luminaires are suspended from a catenary cable alongthe central reservation. The catenary layout offers good luminance uniformity, less glarebecause the luminaires are viewed axially, and excellent visual guidance.

With an r-table matched to the pavement material, the luminous intensity distribution for theluminaire and the layout of the luminaires relative to the carriageway, the luminance producedby a single luminaire at any point P on the road surface can be calculated using the equation:

L =

where: L = luminance at the point P produced by the luminaire (cd/m2)I = luminous intensity in the direction from the luminaire to the point P (cd)r = reduced luminance coefficient at point Ph = mounting height of luminaire (m)

This process can then be repeated for adjacent luminaires and the contributions from allluminaires summed to get the luminance at that point for the whole lighting installation. This process can then be repeated over an array of points on the road so as to get the luminance metrics used to characterise the road lighting for traffic routes.

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Although this process can be done manually, for straight roads it is almost always done usingsoftware. This allows the designer to access the photometric file for the selected luminaire andthen to manipulate the mounting height, clearance, set-back, tilt and layout of the luminairesnecessary to determine the spacing required to meet the appropriate lighting criteria. Of thesevariables, clearance and set-back have limits. To allow safe passage, the clearance of all parts ofthe lighting equipment above the carriageway should be at least 5.7 m. To reduce the risk ofdeath or injury caused by collision with a lighting column, the minimum set-back of thelighting column from the edge of the carriageway is related to the design speed of the road, as listed in Table 16.8.

Table 16.8 Minimum set-back of lighting columns from the edge of the carriageway

Design speed for road (km/h)

50

60

100

120

Minimum horizontal set-back from the edge of the carriageway (m)

0.8

1.0

1.5

1.5

Bends in the road with a radius greater than 300 m can be considered as straight as far aslighting is concerned. For bends with smaller radii, the layout of the luminaires should bedesigned to ensure the necessary road surface luminance and good visual guidance. Where thewidth of the carriageway is less the 1.5 times the mounting height of the luminaires, theluminaires should be arranged in a single sided plan on the outside of the bend. For widerroads, an opposite layout should be used. A staggered layout should not be used on bends as itgives poor visual guidance. The spacing of luminaires on a bend is less than on a straight road,typically half to three quarters of the spacing on a straight road.

To check that the road surface luminance criteria are met for bends, an isoluminance templatecan be used. This consists of a contour on the road where the luminance from a singleluminaire is at 12.5% and 25% of the maximum road surface luminance. Given a layout ofluminaire positions, the luminance templates of the individual luminaires can be superimposedon the plan of the road to determine the luminance uniformity. Further details of this approachare given in BS 5489: Part 1.

Conflict areas have different shapes and use illuminance as a criterion rather than luminance.The illuminance produced at a point P from a single luminaire is given by the formula:

E =

where: E = illuminance at the point P from the luminaire (lx)I = luminous intensity in the direction from the luminaire to the point P (cd)γ = angle of the direction of I from the downward vertical (degrees)h = mounting height of luminaire (m)

I cos3 γh2


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This process can be repeated for adjacent luminaires and the contributions from all luminairessummed to get the illuminance at that point for the whole lighting installation. This process canthen be repeated over an array of points on the road so as to get the illuminance metrics usedfor the lighting of conflict areas.

Alternatively, manufacturers often provide a relative isolux diagram, this being the illuminancepattern provided on the road surface by a single luminaire relative to the maximum illuminanceand plotted in terms of mounting height. Given a layout of luminaires around a conflict area,the mounting height and information about the maximum illuminance, the overall illuminancepattern can be generated. Some suggested luminaire layouts for commonly occurring conflictareas, e.g. roundabouts, are given in BS 5489: Part 1 as is advice for special locations, such asbridges, elevated roads and around airfields. BS 5489: Part 2 provides guidance on the lighting of tunnels.

Plotting of luminaire positionsHaving determined the ideal spacing, the luminaire positions are identified, starting with theconflict areas. After these are settled, the luminaire positions for the traffic routes and adjacentareas are identified.

16.3 Lighting for subsidiary roads

16.3.1 Lighting recommendations for subsidiary roadsSubsidiary roads consist of access roads and residential roads and associated pedestrian areas,footpaths and cycle tracks. The main function of lighting of subsidiary roads and the areasassociated with them is to enable pedestrians and cyclists to orientate themselves and to detectvehicular and other hazards, and to discourage crime against people and property. The lightingin such areas can provide some help to drivers but it is unlikely to be sufficient for revealingobjects on the road without the use of headlamps. The main purpose of lighting footpaths andcycle tracks separated from roads is to show the direction the route takes, to enable cyclists andpedestrians to orientate themselves, to detect the presence of other cyclists, pedestrians andhazards, and to discourage crime against people and property.

Illuminance on the horizontal is used as the lighting criterion for subsidiary roads andassociated areas. The illuminances associated with each lighting class are given in Table 16.4.The lighting class to be used is determined by the traffic flow, the environmental zone, the levelof crime and the colour rendering of the light source used (Table 16.9). In this table, low trafficflow refers to areas where traffic is typical of a residential road and solely associated withadjoining properties. Normal traffic flow refers to areas where traffic flow is equivalent to ahousing estate access road. High traffic flow refers to areas where traffic usage is high and canbe associated with local amenities such as clubs, shopping facilities and pubic houses. The crimerates should be considered relative to the local area. The environmental zones (E1 to E4) are asdefined in Table 6.1. The divide in CIE general colour rendering index (CRI) at 60 means thatthe use of low pressure sodium or high pressure sodium light sources calls for a higherilluminance than fluorescent and metal halide light sources. The S-class may be increased onestep where there are traffic calming measures.


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Table 16.9 Lighting classes for subsidiary roads and associated areas, footpaths and cycle tracks

Crime rate

Low

Low

Moderate

Moderate

High

High

CRI

< 60

≥ 60

< 60

≥ 60

< 60

≥ 60

Lowtraffic

flow/E1 or E2

S5

S6

S4

S3

S2

S3

Normaltraffic

flow/E1 or E2

S4

S5

S3

S4

S2

S3

Normal traffic flow/E3

or E4

S3

S4

S2

S3

S1

S2

High trafficflow/E1 or E2

S3

S4

-

-

-

-

High trafficflow/E3 or E4

S2

S3

S1

S2

S1

S2

The area over which these illuminances should be applied varies with the application. Whenconsidering roads with associated areas, it is recommended that a single lighting class be applied tothe carriageway and any adjacent footway and verge, from boundary to boundary. If a road is ashared surface residential road, the relevant area is the shared surface only. When consideringfootpaths and cycle tracks separated from roads, consideration should be give to extending the litarea beyond the width of the footpath or cycle track so as to give a wider field of view.

Glare from luminaires should be controlled. To limit disability glare, where luminaires have clearbowls or reflectors, these should conform to at least class G1 of Table 16.3. For discomfort glare,the simplest approach is to select a luminaire where the light source is not visible, either directlyor as an image, from any relevant direction. If a more quantitative approach is desired, glare indexcan be used. This is calculated from the equation:

Glare index = I × A–0.5

where: I = maximum luminous intensity at 85° from the downward vertical, in any direction (cd)A = apparent area of the luminous parts of the luminaire on a plane perpendicular to the direction of I (m2).

Table 16.10 shows the glare index classes appropriate for subsidiary roads, footpaths and cycle tracks.

Table 16.10 Lighting classes based on glare index

Lighting class

D1

D2

D3

D4

D5

D6

Maximum glare index

7,000

5,500

4.000

2.000

1.000

500


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16.3.2 Lighting design for subsidiary roadsThe design process for lighting of subsidiary roads and associated areas, footpaths and cycletracks consists of the following stages:

Selection of the lighting class and definition of relevant area: the lighting class is selected (Table 16.9)and the relevant areas defined.

Collection of preliminary data: the following data is required before calculation can start: Mountingheight, luminaire type and optic setting, lamp type, initial luminous flux of lamp. IP rating of luminaire, cleaning interval planned for luminaire, pollution category for location,luminaire maintenance factor, lamp replacement interval, lamp lumen maintenance factor atreplacement interval, maintenance factor, luminaire tilt, width of relevant area, luminairetransverse position relative to the calculation grid, luminaire arrangement, glare index ofluminaire.

Calculation of design spacing: the calculation procedure for subsidiary roads and associated areas,footpaths and cycle tracks is given in BS EN 13201: Part 3, Section 7.

Plotting of luminaire positions: having determined the ideal spacing, the luminaire positions areidentified, starting with T-junctions, areas of traffic calming measures, and severe bends. Afterthese are settled, the luminaire positions for the straight sections of the roads, paths or tracks arefitted to match. Finally, a check is made to determine if the luminaire positions are compatiblewith possible column positions.

16.4 Lighting for urban centres and public amenity areas

Urban centres and public amenity areas are used by pedestrians, cyclists and drivers. In suchplaces, the lighting of the road surface for traffic movement is not the only or even the mainconsideration. Rather, the functions of lighting in urban centres and public amenity areas are todo what can be done for public safety and security, while also providing an attractive nighttimeenvironment. To fulfill these functions, a master plan should be produced to meet some or allof the following objectives:

to provide safety for pedestrians from moving vehicles

to deter anti-social behaviour

to ensure the safe movement of vehicles and cyclists

to match the lighting design and lighting equipment to the architecture and environment

to control illuminated advertisements and integrate floodlighting, both permanent and temporary

to illuminate road and directional signs

to blend light from private and public sources

to limit light pollution

to maintain lighting installations and protect them from vandalism

to facilitate CCTV surveillance.


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This battery of objectives and the individual nature of each site ensure that there is no standardmethod of lighting urban centres and public amenity areas, nor any universally applicablerecommendations. What can be given are some general recommendations for the illuminancesto be used in city and town centres, although even these may need to be adjusted for aparticular site, depending on the ambient environment, the level of crime, street parking etc.Table 16.11 lists the lighting classes recommended for city and town centres, based on the typeof traffic, the traffic flow, and the environmental zone (see Table 6.1). The minimummaintained illuminances associated with each lighting class are given in Table 16.5.

Guidance on some of the techniques used to light urban centres and public amenity areas aregiven in CIBSE LG 6: The outdoor environment and ILE/CIBSE Lighting the environment – A guide to good urban lighting.

Table 16.11 Recommended lighting classes for city and town centres

Type of traffic

Pedestrian only

Mixed vehicle andpedestrian with

separate footways

Mixed vehicle andpedestrian on the

same surface

Normal trafficflow/E3

CE3

CE2

CE2

Normal trafficflow/E4

CE2

CE1

CE1

High trafficflow/E3

CE2

CE1

CE1

High trafficflow/E4

CE1

CE1

CE1

16.5 Tunnel lighting

A tunnel can be defined as a section of road that is not exposed to the sky. Tunnels shorter than25 m do not need lighting. Tunnels longer than 200 m will need lighting by day and night.Tunnels between 25 and 200 m in length may need lighting by day and night. The nature oflighting provided will depend on the tunnel class, classes ranging from 1 to 4 depending on thetraffic density and traffic mix. The purpose of tunnel lighting is to enable drivers to see vehiclesand obstructions within the tunnel. The lighting of tunnels has to address two differentproblems. The first is the black-hole effect experienced by a driver approaching a tunnel. Thesecond is the black-out effect caused by a lag in adaptation on entering the tunnel. Neither ofthese problems occurs at night, because then the average road surface luminance inside thetunnel is recommended to be at least 1 cd/m2, a value similar to if not greater than that of theroad surface outside the tunnel (BSI 5489-2: 2003). By day, this is not the case. By day, theluminances around the tunnel portal will be much higher than those inside the tunnel so boththe black-hole effect and the black-out effect may be experienced and driver safety may suffer.

The black-hole effect refers to the perception that from the distance at which a driver needs tobe able to see vehicles and obstructions in the entrance to the tunnel, that entrance is seen as ablack hole. The major cause of the black-hole effect is the reduction in luminance contrasts ofthe retinal images of vehicles and obstructions in the tunnel entrance caused by light scatteredin the eye. There are two approaches that can be used to alleviate the black-hole effect. The firstis to reduce the luminance of the surroundings to the tunnel. This can be done by ensuringthat the tunnel portal is of low reflectance, by shading the tunnel portal and the road close tothe tunnel entrance with louvres designed to exclude sunlight, by using low reflectance roadsurface materials outside the tunnel and by landscaping to shield the view of high-luminancesources, such as the sky.


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The second is to increase the luminance contrast of vehicles and obstacles inside the tunnelentrance. This can be done by the choice of materials used in the tunnel entrance.

The road surface inside the tunnel entrance should be of higher reflectance than thatimmediately outside and the walls of the tunnel up to a height of 2 m, against which vehicles inthe tunnel are usually seen, should have a luminance within the range of 60 to 100 percent ofthe average road surface luminance, the actual minimum depending on the tunnel class.

The black-out effect occurs because although the approach to the tunnel starts the process ofvisual adaptation there is no guarantee that this process will be complete by the time the tunnelentrance is reached. The approach used to diminish the black-out effect is to gradually decreasethe road surface luminance from a threshold zone, starting at the tunnel portal, through atransition zone, to the interior zone. The length of these zones is determined by the stoppingdistance (SD), this being the distance required to bring a vehicle travelling at the maximumallowed speed to a complete halt. The length of the threshold zone is one SD. The average roadsurface luminance of the threshold zone is determined by the access zone luminance. Theaccess zone is the part of the road approaching the tunnel within one SD of the entrance portal.The access zone luminance is the average luminance of a conical field of view subtending 20degrees at the eye of a driver located at the start of the access zone and looking at the entranceportal. The threshold luminance ranges from 3 to 10 percent of the access zone luminancedepending on the tunnel class and the speed limit. The length of the transition zone isdetermined by the assumed vehicle speed, the distance being set so as to allow about 18 secondsfor adaptation. The road surface luminance of the interior zone in daytime depends on thespeed and density of traffic in the tunnel and covers a range of 0.5 to 10 cd/m2, the higher thespeed limit, the higher the traffic density and the more mixed the traffic, the higher the averageroad surface luminance recommended in the interior zone. The minimum overall uniformityratio along each lane of the tunnel should be 0.4 and the minimum longitudinal uniformityratio is in the range 0.6 to 0.7 depending on the tunnel class. Disability glare from lighting inthe tunnel is controlled by limiting the threshold increment to less than 15 percent. At the endof the interior zone is an exit zone where drivers leave the tunnel. The length of the exit zonein metres is numerically equal to the speed limit in kilometres/hour. The road surfaceluminance of the exit zone should be five times the average road surface luminance of the interior zone. Detailed guidance on the lighting of tunnels can be obtained from BS 5489-2: 2003.

As for the type of lighting used to provide the luminances in the tunnel, the light source mostcommonly used is one of the discharge sources, because of their high luminous efficacy, longlife and robustness. The luminaires used in tunnels have to be of rugged construction to dealwith vibration, dirt, chemical corrosion and washing with pressure jets. Three types of lightdistribution are used, symmetrical, counter-beam and pro-beam lighting. Symmetrical lightdistributions produce uniform luminance lighting throughout the tunnel so vehicles ofdifferent reflectances will have either positive or negative luminance contrasts with the road.Counter-beam light distributions are those where the light is directed predominantly againstthe traffic flow. This gives a high pavement luminance so that vehicles tend to be seen innegative contrast, but there is some risk of the driver experiencing discomfort and disabilityglare. Pro-beam light distributions are those where the light is directed predominately in thedirection of the traffic flow. This gives a low road surface luminance but high luminances forvehicles so the vehicles tend to be seen in positive contrast. Various claims have been madeabout the benefits of these different systems but no consensus about the best system has been reached.


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Finally, it is necessary to consider the potential for flicker and the consequent discomfort anddistraction to the driver. When tunnel lighting is provided by a series of regularly-spaced,discrete luminaires, there is always a possibility of flicker being perceived. It is recommendedthat care be taken to avoid spacing individual luminaires so that drivers moving at representativespeeds in the tunnel are not exposed to flicker in the range 2.5–15 Hz. Of course, flicker is onlya consideration if the lighting is provided by discrete luminaires. An alternative system based ona continuous linear luminaire through the tunnel avoids any flicker problem and provides goodvisual guidance for the tunnel, a feature that is particularly valuable where the tunnel curves.


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Chapter 17: Exterior workplace lighting

17.1 Functions of lighting in exterior workplaces

Exterior workplaces occur in many different forms. There are those that involve the movementof people, such as airports; those that involve the storage and movement of goods, such ascontainer terminals; those that involve the operation of large plant, such as an oil refinery; andthose that exist temporarily as happens during the construction of a building.

Regardless of the purpose of the site, the lighting systems of exterior workplaces have commonaims. In all exterior workplaces, the lighting is designed to ensure the safety of people workingon the site and to enable the work to be done quickly and easily, without discomfort.


When designing lighting for exterior workplaces, there are a number of factors that need to be considered.

17.2.1 ScaleThe scale of the equipment to be used on the site is important in determining the lightingapproach. Some industries, such as the chemical industry, have plant that is large and complex sothere is no possibility of separating the lighting from the plant. As a result, the lighting has to beintegrated into the plant (Figure 17.1).

Figure 17.1 Lighting of a chemical complex

Others are large and simple and can be lit by simple area floodlighting. Yet others are small andhave a limited number of lines of sight, e.g. loading bays.

17.2.2 Nature of workThe nature of the work in exterior workplaces can vary widely. All exterior workplaces requirelighting for safe movement but beyond that the need for fine visual discrimination and where itis needed is uncertain and may vary from day to day. In these circumstances, considerationshould be given to using localised lighting where fine visual discrimination is always neededand mobile lighting for places where fine visual discrimination may be needed in differentlocations at different times. Some lighting will also be required where working at night exposesthe workers to danger (Figure 17.2).


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17.2.3 Need for good colour visionWhere colour is used to convey information, lighting with good colour rendering properties isrequired. For example, in chemical plants, it is common to use colour to identify the contentsof pipes. For such applications, a light source with a CIE general colour rendering index of atleast 60 is recommended.

17.2.4 ObstructionMany exterior workplaces contain obstructions, e.g. stacked shipping containers. Obstructionstend to produce shadows. Shadows can be minimised by:

using high mounted floodlights with a wide light distribution so that light reaches every point from more than one direction

having high-reflectance surfaces such as concrete rather than tarmac hard standing

providing local lighting of the shadowed area.

17.2.5 Interference with complementary activitiesSome common exterior workplaces are interfaces between one mode of transport and another,e.g. railway yards, airports and docks. Care should be taken to ensure that train drivers, aircraftpilots and ships’ pilots approaching the facility can see and understand all the relevant signals.They may experience difficulty in doing this either because of low visibility caused by disability glare or because of confusion caused by similarity between signal lights and theworkplace lighting.

17.2.6 Hours of operationNot all exterior workplaces operate throughout the night. If this is the case, considerationshould be given to switching to security lighting after the end of work (see Section Chapter 18).Even when the site is active throughout the night, it is often the case that the number of staffinvolved is small. If this is the situation, consideration should be given to a switching systemwhich allows different parts of the site to be lit or unlit according to the needs of the work.

Figure 17.2 A mobile luminaire usedto provide lighting in atemporary work zone


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Activity

Safe pedestrianmovement in low

risk areas

Safe movement of slow vehicles

Safe movement inmedium risk areas

Normal traffic

Very rough work

Rough work

Safe movement in high risk areas

Normal work

Fine work

Minimummaintained

meanilluminance (lx)

5

10

20

20

20

50

50

100

200

Illuminanceuniformity(minimum/

average)

0.15

0.25

0.25

0.4

0.25

0.25

0.4

0.4

0.5

Typical applications

Industrial storage areas withonly occasional traffic

Open storage areas served byfork lift trucks

Vehicle storage areas, containerterminals with frequent traffic

Road lighting in containerterminals, marshalling yards

Excavation and site clearance

Handling timber

Critical area within chemicalplants, oil refineries etc

Brick laying, carpentry

Painting, electrical work

17.2.7 Impact on the surrounding areaExterior workplace lighting should be limited to the site. Stray light from a site may beconsidered to be light trespass by neighbours and a source of sky glow by others (see Section6.2.9 and SLL Factfile 7: Environmental considerations for exterior lighting).

17.2.8 Atmospheric conditionsSome exterior workplaces are difficult environments for lighting equipment. Chemical plantsmay produce a corrosive atmosphere. Oil refineries have a flammable environment. Coastalcontainer terminals will expose luminaires to a high level of salt.


17.3.1 Illuminance and illuminance uniformityThe recommendations for exterior workplace lighting involve maintained mean illuminance,illuminance uniformity, glare control and light source colour properties. The maintained meanilluminances listed are minima on the relevant plane. The illuminance uniformity is measuredover the relevant area which can range from the whole site to a small part of the site. Exteriorworking activities are very diverse. Table 17.1 gives some lighting recommendations for genericactivities. Recommendations for specific industries can be found below and in the SLL Code forlighting and the SLL Lighting Guide 1: Industrial lighting.

Table 17.1 Illuminance recommendations for exterior workplaces


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17.3.2 Glare controlGlare control for outdoor lighting is quantified by the glare rating. Glare rating (GR) is given bythe formula

GR = 27 + 24 ln

where: Lv = equivalent veiling luminance produced by the luminaires at the eye (cd/m2)Le = equivalent veiling luminance produced by the environment at the eye (cd/m2)

See Section 2.6.3 for more information on the calculation of equivalent veiling luminance.

For many applications, Le is approximated by the formula Le = 0.035 E ρ / π where ρ is thereflectance of the surface, e.g. a sports field, and E is the illuminance on the field (lx). For grasssports fields, a reflectance in the range 0.15 to 0.25 is appropriate.

The higher the glare rating, the greater is the visual discomfort. It is necessary to calculate glarerating for all critical viewing directions.

17.3.3 Light source colour propertiesLight source colour properties are important for naming colours, something that can besignificant where colour coding is used for identification. The ability to name colours accuratelyand confidently is determined by the light source spectral power distribution and theilluminance. Any light source with a CIE general colour rendering index greater than 60 willallow accurate and confident colour naming at the illuminances recommended for public spacesat night. High pressure sodium lamps allow accurate but less confident colour naming at thehigher illuminances recommended for public spaces but both the accuracy and confidencedecline at lower illuminances. Low pressure sodium lamps do not allow accurate colour namingunder any illuminance and any confidence felt about being able to name colours is misplaced.

17.3.4 Loading areasMany industrial premises have a loading bay (Figure 17.3). The two key points to rememberabout a loading bay is that there should be no glare to the driver backing up to the loading bayand when backed up the vehicle may cause shadows over the working area. Luminaires on aloading bay are exposed to the weather so they should have the appropriate IP rating (see Table4.10). For loading bays with a canopy height less than 6 m, a suitable approach is to use pairs ofluminaires fitted with fluorescent lamps, one mounted either side of the bay door. Where thecanopy is more than 6 m high, luminaires using high intensity discharge lamps can be usedinstead of fluorescent lamps provided care is take to avoid glare to the driver. An alternativemounting position for such luminaires is at the front of the canopy aimed towards the bay door.To enable workers to see inside a vehicle it can be helpful to place a low wattage floodlightabove the loading bay door. These luminaires should not be switched on until after the vehiclehas been backed up. Care should be taken to minimise glare to workers leaving the vehicle.

Outdoor loading areas are usually lit by area floodlighting, either mounted on a building or onpoles or masts. Such lighting should provide uniform illumination without glare to peopleworking in the area, particularly fork lift truck drivers whose viewing direction may frequentlybe upward.

Lv

L0.9e


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Figure 17.3 Lighting of a loading bay

Application

Loading bay

Outdoor loading area

Horizontalilluminance (lx)

150

100

Horizontalilluminanceuniformity

-

0.5

Maximumglare rating

-

45

Minimumcolour

rendering index

40

20

Table 17.2 Lighting recommendations for loading

17.3.5 Chemical and fuel industriesSome parts of these industries have large outdoor facilities. Some such facilities are open e.g. acoal stockyard, while others are complex structures with platforms at many different levels e.g.an oil refinery. For the former, lighting is usually done by conventional area floodlightingtechniques. For the latter, lighting is done by integrating luminaires into the plant.

Luminaires in these facilities are often exposed to adverse conditions. These may range from avery dirty atmosphere, as in a coal and ash handling area, through corrosive atmospheres, as insome chemical plants, to risks of fire and/or explosion, as in the oil and gas industries wherewhole plants are considered hazardous areas. Luminaires that are capable of dealing with theprevailing conditions need to be used (see Section 4.3.2). Consideration also needs to be givento ensuring easy access to luminaires for maintenance. The lighting recommendations for thechemical and fuel industries are given in Table 17.3. The approach to designing lighting for the outdoor areas of these industries is discussed in Section 17.4.


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Table 17.3 Lighting recommendations for chemical and fuel industries

Activity

Handling servicing tools,adjusting manual valves,

starting and stoppingmotors, lighting ofburners, operating

switch gear

Moving on walkways

Filling and emptyingtrucks and wagons with

risk free substances,inspection of pipes

and packages

Fuel loading andunloading sites

Filling and emptyingtrucks and wagons withdangerous substances,replacement of pump

packing, general servicework, reading of

instruments

Repairs of machines and electric devices


0.25

-

0.4

0.4

0.4

0.5

Maximumglare rating

55

-

50

45

45

45

Minimumcolour

rendering index

20

-

20

20

40

60


20

50

50

100

100

200

17.3.6 Sidings, marshalling yards and goods yardsThese railway facilities can cover large areas. Lighting is usually done by conventional areafloodlighting but there are two features that require special attention. The first is the level ofobstruction caused by the closeness of wagons on adjacent lines. The second is the need toensure good visibility of all signals. To avoid shadows between wagons, confusion with signalsand glare to workers, a high mast lighting installation is commonly used.

The masts should be positioned near to those areas that require higher illuminances (see Table17.4). The floodlights should be aimed along the tracks. This aiming minimises shadowsbetween adjacent wagons and takes advantage of specular reflections to reveal the run of the rails.Where lighting has to be across tracks, reflections from wagon sides make an importantcontribution to the illumination between wagons. This contribution will only be important if theangle of incidence is more than 45 degrees (Figure 17.4). The lateral spacing of floodlightsshould not be more than twice the difference between the height of the floodlights and theheight of the wagons.


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Figure 17.4 High mast lighting of a railway yard with reflections from wagons

Table 17.4 Lighting recommendations for sidings and railway yards

Location

Railway yards, flat marshalling, retarder and

classification yards

Hump areas

Freight track, short duration operations

Open platforms in freight areas

Servicing trains andlocomotives

Railway yards handling areas

Coupling area

Covered platforms in freight areas, short duration operations

Covered platforms in freight operations,

continuous operations


0.4

0.4

0.25

0.4

0.4

0.4

0.4

0.4

0.5

Maximumglare rating

50

45

50

50

50

50

45

45

45

Minimumcolour

rendering index

20

20

20

20

40

20

20

20

40

Horizontalilluminance

(lx)

10

10

10

20

20

30

30

50

100

Hw

Max 45˚

S

Hm


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17.4 Approaches to exterior workplace lighting

17.4.1 High mast floodlighting Many large area sites, such as container terminals, railway marshalling yards and car storage areasuse high mast floodlighting. A smaller number of high masts are preferred over a larger numberof lower masts for reasons of economy and because they allow greater freedom of movement inthe area illuminated.

The most economical mast height is usually between 20 and 30 m. At greater heights, the costsof the masts increase greatly while at lower heights, the numbers of masts, lamps and luminairesincrease dramatically. A lower mast height can be justified where there is extensive obstruction.

The usual light sources for high mast lighting are either high pressure sodium or metal halidedischarge lamps. The luminaires used are floodlights with the light distribution matched to theproposed spacing of the masts. The luminaires should be suitable for the atmosphericconditions. This means that, at the very least, the luminaire should have the necessary IPnumber (see Table 4.10) and may require protection against corrosion and explosiveatmospheres.

17.4.2 Integrated lightingOil refineries, cement plants and similar sites are usually lit by integrating the lighting into theplant (Figure 17.5). This is typically done by selecting a luminaire with a very wide lightdistribution, both up and down, and bolting it onto convenient parts of the structure so as tolight all parts of the structure. The result is that too often the plant is lit up like a Christmas tree.

Figure 17.5A cement plant with lightingintegrated into the structure

Increased sensitivity to light pollution should mean that this approach is no longer acceptable. It is still necessary to integrate the lighting into the structure but to reduce light pollution it isnecessary to be more careful about the type of luminaire selected, more informed about suitablelocations for those luminaires and more adventurous about the control of the lighting at night.The luminaire selected should provide a predominantly downward light distribution, ideallywithin 70 degrees about the downward vertical. This more restricted light distribution willrequire more care in the positioning of adjacent luminaires to ensure they are providing enoughlight for safe access and work, without leaving dark spots. As for controls, the number of peopleworking at night to keep the plant running is often small and they are unlikely to want access toall parts of the plant at all times. Simple switching controls located in a control room can be usedto light those parts of the plant in which people are working, as necessary.


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17.4.3 Localised lightingIn many exterior workplaces, the places where detailed visual work is carried out are limited. Inthis situation, there is little point in lighting the whole site to the level necessary for the detailedwork. A better approach is to light the whole site to the level necessary for safe movement and touse localised lighting for the work areas. This localised lighting may be permanent, for a fixedworking area, or temporary, for a construction site. The latter lighting may be powered from a generator.


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Chapter 18: Security lighting

18.1 Functions of security lighting

Security lighting is installed to help protect people and property from criminal acts. Otherforms of lighting, such as outdoor display lighting, decorative floodlighting, shop windowlighting and park lighting, can contribute to this goal, but they are designed with additionalcriteria in mind (see CIBSE Lighting Guide 6: The outdoor environment).

Lighting can help to protect people and property from criminal activities because of its effect onvision (Boyce 2003). In public spaces, good security lighting is designed to help everyone seeclearly all around. This means that people approaching can be easily identified and that otherpeople’s activities can be seen from a distance. This has the effect of shifting the odds in favourof the law-abiding and against the criminal. The law-abiding are unlikely to be taken bysurprise, while criminals are more uncertain about whether their activities have been witnessedor they have been recognised. In secure spaces to which the public does not have access, it ispossible to use lighting to enhance the vision of guards while hindering the vision of potentialintruders.

Lighting is only one part of a security system. The complete system usually includes a physicalelement, such as fences, gates and locks; a detection element, involving guards patrolling orremote surveillance; and a response element, which determines what is to be done afterdetection occurs. Unless security lighting is integrated into the complete system, it is unlikelyto be successful. For example, good lighting in a storage area that nobody is watching, andhence in which there is no possibility of a response, will simply help intruders do what theywant to do, more quickly.


The characteristics of the lighting to be used as part of the security system will be determinedby various features of the site. The factors that always need to be considered are the following.

18.2.1 Type of siteSites can be conveniently classified by the extent to which people have access to the site and thepresence or absence of physical defences such as fences. Broadly, there are three types of site.

secure areas, where there are physical defences and to which access is controlled, such as a fenced storage yard (Figure 18.1)

public areas, where people may be present at any time and which have no physical defences, such as a shopping centre car park (Figure 18.2)

private areas, where there are no physical defences but where the general public is not expected to be present, such as a house (Figure 18.3).


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Figure 18.1Lighting of a secured area, a fenced storage yard

18.2.2 Site featuresOne feature of a site that can have a major influence on the type of security lighting adopted isthe extent to which the site is obstructed. Where a single building occupies a significant part ofthe site and contains the only items of value, it may be more effective to floodlight the buildingrather than to light the whole site. Where there are multiple obstructions, as in a containerterminal, the whole site should be lit in a way that minimises shadows. Another importantfeature is the average reflectance of the surfaces within the site. High reflectance surfacesincrease the amount of inter-reflected light and this diminishes both shadows and glare. Figure 18.4 shows what happens when glare is combined with obstruction and low reflectance surfaces.

Figure 18.4A business yard lit by two highpower floodlights. Thecombination of a narrow lightdistribution, obstruction andlow surface reflectances resultsin strong shadows and glare

Figure 18. 2Lighting of a public area, ashopping centre car park

Figure 18.3Lighting of a private area,a house driveway


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18.2.3 Ambient light levelsThe illuminances produced by the security lighting need to at least match or preferably exceedthe illuminances of the surrounding area. Unless, this is done, the area covered by the securitylighting will look dimly lit.

18.2.4 Crime riskThe frequency and nature of crimes occurring in different locations can vary widely. The levelof risk will already be built into the level of defences used on secure sites but this is not possiblein public areas. In public areas, increasing risk of crime is associated with increasingilluminances used for security lighting.

18.2.5 CCTV surveillanceCCTV cameras are widely used for remote surveillance of large areas. The amount of lightrequired for effective operation of CCTV cameras can vary dramatically from starlight to high-level security lighting. Manufacturers specify a minimum illuminance needed for their camerasto produce a clear picture. These values usually assume an incandescent lamp. Higherilluminances may be required for other light sources with different spectral power distributions.Further, if moving objects are to be easily seen, illuminances above the minimum will berequired, whatever the light source. The manufacturer should be consulted before selecting thelight source to be used if there is any doubt about the sensitivity of the camera.

The other aspect of cameras that needs care is their rather limited dynamic range. A high levelof illuminance uniformity is necessary if dark areas in the CCTV image are to be avoided.Further, care should be taken to mount CCTV cameras in positions where they do not receiveany light directly from the luminaires as such light will sometimes cause a ‘white-out’ of thatpart of the image.

18.2.6 Impact on the surrounding areaSecurity lighting should be limited to the protected area. Stray light from a security lightinginstallation may be considered to be light trespass by neighbours and a source of sky glow byothers (see Section 6.2.9). Further, where signal lights are used to control traffic on roads andrailways, care should be taken to avoid confusion caused by either disability glare to theobserver, veiling reflections on the signals, or the identification of the security lighting itself as a signal.


18.3.1 Illuminance and illuminance uniformityThe recommendations for security lighting involve maintained mean illuminance, illuminanceuniformity, glare control and light source colour properties. The maintained mean illuminanceand illuminance uniformity recommendations are given for secure areas and public areasseparately. The recommendations for glare control and light source colour properties areapplicable to both. The maintained mean illuminances listed are minima. It may be necessary to increase these illuminances where the ambient light levels and the risks of crime are high.


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Table 18.1 Illuminance recommendations for security lighting of secure areas

Table 18.2 Illuminance recommendations for security lighting of public areas

Application

Large open areas, e.g.storage yards

Building facades

Fences

Entrances/gatehouses

Minimummaintained


5

5

5

100


average)

0.1

0.1

0.1

-

Notes

The illuminance is measuredon the horizontal surface ofthe area, using the method

given in BS 5489-1

The illuminance is measuredon the building facade

The illuminance is measuredon the ground on either side

of the fence

The illuminance is measuredat ground level. In addition, avertical illuminance of 25 lxshould be provided at thelevel of the vehicle driver

Application

Light traffic and lowcrime risk car parks

Medium traffic ormedium crime risk

car parks

Heavy traffic or highcrime risk car parks

Public parks

Service station,pump area

Service station,store front

Minimummaintained


5

10

20

10

50

30


average)

0.25

0.25

0.25

0.25

0.33

0.33

Notes

The illuminance is measuredon the ground, using the

method given in BS 5489-1





The illuminance is measuredon the ground of pathways

The illuminance is measured on the ground

The illuminance is measured on the ground


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18.3.2 Glare controlGlare control for outdoor lighting is quantified by the glare rating. The glare rating is calculatedusing the method set out in CIE Publication 112: 1994 (see Section 17.3.2 for details) and inthe SLL Code for lighting. The glare rating will vary with viewing direction. For altitude, it isusually assumed that the observer is looking 2 degrees below the horizontal. For azimuth,calculations are done in 45 degree steps around the observation point.

It is important when designing security lighting to be clear about the value of glare. Where clearvisibility at a distance is important to those guarding a secure area or those using a public area,glare needs to be carefully controlled. A glare rating of 30 or less is recommended. This canusually be achieved by eliminating any direct view of the light source for all luminairesmounted below 5 m. Where the security lighting is to be used to make it difficult for potentialintruders to see into a site, glare is a positive so a direct view of the light source and a lowmounting height are encouraged. For such applications, a glare rating of 70 or greater is recommended.

18.3.3 Light source colour propertiesLight source colour properties are important for naming colours, an element in many witnessstatements. The ability to name colours accurately and confidently is determined by the lightsource spectral power distribution and the illuminance. Any light source with a CIE generalcolour rendering index greater than 60 will allow accurate and confident colour naming at theilluminances used in public spaces at night. High pressure sodium lamps allow accurate but lessconfident colour naming at the higher illuminances used for public spaces but both theaccuracy and confidence decline at lower illuminances. Low pressure sodium lamps do notallow accurate colour naming under any illuminance and any confidence felt about being ableto name colours is misplaced (Saalfield, 1995).

18.4 Approaches to security lighting

18.4.1 Secure areas The first question to consider is whether to light the space at all. It can be argued that lighting asecure area advertises the presence of something worth taking and hence attracts criminals, sokeeping the area dark is a better approach. However, if the criminal already knows the areacontains valuable materials, then the absence of lighting makes the secure area more difficult todefend. Thus the choice of whether to light or not depends on the owner’s assessment of risk.If the risk of criminal activity is high, lighting is desirable. If the risk of criminal activity is low,then providing lighting may be counterproductive.

Area lighting: area lighting is commonly used in large open areas such as storage yards andcontainer terminals. Typically, these sites are lighted uniformly by floodlighting or roadwayluminaires on poles 10 m or more in height. For typical roadway and floodlighting luminairesmounted singly on poles, the desired illuminance uniformity can be achieved by spacing theluminaires at six times their mounting height. The actual spacing will depend on the luminousintensity distribution of the luminaire.

If the area is unobstructed by trees, structures or topography, the most economic installationwill be one very tall pole carrying many high-wattage lamps. However, this solution is a falseeconomy as it also produces the poorest illuminance uniformity, the harshest shadows, and thegreatest amount of light trespass. If the area contains obstructions, as in container terminals, adesign utilising multiple source locations will reduce shadowing.


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This is especially true if the luminaires are positioned within the site, between obstructions, andwith overlapping light patterns. Reflectance of site materials can also be used to advantage. Ifthe owner uses containers that are painted a highly reflective colour, or paves the area withconcrete rather than asphalt, light diffusely reflected from these surfaces will diminish thedepth of shadows.

Building facades: security lighting for building exteriors is based on the principle that all points ofentry to the building and the areas around them should be easily seen. Depending on theconstruction of the building, the points of entry can consist of walls and roof as well as doorsand windows. The most comprehensive approach is to light the whole building. Securitylighting for buildings is more effective if the building has a high reflectance facade and the areaadjacent to the building also has a high reflectance.

Figure 18.5Lighting of a complete building facade

The building can be lighted by luminaires set in the ground, mounted on the building ormounted on poles (Lyons, 1980; Leslie and Rodgers, 1996). Ground-mounted floodlights canprovide uniform building lighting but they are very accessible and hence can easily besabotaged. Luminaires mounted on the building are more economical than pole-mountedluminaires, since the expense of the pole is eliminated and wiring costs are reduced.However, for anything other than a simple rectangular building, it is difficult to adequatelyilluminate all of the building surfaces without using an excessive number of luminaires. Pole-mounted luminaires are usually the best option for uniformly lighting the surfaces ofbuildings and the surrounding area.

Perimeter fences: the purpose of lighting perimeter fences is to enable guards to detect intrudersloitering outside the fence or attempting to get over or through the fence. Fences come inseveral different forms from masonry through steel palisades to chain link. The form oflighting used will depend on the possibility of seeing through the fence and whether one orboth sides of the fence line are to be patrolled.

If the fence is solid, there is no possibility of seeing through it. Nonetheless, if both sides ofthe fence are to be guarded, lighting can be provided on both sides by positioning a luminairedirectly above the top of the fence. The luminaire should be located well above the top of thewall to reduce the shadowed area at the base of the wall.

If a view through the fence is possible, and if the fence is patrolled from either inside oroutside the secure area, it is useful to be able to see both sides of the fence from one side. For this to happen, light needs to be provided on both sides. This can be done from pole-mounted fixtures set back from the fence (Lyons, 1980).


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gThe lighting will be most effective if the luminance of the fence is lower than the luminance ofthe area on the side being viewed through the fence (Boyce, 1979). This objective can beachieved by using a low-reflectance fence material such as black or dark green-coated chain-link. If galvanised chain link is used, care should be taken with the aiming of the luminaires toreduce the illuminance directly onto the fence.

Lighting designed to deliberately produce disability glare to people outside a fence can be usedfor perimeter fences enclosing large areas, in remote locations where there is no other sitelighting (Lyons, 1980). In this system, a line of high-luminance luminaires is mounted at eyelevel and aimed outward from the secure area. For glare lighting to be effective, the secure areashould not be otherwise illuminated, any fence material should be of low reflectance and theluminaires should be closely spaced. Further, patrol roads or paths should be located within theperimeter fence, behind the line of the glare lighting luminaires.

Care should be taken to locate the luminaires far enough inside any perimeter fence line toguarantee that the intruder cannot get between the luminaire locations and still view the securearea from outside the fence. This approach should be used with caution because of thelikelihood of light trespass to nearby residents and visual discomfort to passers-by.

Entrances and gatehouses: access to a secure area is usually controlled by security personnel whoseduty is to stop and inspect people and vehicles entering and leaving the site. At most exposedlocations, a gatehouse will be provided. The entrance should be equipped with multipleluminaires so the loss of any one luminaire will not seriously degrade the lighting available tothe guard on duty (Leslie and Rodgers, 1996).

All vehicle entrances should have luminaires located so as to facilitate complete inspection ofvehicles and their contents. Lights should be located to illuminate the vehicle license plate.Where on-coming vehicles approach the guardhouse, signs may be appropriate instructingdrivers to turn off headlamps. In high security areas, some luminaires should be mounted at ornear ground level to facilitate inspection of the underside of the vehicle.

These luminaires can be controlled with a manual switch or remote sensing device. Having aconcrete road surface to increase the reflected light will help in the inspection of the undersideof vehicles. Consideration should be given to providing back-up power supplies for use duringelectrical outages.

Care should be taken to provide good vertical illuminance so as to allow for facial identification, inspection of credentials, and packages without use of auxiliary hand-held devices such as flashlights.

Illumination inside the guardhouse should be limited to the minimum required for thecompletion of assigned tasks, such as report writing and equipment use. The ability to reducethe illuminance is necessary to allow the guard to see clearly through the windows at night andto limit the ability of someone approaching the gatehouse to see what the guard is doing inside.Well-shielded task luminaires are essential to avoid reflections on any surveillance monitors andthe windows of the gatehouse. Fitting the gatehouse with specular-reflecting, low-transmissionglass at a tilted angle, painting the inside of the gatehouse in dark colours and ensuring thatillumination can be dimmed will all help limit the view into the gatehouse (Lyons, 1980).


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Deg

ree

of

agre

emen

t

0

Horizontal illuminance (lx)

50 100 150 200

5

3

1

–1

–3

–5

= Male

= Female

= Male

= Female

18.4.2 Public spacesThe ultimate aim of the lighting of public spaces is to make the space look attractive and safeand hence encourage its use at night (Leslie and Rodgers, 1996). Lighting can contribute to thisperception by allowing action at a distance. What this means is that by enhancing the visibilityof people and faces, suspicious or threatening behaviour may be detected early enough for anescape to be made. Similarly, greater visibility provided by lighting may enable people behavingin a suspicious manner to be recognised or at least described. Such observations at a distance area benefit to the law-abiding and a disadvantage to the criminal.

Lighting designed to allow action at a distance requires that attention be paid to the illuminanceprovided, the uniformity of illuminance, the presence of disability glare and the spectral powerdistribution of the light source. For people to have a reasonable perception of safety at night incar parks and on business streets, the horizontal illuminance on the ground should liesomewhere between 10 and 50 lx depending on the ambient illuminance (Figure 18.6). Below10 lx, perceptions of safety deteriorate rapidly. Above 50 lx, perceptions of safety are close to themaximum possible, so there is little more to gain from higher illuminances (Boyce et al, 2000).

Figure 18.6 Mean levels of agreement with the statement ‘This is a good example of securitylighting’ plotted against horizontal illuminance, for sites in New York City and Albany, NY, formale and female subjects separately. A value of +5 indicates strong agreement and –5 indicatesstrong disagreement (after Boyce et al., 2000).

As for illuminance uniformity, if the principal of action at a distance is to be followed, it isessential that excessive variations in illuminance be avoided. Close spacing of luminaires isparticularly important if excessive variation in the vertical illuminances on faces is to beavoided. To avoid excessive variation in vertical illuminance, the spacing used should be lessthan two thirds of the maximum spacing suggested by manufacturers.

The most common sources of disability glare at night are luminaires in unsuitable locations,poor aiming of luminaires or poor luminaire design. This last problem is particularly commonin ‘historic’ luminaires, which combine little shielding of the light source with low mountingheights. Care in the selection of luminaires, their aiming and mounting heights are essential ifdisability glare is to be avoided.


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Service stations and mini-marts: these locations are often round-the-clock operations. A minimummaintained mean illuminance of 50 lx on the ground is recommended for all parking andcustomer use areas, including petrol pumps and islands, and air and water stations. Surroundingareas should be illuminated to a minimum maintained mean illuminance of 30 lx. A minimumvertical illuminance of 10 lx at 1.5 m above ground level should be provided for lighting faces(Figure 18.8).

Car parks: the recommended minimum maintained mean illuminance for car parks depends onthe level of traffic and the risk of crime (Table 18.2). Where traffic is light and the risk of crimeis low, a minimum maintained mean illuminance of 5 lx is adequate. More traffic or greatercrime risk implies higher illuminances for security lighting (CIBSE Factfile 2: Car park lighting –A dilemma resolved). Car parks are usually lit by pole-mounted luminaires arranged around andwithin the car park (Leslie and Rodgers, 1996).

Parks: parks and similar areas are intended for the pleasure and relaxation of the public but it isdifficult to relax if one is worried about the possibility of assault. Lighting of such sites requiresthat people visiting the park should be able to see clearly all around them without destroyingthe ambience of the park. There are many different approaches that can be used, ranging fromconventional path lighting to landscape lighting (Figure 18.7) (CIBSE Lighting Guide 6: Theoutdoor environment; Leslie and Rodgers, 1996).

Figure 18.8Lighting of a service station

Figure 18.7Lighting in a small park

18.4.3 Private areasSecurity lighting for private houses differs from the lighting provided for secure areas and publicspaces because houses usually do not have the physical defences of secure spaces although it is notdesirable to have the public using the space. The size of the house, the distance from neighbours,the nature of the terrain and whether the house is in a rural, suburban or urban area are all factorsto be considered. Deterrence is usually the number one priority in residential security, followedby detection, recognition and, if all else fails, a signal for help.


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Figure 18.9A recessed doorwaywith lighting at thesides of the door

Illumination at the front entrance is mainly for the identification of callers. Luminaires oneither side of the door aid recognition by lighting the face from two directions (Figure 18.9).Luminaires should not be located directly above or behind where a person at the doorwould be standing. The minimum vertical illuminance at head height should be 10 lx (Van Bommel and Van Dyk, 1984).

The front, back and sides of the house are best illuminated using luminaires mounted on thebuilding itself. This method increases the illumination on the face if the correct luminaires areselected and should be controlled with a motion sensor. As a person approaches, the sensor willactivate the luminaires, confronting an intruder with a well-lit environment.

The minimum maintained vertical illuminances for the surfaces of a private house should be inthe range 5 to 20 lx, the actual illuminance being determined by the risk of crime and theambient illuminance. The minimum maintained minimum/average illuminance ratio for allsurfaces is 0.25.

18.4.4 Multi-occupancy dwellings Multi-occupancy dwellings present additional security lighting challenges to those posed bysingle-family houses. Outside the dwelling, the challenges are the same as for single-familyhouses and can be dealt with as described above (Leslie and Rodgers, 1996) but when theoccupants are inside the building, they are not in a totally secure environment. The building isaccessible to the other residents and their guests so occupants may be at risk when movingabout within the building.

For hallways, stairways and laundry rooms, lighting that enables recognition of faces is essentialto determine who belongs in the space and who doesn’t; who is perceived as safe and who maypresent a danger. Corridors tend to be dark in many multi-occupancy dwellings. A minimummaintained illuminance of 100 lx should be provided at floor level.

18.5 Lighting equipment

18.5.1 Light sources Most general-purpose light sources can be used for security lighting (see Chapter 3). HIDlamps tend to be used for all-night security lighting because they have high luminous efficaciesand long lives, they are unaffected by the ambient operating temperature and are available in awide range of lumen ratings, colours and wattages.


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gAgainst these advantages, they require bulkier luminaires, control of light output is moredifficult, initial cost is higher and mounting may be more complex. These disadvantages can beoffset by the benefits of needing far fewer fixture locations or mounting multiple luminaires ina single location.

The longer run-up and restrike times of HID lamps make them unsuitable when the lighting isonly energised when an intruder is detected or a brief period of darkness occurring in the eventof a power failure is unacceptable. In these situations, an incandescent or fluorescent lightsource is preferred.

18.5.2 LuminairesThe selection of the luminaire will be based on the light source to be used, the desiredluminous intensity distribution, aesthetics and the degree to which the luminaire will beexposed to the environment. Environmental factors to be considered include exposure to wind,rain and salt; temperature extremes; luminaire mounting location; and the level of vulnerabilityof the luminaire to damage by attack.

Any fixture mounted in an area that will be exposed to the weather should have an appropriateinternational protection (IP) rating (see Table 4.10).

Luminaires that are located in areas that are not temperature controlled may need specialcomponents depending on the light source used. Fluorescent light sources are most affected byambient temperature extremes.

Any luminaire mounted on a ceiling or wall less than 3 m above the ground is likely to be thesubject of vandalism. Vandal resistant lighting should be considered in these applications. Avandal resistant luminaire should incorporate the following features:

The base of the luminaire should be structurally designed, i.e. have a step or flanged base, and be solidly mounted to the building structure or mounting accessory. An electrical junction box should never be used as the sole luminaire support in a security lighting installation.

The lens or diffuser of the luminaire should be of a one-piece wraparound, injection moulded construction using ultraviolet (UV) stabilised polycarbonate.

Exposed hardware, such as that needed to secure the lens to the body of the luminaire, should be tamperproof.

Light sources and sockets should be protected against mechanical shock and never located close to the interior wall of the lens.

The luminaire should have the ability to withstand repeated blows from a heavy rubber mallet or hammer.

18.5.3 Lighting columns The higher luminaires are mounted from the ground, the fewer columns and luminaires willbe required to light a given area and the less likelihood of vandalism. As column heights arereduced, more columns with lower wattage luminaires are required to avoid glare and non-uniform lighting patterns. Steel and concrete columns are most resistant to attack.


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Aluminum and fibreglass columns can be damaged by forced oscillation. Columns made ofthese materials should be avoided in areas where vandalism is prevalent.

18.5.4 Lighting controlsSecurity lighting should always be controlled automatically; activation should never be madethe responsibility of an individual. System design should consider the possibility of poweroutages and lamp failure. Redundancy should be considered when assigning luminaires to‘zones’ of control so that the failure of one luminaire does not leave a large area unlit.

HID systems should be designed to be energised prior to darkness by a time suitable for therun-up period of the lamp. Lighting controls should be designed to energise the lighting systemwhen the ambient natural light level is 1.6 times the maintained mean illuminance design valueor 15 lx, whichever is higher. This will ensure that designed illuminances will be met duringdusk as well as after dark.

Types of automatic controls suitable for security lighting operation include time switches, photo-cells, dimmers and motion detectors.

Time switches: these are generally used to control large areas from one location, such as shoppingcentre car parks. Astronomical time switches can be programmed to adjust on-off times withthe changes of season. These types of switches can be quite expensive, and still may not be ableto readjust by themselves if darkness is hastened by cloud cover. All time switches shouldinclude a battery back-up.

Photocontrols: these are used to control individual or small groups of luminaires on circuits thatare always energised. They can be designed to automatically energise luminaires during darkperiods regardless of time of day. They have the added advantage of not needing to be re-setafter power outages or at the changes to and from daylight savings time. Photocontrols shouldnot be mounted where the light sensing area is accessible to flashlight or vehicle headlight beams.

Dimmers: these can be used to reduce illumination and power demand by approximately 50percent during low traffic periods in such applications as office car parks during working hoursor shopping centre car parks late at night. By dimming all luminaires, the entire area remainsuniformly illuminated. This contrasts with the ‘spotty’ appearance commonly caused when halfof the luminaires are switched off to save electricity. Dimmable fluorescent and HID luminairesrequire special ballasts. Dimmed HID sources may not have the same colour characteristics aswhen they are operated at 100 percent light output. This can have implications for camerasurveillance as well as the ambiance of the space.

Motion detectors: these are used to switch on specific luminaires when motion is detected.Motion detectors can employ infrared or ultrasonic technology. Passive infrared detectors arethe predominant choice outdoors, due to the sensitivity of ultrasonic detectors to movementcaused by wind. The designer should review the coverage pattern with the manufacturer’s datato determine suitability for the application. Due to the run-up time of HID light sources,motion detectors should only be used with incandescent and fluorescent light sources.

18.5.5 MaintenanceNo security lighting system can remain effective without regularly scheduled maintenance. A planned maintenance program should include: Immediate replacement of failed lamps, repair or replacement of vandalised luminaires, regular cleaning and cutting back of anyencroaching vegetation.


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Chapter 19: Sports lighting

19.1 Functions of lighting for sports

The function of lighting for sports is primarily to make what is going on highly visible toparticipants and spectators, without discomfort to either. Sports can be played both outdoorsand indoors. Outdoor facilities range from large multi-use stadia to village tennis courts. Indoorfacilities range from multi-use sports halls to single-use swimming pools. Some sports, such asfootball, rugby, cricket, tennis and golf are big business while others, such as archery andcurling are specialist interests. Big businesses often depend on sales of television rights for asignificant proportion of their income. In such circumstances, the lighting also has to serve theneeds of television transmission so that the spectators watching via a screen can see what isgoing on. The guidance given here is for the most popular sports. Detailed guidance on lightingfor a wider range of sports can be obtained from the SLL Lighting Guide 4: Sports lighting.The governing bodies of some sports make their own lighting recommendations. Theserecommendations may exceed those given here. The recommendations given here, and in SLL Lighting Guide 4: Sports lighting, should be treated as minima.


Sports facilities come in many different forms. They can be private or public. They can be large or small. They can cater for thousands of spectators or for the players alone. The sportsthemselves can call for fine discrimination of rapidly moving targets or simply the ability to see a stationary target in a known position. The directions of view can vary widely frompredominantly upward, as in badminton, to predominantly downward as in snooker, andanywhere in between, as in football. Despite the variability faced by the designer of sportslighting, the objectives are the same everywhere. They are:

to facilitate a high level of performance by the players

to enable spectators, both present and remote, to see clearly what is going on

to enable the sport to be played after dark

to create a safe environment for both players and spectators

to create a comfortable visual environment for both players and spectators.

To meet these objectives it is necessary to consider many aspects of the situation. Those listedbelow are relevant to all sports lighting applications.

19.2.1 Standard of play and viewing distanceAny sport can be played at different levels, from the completely professional to the grossamateur. Providing lighting suitable for the gross amateur in a facility used by the completelyprofessional is a disservice to the sport. Equally, providing the lighting necessary for theprofessional in a facility used by the gross amateur is a waste of money. Therefore, sportslighting recommendations are divided into three classes according to the players’ level of skill.

Another factor that influences sports lighting recommendations are the distances from which spectators have to view the sport. The greater the distance from which spectators view the activity and the finer the detail that has to be seen, the higher the class of lighting recommended.


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The three classes of lighting recommendations are:

Lighting class IInternational and national competitionLarge numbers of spectators with long viewing distancesTop level supervised training

Lighting class IIMid-level competition, principal local clubs and county regional competitionMedium numbers of spectators with medium viewing distancesHigh level supervised training

Lighting class III Low-level competition; local or small club competitionMinimal or no spectator provisionGeneral training; school sports or recreational activities.

The nature of some sports, particularly the speed with which visual information needs to beprocessed, means there is some overlap in the lighting recommendations for different sports atdifferent levels.

19.2.2 Playing areaThe nominal playing area is the marked out area of the ‘court’ or ‘pitch’ for the sport. However,for some sports, such as tennis, there is a larger area surrounding the nominal playing area withinwhich play may occur. Further, even when play is confined to the nominal playing area, there is asurrounding area that a player may enter, e.g. the area around a football pitch. The total area to belit includes the actual playing area and the safety zone around the actual playing area. Advice onnominal playing areas and total areas for different sports can be obtained from the governingbodies of the sports and, for some sports, from SLL Lighting Guide 4: Sports lighting.

19.2.3 LuminairesLuminaires used to light some sports facilities, such as sports halls, are at risk of damage fromflying objects. To minimise this risk, luminaires should be located outside the main activity zoneand adequately protected by nets, wire mesh etc. Further, luminaires and the associatedprotection should be designed so as not to contain any traps for balls, shuttlecocks etc.

Luminaires used in swimming pools may be subject to a corrosive atmosphere. Careful selectionof luminaires is necessary to minimise this problem.

19.2.4 TelevisionTelevision cameras cannot match the human eye neither for its sensitivity nor for its ability toadjust rapidly to sudden changes in luminance and colour. This means that where televisioncameras are regularly used at a sports facility, the lighting design needs to be more stringent.

The illuminance required for different sports will depend on the type and sensitivity of thecamera, lens angle and speed of play. For classification purposes, sports are divided into threegroups, A, B and C (see SLL Lighting Guide 4: Sports lighting for the group appropriate forspecific sports). For each group, a range of minimum maintained vertical illuminances is given,the value chosen for each sport depending on the maximum shooting distance (Figure 19.1).


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Figure 19.1 For each group, a rangeof minimum maintainedvertical illuminances isgiven, the value chosenfor each sport dependingon the maximumshooting distance

While the average illuminance is an important metric, other metrics of equal importance to sportslighting where TV cameras are to be used are those concerned with illuminance uniformity.There are five such metrics. They are as follows.

The ratio of mean horizontal and mean vertical plane illuminances should be between 0.5 and 2.0, inclusive.

On planes facing a sideline bordering a main camera area or facing a fixed camera position, the vertical illuminance uniformity ratio (minimum/maximum) should be equal to or greater than 0.4.

At a single point on the four planes facing the sides of a playing area, the vertical illuminance uniformity ratio (minimum /maximum) should be equal to or greater than 0.3.

The horizontal illuminance ratio (minimum /maximum) should be equal to orgreater than 0.5.

On large playing fields, such as football pitches, the maximum gradient in horizontal illuminance should not be greater than 25 percent every 5 m.

As for light source colour properties where television is used, for outdoor facilities the correlatedcolour temperature of the light should be in the range 4,000 K to 6,500 K. Where there is littlecontribution from daylight, the correlated colour temperature of the lighting can be within therange 3,000 K to 6,500 K. For both outdoor and indoor facilities, the CIE general colourrendering index of the light source used should be greater than 65 and preferably have aminimum value of 80. Further advice on the lighting of sports events for television broadcastingcan be found in CIE Publication 169-2005.

19.2.5 Coping with power failuresEmergency lighting is required to cope with power failures. This can take two basic forms,emergency escape lighting and standby lighting. Emergency escape lighting is designed to enablepeople to exit a building quickly, without panic. The requirements for emergency escape lightingare given in Chapter 8 of this Handbook and in SLL Lighting Guide 12: Emergency lighting designguide. Standby lighting for sports facilities can also take two forms. The first is safety lighting,which is designed to ensure that the event can be stopped without injury to the players. Thesecond is continuation lighting, which is designed to enable the event to continue.

C

B

A

1600

1400

1200

1000

800

600

400

200

0

0 25 50 75 100 125 150 175 200

Shooting distance in metres

Ev (lx)


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Safety lighting is not necessary in all sports, only those where rapid motion is likely to beoccurring at the instant of power failure, for example gymnastics, ice hockey and horse racing.The illuminance requirements for safety lighting are usually specified as a percentage of thenormal illuminance recommendation for a set number of seconds. The safety lightingrequirements for specific sports are given in Section 19.3.

Continuation lighting requires the provision of a secondary lighting system powered from agenerator or a central battery. A typical system would consist of a number of luminairesconnected to both the mains supply and to a change-over switch that can detect the power failureand connect the luminaire to the generator or battery unit. If the light source being used is notincandescent or fluorescent, it will also be necessary to use a hot-restrike system. If a generator isto power the secondary lighting system it may also be necessary to have a battery system toprovide instant power to cover the run-up time of the generator which can be as long as 20seconds. For continuation lighting to be successful, it should provide illuminances at least to thelevel of those provided for Class III of that sport (see Section 19.3).

19.2.6 Obtrusive lightBecause of the high illuminances required, outdoor sports facilities are a common source of complaints about light pollution. Such complaints can take two forms, light trespass and skyglow.

Complaints about light trespass are usually made by the owners of adjacent properties. Criteriato determine if such complaints are justified are given in Section 6.2.9. If the complaints arejustified, the source of complaint can often be removed by carefully aiming of the lighting or bybespoke shielding of the luminaires to prevent any direct light from the installation reaching thewindows of the complainant (Figure 19.2). Light pollution in the form of light trespass is arecognised statutory nuisance under the Clean Neighbourhoods and Environment Act 2005.

Figure 19.2Special shielding of floodlights ona tennis court designed to avoidlight trespass on nearby properties

Complaints about sky glow are more likely to be made by pressure groups that object to the use of the facilities at night. It is not the job of lighting designers to justify the use of sports facilities at night but it is their job to minimise the amount of sky glow. This can be done by the carefulselection and aiming of luminaires and the advocacy of a curfew system for the use of the lighting.Advice on designing outdoor lighting with minimum sky glow is given in the Society of Light andLighting Factfile 7, Environmental considerations for exterior lighting and in the references CIEPublication 150-2003 and ILE Guidance notes on the reduction of obtrusive light.


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The following tables summarise the recommendations for the lighting of sports facilities in the different lighting classes. The recommendations are given for sports of majority interest. Recommendations for lighting sports of minority interest are available in the SLL Lighting Guide 4: Sports lighting. The following notes are essential for interpreting the recommendations.

The horizontal and vertical illuminances given are both minimum maintained average values.Horizontal illuminance is for the playing surface. Vertical illuminance is usually on a specifiedplane at a given height above the ground. Methods for measuring or calculating the meanilluminance are given in SLL Lighting Guide 4: Sports lighting.

Illuminance uniformity is the ratio of minimum illuminance to the mean illuminance over theactual playing area. Methods for measuring or calculating the illuminance uniformity are givenin SLL Lighting Guide 4: Sports lighting.

For indoor facilities, glare control is achieved by specifying a maximum unified glare rating(UGR). For outdoor facilities, glare control is achieved by specifying a maximum glare rating(see Section 17.3.2 and CIE Publication 112-1994).

19.3.1 AthleticsAthletics can take place outdoors in a stadium or indoors in an arena. The lighting in both sortsof facility should be adequate for both field and track events. Where sports involving flyingmissiles such as the discus, javelin and hammer are to take place, the lighting should ensure themissile is visible throughout its flight. For the track, the vertical illuminance at the finishing lineshould be at least 1000 lx to enable the photo-finish equipment to operate. For class III outdoortracks, the recommended horizontal illuminance can be reduced to 50 lx for jogging. Athleticsfalls into TV group A.

Table 19.1 Lighting recommendations for indoor athletics

Class

I

II

III


500

300

200

Illuminanceuniformity

0.7

0.6

0.5

Colour rendering index

60

60

20

Table 19.2 Lighting recommendations for outdoor athletics

Class

I

II

III


500

200

100


0.7

0.7

0.5


60

60

20

Glarerating

50

50

55


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19.3.2 BowlsBowls requires the players to be able to see the jack, the lie of the woods around the jack andthe run of a live wood. To achieve this, a high level of illuminance uniformity is necessary andglare needs to controlled. An illuminance gradient of not more than 5 percent per metre isrecommended. Bowls falls into TV group A.

For indoor bowls, the usual lighting approach is to use fluorescent luminaires mounted at least3 m above the floor, ideally on either side of the lanes (Figure 19.3). Glare is controlled by thechoice of luminaire and ensuring that the reflectances of the walls and ceiling are at least 0.4and 0.6 respectively.

Figure 19.3For indoor bowls, the usuallighting approach is to usefluorescent luminaires mounted atleast 3 m above the floor, ideallyon either side of the lanes

For outdoor bowls, the usual lighting system is floodlights mounted at the corners of the green.Light should reach all parts of the green from at least two directions if good modelling is to beprovided. Glare is controlled by careful selection of mounting height and aiming of floodlights.

Table 19.3 Lighting recommendations for indoor bowls

Class

I

II

III


500

500

300


0.8

0.8

0.5


60

60

20

Table 19.4 Lighting recommendations for outdoor bowls

Class

I

II

III


200

200

100


0.7

0.7

0.7


60

60

20

Glarerating

50

50

55


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19.3.3 CricketCricket is played with a hard ball delivered at high speed. The bowler needs to have a clear viewof the pitch and wicket. The batsman needs to have a clear view of the bowler’s action and run-up. The fielders need to be able to see the flight of the ball. To meet these objectives more lightis usually provided more uniformly in the square near the wicket than in the outfield and glareneeds to be limited as far as possible. Cricket is in TV group C.

For indoor cricket, which can take the form of games and training nets, the usual lightingapproach is to use fluorescent luminaires, taking care to minimise glare. The luminaires areprotected by nets hung at least 1 m below the luminaires, ideally on either side of the lanes(Figure 19.4).

Figure 19.4Lighting for indoor cricket

For outdoor cricket, the usual lighting system uses high-mounted floodlights. Light shouldreach all parts of the field from at least two directions. Glare is controlled by careful selection ofmounting height and aiming of floodlights. A white ball is often used to after dark to give abetter contrast against the night sky.

Table 19.5 Lighting recommendations for indoor cricket

Class

I

II

III


750

500

300


0.7

0.7

0.7


60

60

20

Class

I

II

III


1500

1000

750


0.8

0.8

0.8


60

60

20

Table 19.6 Lighting recommendations for indoor cricket training nets


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Table 19.7 Lighting recommendations for outdoor cricket

Class

I

II

III

Horizontalilluminance on

wicket square (lx)

750

500

300

Illuminanceuniformityon wicket

square

0.7

0.7

0.5

Horizontalilluminance on

outfield (lx)

500

300

200

Horizontalilluminanceuniformityon outfield

0.5

0.5

0.3

Glarerating

50

50

55

Colourrendering

index

60

60

20

19.3.4 Five-a-side football (indoor)In this sport, players must be able to follow the movement of both the ball and other players.This sport usually takes place in multi-use sports halls (Figure 19.5). The lighting usuallyconsists of a regular array of ceiling mounted luminaires spaced to provide the necessaryilluminance uniformity. The luminaires need to be protected from the ball. Glare can bereduced by ensuring the ceiling has a reflectance in the range 0.6 to 0.9. This sport is in TV group B.

Figure 19.5For five-a-side football, thelighting usually consists of aregular array of ceiling mountedluminaires spaced to provide thenecessary illuminance uniformity

Class

I

II

III


750

500

200


0.7

0.7

0.5


60

60

20

Table 19.8 Lighting recommendations for indoor five-a-side football

19.3.5 Fitness trainingFitness training involves the use of equipment such as weights, treadmills and rowingmachines. The purpose of the lighting is to allow safe operation of the equipment and toprovide a comfortable environment. Usually, the lighting consists of a regular array of ceilingmounted luminaires. The reflectance of the ceiling should 0.6 or more so as to buffer thebrightness of the luminaires viewed directly by someone looking upwards.


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Class

I, II and III


500


0.8


60

Table 19.9 Lighting recommendations for fitness training

19.3.6 Football (Association, Gaelic and American)Football involves the rapid passage of a ball combined with physical contact between players. Athigh levels, these sports attract large numbers of spectators which means that attention shouldbe paid to emergency lighting and the lighting requirements may be specified by UEFA orFIFA. For lower classes, football is in TV group B. The purpose of the general lighting is toprovide uniform illumination of the pitch, with good modelling of players and withoutshadows or glare to players or spectators. This purpose can be met by a number of differentapproaches, from pole-mounted floodlights to continuous lines of floodlights mounted on theroofs of grandstands. If the former approach is used, it is important to note that for Associationand Gaelic football, lighting masts should not be located within 10 degrees of the goal line axis.

Table 19.10 Lighting recommendations for Association, Gaelic and American football

Class

I

II

III


500

200

75


0.7

0.6

0.5

Glare rating

50

50

55

Colourrendering index

60

60

20

19.3.7 Lawn tennis The main visual requirements in tennis are for the players, match officials and spectators to seethe ball, player and court clearly. The flight of the ball indoors will be seen easily if the ball isseen against a dark background. The reflectance of any vertical fabrics or surfaces surroundingthe court should not be greater than 0.5. The ceiling above the court and extending 3 m behindthe base lines should be kept free from luminaires. Typical lighting systems for indoor courtsuse luminaires that are mounted parallel to the sidelines, extend beyond the baselines and areoutside the court area. For outdoor courts, sharp cutoff floodlights mounted on columns to thesides of the court are the usual choice. The choice of light source depends on the materialforming the court. For both indoor and outdoor courts, the Lawn Tennis Association hasspecific illuminance requirements for the total area and the principal area (see Section 19.2.2).Lawn tennis is in TV group B.

Table 19.11 Lighting recommendations for tennis (indoor)

Class

I

II

III


750

500

300


0.7

0.7

0.5


60

60

20


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I

II

III


500

300

200


0.7

0.7

0.6


60

60

20

Glarerating

50

50

55

Table 19.12 Lighting recommendations for tennis (outdoor)

19.3.8 Rugby (Union and League)Rugby involves the rapid passage of a ball combined with physical contact between players. Athigh levels, these sports attract large numbers of spectators, which means that attention shouldbe paid to emergency lighting. The purpose of the general lighting is to provide uniformillumination of the whole pitch, with good modelling of players and without shadows or glareto players or spectators. This purpose can be met by a number of different approaches, frompole-mounted floodlights to continuous lines of floodlights mounted on the roofs ofgrandstands. If pole-mounted floodlights are used, they should be positioned so that they donot obstruct the view of spectators. If floodlights mounted on the roofs of stands are used careshould be taken that shadows are not cast onto the pitch. For rugby, it is permissible to placefloodlights in line with the try line. Rugby is in TV group B.

Table 19.13 Lighting recommendations for rugby (union and league)

Class

I

II

III


500

200

75


0.7

0.6

0.5

Glare rating

50

50

55

Colourrendering index

60

60

20

19.3.9 SwimmingSwimming is not a sport that requires the participants to undertake difficult visual tasks. Thepurpose of the lighting of swimming pools is to ensure safety and to provide a pleasantambience. The safety requirement will be met by lighting that provides sufficient illuminancewith careful control of reflections from the water surface (see Section 19.4.4). To ensure safetyin the event of a power failure, safety lighting that produces 5 percent of the recommendedilluminance for at least 30 seconds should be provided. Diving areas require specialconsideration with regard to glare and modelling. Swimming is in TV group A.

Table 19.14 Lighting recommendations for swimming in indoor and outdoor pools

Class

I

II

III


500

300

200

Horizontal illuminance uniformity

0.7

0.7

0.5


60

60

20

Horizontal/verticalilluminance ratio

for diving area

50

50

55


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19.4 Lighting in large facilities

19.4.1 Multi-use sports hallsAs its name implies, a multi-use sports hall is an indoor facility where many different sports areplayed, sometimes simultaneously and where there is only limited provision for spectators. Theessential characteristics of the lighting of multi-use sports halls are enough illuminanceprovided uniformly without glare. Given the multiple uses of the sports hall, this implies someflexibility in the lighting through switching (Figure 19.6). The usual design approach is to firstidentify the sports that will need to be accommodated and the potential for non-sporting uses.The lighting requirements for each sport need to be established and the relative importance ofthe sports listed. The lighting approach most commonly used is a ceiling-mounted regular arraygeneral lighting system with switching arrangements for different activities, levels of play orsimultaneous use. With such a system, the illuminance on the walls and ceiling should be atleast 50 percent and 30 percent respectively of the illuminance on the playing area. It isimportant for the layout of the playing areas and the type and layout of the lighting to beplanned together. Where the different sports have been prioritised, the lighting should bedesigned to meet the requirements of the highest priority sport while ensuring that, as far aspossible, all other activities are catered for. Where there is limited information on expectedusage or badminton is one of the sports to be catered for, the lighting should be designed to suitthe layout of the badminton courts. Badminton has the most exacting visual requirements ofthe sports played in multi-use sports halls and a lighting scheme that satisfies the requirementsfor badminton and is matched to the court layouts will often cater adequately for a wide rangeof other sports.

Figure 19.6Lighting of a multi-sport hall

19.4.2 Small sports stadiaA small sports stadium is an outdoor sports ground consisting of a central field area surroundedby an athletics track and sometimes a cycle track. The central area may be used for fieldathletics and other sports such as football, rugby and hockey. The spectator capacity is typicallyless then 5,000, usually in a grandstand located on one side. The sports taking place in smallsports stadia are usually at the level of lighting classes II and III. Floodlights mounted on mastseither at the four corners of the stadium or located around the perimeter of the track, except infront of the grandstand, are the most common approaches. Floodlights can also be mounted onthe grandstand provided care is taken to avoid casting shadows onto the track and central area.Care should also be taken to avoid glare to participants in field events involving throwing and jumping.


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19.4.3 Indoor arenasIndoor arenas are usually built to cater for a variety of events, some sporting and some not.Permanent spectator seating is arranged around the event floor with temporary seating beingplaced on the floor as required. Given the variety of uses, the temptation is to design thelighting to meet all possibilities but experience suggests that the best approach is to providepermanent lighting for the main sports event and for setting up, using temporary lighting forany specific event that calls for something different (Figure 19.7).

Figure 19.7Lighting of an indoor arena

The usual approach for lighting the sports area of indoor arenas is to use floodlights similar tothose used for outdoor stadia. The design is built up from overlapping beams until the wholearea is covered. Higher illuminances are created by adding more layers. Some flexibility isneeded to cover different sports that use different parts of the sport area. This can be achievedby switching different layers of light.

Given the different uses to which an arena may be put, there will be a need for frequentchanges of the floor. This requires a separate lighting installation for setting up, a lightinginstallation that provides 100 lx on the floor. If the set-up lighting is also used as house lighting,a light source with a CIE general colour rendering index of 80 should be used. If the set-uplighting is not used as house lighting, a separate lighting installation will be needed over thepermanent seating providing a similar illuminance to the set-up lighting. This lighting mayneed to be dimmed during the events.

19.4.4 Swimming poolsSwimming pools vary widely in design but they all have a problem with high luminancereflections from the water surface. This is important because such reflections tend to maskwhat is happening beneath the water. The reflectance of water increases rapidly as the angle ofincidence exceeds 70 degrees. In principle, it should be easy to eliminate high luminancereflections by ensuring that the angle of incidence is below 70 degrees. However, movement ofthe water means that the angle of incidence can vary dramatically.

For indoor pools, a good approach is to use indirect lighting designed to ensure that there areno high luminances to be reflected, apart from any views of the sky and sun through windowsor skylights (Figure 19.8). There are two factors that influence the location of indirectluminaires. The first is the need to maintain the luminaires. Luminaires should not be locatedover the pool unless they are accessible from catwalks or from behind the ceiling. The second isthe need to avoid glare to spectators and pool attendants, both of whom may be sitting someheight above the water. Luminaires in indoor pools should be constructed to withstand hightemperatures, humidity and corrosion. A minimum IP number of IP54 is recommended.


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Figure 19.8Lighting of a swimming pool

For outdoor pools, lighting is usually provided by floodlights mounted on masts around thepool. The mounting height should be such that the angle of incidence on the far side of thepool is more than 50 degrees and preferably 60 degrees.

Both indoor and outdoor pools may have underwater lighting. This reduces the effect onvisibility of high luminance reflections from the water surface. Underwater lighting takes twoforms, dry and wet. Dry underwater lighting has the luminaires behind watertight portholes.Wet underwater lighting has the luminaires in the water but with cables long enough so thatthey can be serviced from the poolside. Narrow beam floodlights are used for underwaterlighting, with the beam axis aimed approximately 10 degrees above the horizontal. Almost total internal reflection takes place at the surface of the water so there is no risk of glare to surface swimmers, judges or spectators. Underwater lighting should not be used for races or for water polo.


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Chapter 20: Lighting performance verification

20.1 The need for performance verification

Verifying the performance of a lighting installation is desirable for three reasons. First, anyonewho has paid for a new lighting installation should be interested to know if they have got whatthey paid for. Second, anyone who has designed a lighting installation and has seen it installedshould be concerned with how well the actual installation matches what was expected from thedesign. Discrepancies between the design and reality can indicate problems with the designprocess or with the data used in the design. Third, lighting installations change as they age (seeChapter 21). Light sources tend to produce less light with increasing hours of use. Luminairesemit less light and can change their light distribution as they get dirty. The amount of inter-reflected light can change as surface reflectances change. For applications where minimumstandards of lighting are specified, being able to measure the current performance of a lightinginstallation is desirable to schedule maintenance correctly.

The verification of the performance of a lighting installation requires a field survey. Such a surveyrequires decisions about the relevant operating conditions, the use of photometric instrumentsand the selection of an appropriate measurement procedure.

20.2 Relevant operating conditions

It is essential when making field measurements to keep a complete and accurate record of thestate of the lighting installation and the interior in general at the time the measurements aremade. Particular attention should be given to the lamp type and age, the level and stability of thesupply voltage, the state of maintenance of the lamps and luminaires, the surface reflectances, thedegree of obstruction and any other factors that could influence the measurement. Photographsof the interior are a valuable supplement to a written record.

Before carrying out a field survey, it is necessary to decide on the lighting conditions that are ofinterest. For example, is daylight to be admitted and, if it is, what type of control is to be used?Are the measurements to be concerned with average values over the whole interior or only overindividual workplaces? Should the measurements around the workplace be taken with the peoplepresent, etc? It is also necessary to identify the appropriate measurement plane; horizontal andvertical and at what height or orientation.

Before starting to take measurements it is first necessary to ensure that the lamps have been burntfor at least 100 hours. If this has been done, then the first step in measurement is to stabilise theperformance of the lamps, luminaires and instrumentation. The time required to stabilise thelight output of an installation depends on the type of light source and luminaire. Installationsusing discharge lamps, including tubular fluorescent, require at least 20 min, and ideally onehour, to stabilise before measurements are made.

To stabilise the reading of some instruments the photocell should be exposed to the approximateilluminances to be measured for about 5 min before making the first measurement.

Daylight is rarely stable and hence the illuminance and luminance it produces can rapidly varyover a very large range. For this reason when measurements of the electric lighting installationalone are required, daylight must be excluded from the interior or the measurements must bemade after dark.


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20.3 Instrumentation

Field measurements of lighting are usually undertaken with two basic instruments, anilluminance meter and a luminance meter.

20.3.1 Illuminance metersIlluminance meters usually consist of a selenium or silicon photovoltaic cell connected directly,or indirectly via an amplifier, to an analogue or digital display (Figure 20.1). The quality of anilluminance meter is determined by a number of factors including calibration uncertainty, non-linearity, spectral correction error, cosine correction error, range change error and temperaturechange error. All these errors are discussed in detail in BS 667: Specification for illuminance meters.This standard defines two types of meter, type L mainly designed for laboratory use and type Fdesigned for field use. The total uncertainty for a type L meter is ±4% and ±6% for a type Fmeter. These error limits assume the measurement of nominally white light. Measurements ofhighly coloured light sources, such as some light emitting diodes, may show much greatererrors because of the poor fit of the spectral sensitivity of the meter to the CIE StandardPhotopic Observer at particular wavelengths.

Figure 20.1An illuminance meter

Illuminance meters are available for measuring illuminance from 0.1 lux to 100,000 lux, i.e.from emergency lighting conditions to daylight conditions. It is important to use anilluminance meter with a range matched to the illuminances to be measured.

20.3.2 Luminance metersA luminance meter consists of an imaging system, a photoreceptor, and a display (Figure 20.2).The optical imaging system is used to form an image of the object of interest on thephotoreceptor. The photoreceptor produces a signal that is dependent on the average luminanceof the image it receives. The object of interest must be in focus and fill the photoreceptoraperture in order to obtain valid readings. This signal is amplified and displayed in eitheranalogue or digital form. By changing the imaging system it is possible to alter the field of viewof the photoreceptor to give different areas of measurement. The photoreceptors used inluminance meters may be photovoltaic cells or photomultiplier tubes. The photovoltaic cells, asin illuminance meters, need to be colour corrected and used with associated circuitry to give alinear response and operate acceptably over a range of ambient temperature.


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Figure 20.2A luminance meter

BS 7920: Specification for luminance meters discusses in detail the uncertainties that luminance metersmay be subject to and specifies limits for the uncertainties for two classes of luminance meter. Thetwo types of meter are type L, laboratory meters and type F, field meters. A meter that just meetsthe standard would have a best measurement capability of ±5% (Type L) or ±7% (Type F). Theuncertainties for measurements of highly coloured light sources may be greater.

Luminance meters are available which provide measurements over a range of 10-4 to 108 cd/m2 forareas varying from a few seconds of arc to several degrees. It is important to use a luminance meterwith appropriate sensitivity and measurement area for the application.

20.4 Methods of measurement

The lighting recommendations given in this Handbook, the SLL Code for lighting and the SLLLighting Guides usually involve some combination of average illuminance; some measure ofilluminance variation, either illuminance diversity or illuminance uniformity; some measure ofglare limitation which can be a maximum luminance, a unified glare rating (UGR) for interiorlighting or a glare rating (GR) for exterior lighting; and a colour rendering index (CRI). Of these,only the average illuminance, illuminance diversity, illuminance uniformity and surface luminancecan be measured in a field survey. Both UGR and GR have to be calculated for given viewingpositions and directions, and CRI is a property of the light source.

20.4.1 Average illuminance The average illuminance over an interior is usually measured to check if an installation hasachieved its design specification. For design calculations using computers it is practical to obtain aprint-out of illuminance over a large number of closely spaced grid points. With sitemeasurements, for logistical reasons the aim must be to obtain acceptably accurate results from aminimum number of points. To do this, the following procedures are recommended after theinstallation has been operating for an appropriate time at the design supply voltage. For dischargelamps this time is 100 hours, but it will be less for incandescent lamps.

20.4.2 Interior lightingFor interior lighting, there are two possible methods of measurement of average illuminance. Thefirst is based on a full grid of measurement points over the working plane or specific task areas, asrequired. The same grid may be used in the measurement of illuminance variation. The second is atwo-line method of measurement for average illuminance that may be used for a limited range of installations.


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Full grid of measurement points When this method is applied to an interior lighting installation, the interior is divided into anumber of equal size cells that should be as square as possible.

The illuminance at the centre of each cell is measured and the mean value for all the cells iscalculated. This gives an estimate of the average illuminance. The accuracy of the estimatedepends on the number of cells and the variation of illuminance. Table 20.1 relates the roomindex (RI) to the number of cells necessary to give an error of less than 10%; the data in Table20.1 are valid for spacing-to-height ratios up to 1.5:1.

Table 20.1 Minimum number of cells to form a full grid when measuring averageilluminance in an interior

Room index (RI)

Number of cells

RI < 1

9

1 > RI < 2

16

2 > RI < 3

25

RI >3

36

The only limitation on the use of the above is when the grid of cells coincides with the grid oflighting points; large errors are then possible and more cells than the number given should beused. The numbers of cells suggested are minima, and it may be necessary to increase theirnumber to obtain a symmetrical grid to suit a particular room shape. The following examplesillustrate the use of the method:

(a) An interior measuring 20 m × 20 m and with luminaires mounted 4 m above the working plane has a room index of 2.5. A minimum of 25 cells is therefore required, i.e. a 5 × 5 grid spaced at 4 m × 4 m.

(b) If the room measures 20 m × 33 m with the luminaires mounted at the same height, the room index of 3.1 indicates that a minimum of 36 cells would suffice. To give a grid which is acceptably ‘square’, 40 cells could be used, spaced at 4 m × 4.125 m.

10 m

Figure 20.3An L-shaped room with thedistribution of cells requiredfor the measurement ofaverage illuminance

20 m

25 m

15 m


(c) Re-entrant room shapes may be divided into separate, smaller rectangular areas and the closest spacing arrived at by the above method applied to the whole room (Figure 20.3). Thus a room of 25 m × 20 m with a 10 m × 10 m re-entrant portion at one corner may be considered as two areas of 20 m x 15 m and 10 m × 10 m. For a luminaire mounting height of 3 m the larger area has a room index of 2.8, suggesting a minimum number of cells of 4 × 6 = 24 at a grid spacing of 3.75 m × 3.3 m. The smaller area has a room index of 1.7 indicating a minimum number of points as 16 at a spacing of 2.5 m × 2.5 m. A grid of pointsspaced at 2.5 m would be applicable to the whole space.

Illuminance measurements should be made at the centre of each cell, at the height of theworking plane, over the whole space or over the task area, as required. If the working plane isnot specified, measurements should be taken on a horizontal plane at 0.8 m above the floor. Aportable stand or tripod is useful to support the photocell at the required height and inclination.Care should be taken not to cast a shadow over the photocell when taking the readings.

Two-line method This method applies to rectangular interiors lit by a regular layout of ceiling-mountedluminaires that are installed at or below the manufacturers’ maximum spacing-to-height ratios.It is not suitable for measurement of average illuminance in non-uniform installations,installations with a mixture of mounting heights, other unconventional layouts or thoseconsisting of mixtures of different ceiling mounted luminaires or uplighters. In such cases thefull grid measurement method must be used.

In the two-line method, measurements are taken at evenly spaced intervals along twoperpendicular lines parallel to the two axes of the room. The spacing of the measurements maybe at any convenient distance but must not exceed the spacing of the cells calculated from Table20.1 and must include a reading at the intersection of the two lines. The intersection pointshould be chosen to avoid positions exactly below or midway between luminaires. The averageilluminances along the two lines of measurement are calculated. The overall averageilluminance of the installation (Eav) is then given by:

Eav = Ex Ey / Eis

where: Eis is the illuminance at the intersection point of the two linesEx is the average illuminance along line xEy is the average illuminance along line y

20.4.3 Exterior lightingFor exterior lighting installations, a full grid of measurements should be used. The cells areusually rectangular and the cell size in each axis should be a whole number. The illuminance ismeasured at the centre of each cell. The maximum cell size may be determined from theequation

p = 0.2 × 5log d

where: p = grid intervald = size of the longer reference axis

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Figure 20.4A full grid ofmeasurements shouldbe used for exteriorlighting installations

The number of cells in the larger dimension is given by the nearest odd whole number to thequotient of the size of the longer reference axis (d) and the grid interval (p). This result is thenused to calculate the nearest odd whole number of cells in the smaller dimension. In asymmetrical but localised situation, as on an athletics track, the larger dimension d is given byone quarter of the distance of the overall inner track limit (Figure 20.5).

For the special case of road lighting, further guidance on measurement procedures is given inILE Technical Report 28: Measurement of Road Lighting Performance on Site.

20.5 Measurement of illuminance variation

To confirm compliance with the recommendations on illuminance variation, measurements ofilluminances over the whole working plane are needed to calculate illuminance diversity andover task areas and their immediate surrounds to calculate illuminance uniformity.

20.5.1 Illuminance diversity For a wide range of commercial and industrial interiors where the visual task may be adverselyaffected by excessive variations in illuminance, the full grid measurement method should beused. This will provide a coarse grid of points over the whole working plane. Additionalmeasurements are then required, centred on selected points to check for local maximum andminimum illuminances. These additional measurements are made on a 3 × 3 grid of points atabout 1 m centres. In this procedure any measurement locations within 0.5 m of room walls orlarge fixed obstructions are ignored.

Figure 20.5 Calculation for an athletics track

p

d


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20.5.2 Illuminance uniformityTo measure illuminance uniformity, a 0.25 m square grid of measurement points is establishedover the task area and its immediate surround at a number of representative positions. Taskilluminance uniformity is assessed using the area-weighted arithmetic average of themeasurement points within each task area and the minimum grid point illuminance valuewithin that area. The lowest values of illuminance uniformity calculated from the measuredvalues at the selected positions is taken as representative of the whole installation.

For measurement in an unfurnished area where there is no information on the task area andimmediate surround dimensions, the grid should be applied to the whole working plane.

20.6 Luminance measurements

Luminance measurements are often made in response to complaints about glare. In thesecircumstances the conditions that are the subject of complaint should be established andluminance measurements made from the position of the people who are complaining. In thisway the source of the complaints may be identified. When measuring the luminance of lightsources or luminaires, the meter should be mounted on a tripod and it is essential that the areaof interest must fill the complete photoreceptor aperture of the meter. If a luminance meter isnot available, an estimate of the luminance of matte room surfaces can be obtained indirectly bymeasuring the reflectance of the surface and the illuminance (lux) on it and then calculating theluminance (cd/m2).

20.7 Measurement of reflectance

Sometimes it is necessary to measure the reflectance of a surface, e.g. to determine if thereflectance is outside the recommended range or to establish if the reflectance assumed in acalculation is reasonable. There are a number of ways to do this. One is to measure theilluminance falling on the surface and the luminance of the surface at the same point. Thereflectance is then given by the expression:

R =

where: R is the reflectance of the surface at the measurement pointE is the illuminance on the surface at the measurement point (lx)L is the luminance of the surface at the measurement point (cd/m2)

Another method is to use a luminance meter and a standard reflectance surface made frompressed barium sulphate or magnesium oxide. The luminances of the surface of interest and thestandard reflectance surface are measured at the same appropriate position. Then the reflectanceof the surface of interest is given by the expression:

R = Rs L1 / Ls

where: R is the reflectance of the surface of interestL1 is the luminance of the surface of interest (cd/m2)Ls is the luminance of the standard reflectance surface (cd/m2)Rs is the reflectance of the standard reflectance surface

E πL


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This method can also be used to obtain the luminance factor (or gloss factor) for non-mattesurfaces where local values of luminance, from defined viewing positions, are of interest. Thishas little or no relevance to the average value of the inter-reflected illuminance received on theworking plane or other room surfaces.

If a luminance meter is not available, then an approximate measure of the reflectance of asurface can be obtained by making a match between the surface of interest and a sample from arange of colour samples of known reflectance as described in SLL Lighting Guide 11: Surfacereflectance and colour.


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Chapter 21: Lighting maintenance21.1 The need for lighting maintenance

A lighting installation starts to deteriorate from the moment it is first switched on. Maintenancekeeps the performance of the system within the design limits and promotes safety and the efficientuse of energy. Maintenance includes replacement of failed or deteriorated lamps and control gear,the cleaning of luminaires and the cleaning and redecoration of room surfaces. Detailed advice onlighting maintenance can be found in CIE Publications 97-2005 and 154-2003.

21.2 Lamp replacement

There are two factors to be considered when determining the timing of lamp replacement, thechange in light output and the probability of lamp failure. The relative weight given to these twofactors depends on the light source. Mains and low voltage tungsten filament and tungsten-halogen lamps usually fail before the decline in light output becomes significant. Therefore thereplacement time for these lamps is determined by the probability of lamp failure alone. All otherelectric light sources show a significant reduction in light output before a large proportion fail. Forthese lamps, both the decline in light output and the probability of lamp failure are important indetermining the lamp replacement time.

For the majority of lighting installations, the most sensible procedure is to replace all the lamps atplanned intervals. This procedure, which is known as group replacement, has visual, electrical andfinancial advantages over the alternative of ‘spot replacement’, e.g. replacing individual lamps asthey fail. Visually, group replacement ensures that the installation maintains a uniform appearance.Electrically, group replacement reduces the risk of damage to the control gear caused by the faultyoperation of lamps nearing the end of their life. Financially, by having the lamp replacementcoincide with luminaire cleaning and doing both at a time when it will cause the minimum ofdisturbance, the cost of maintenance can be minimised. Group replacement is an appropriateprocedure for routine maintenance and the frequency with which the procedure is carried out willhave a direct bearing on the installed electrical load. However, in any large installation, a few lamps can be expected to fail prematurely. These lamps should be replaced promptly on anindividual basis.

For many installations the most economic time for group replacement is when the light output ofthe lamps has fallen below 80% of the initial value and the lamp failures are becoming significantto the loss of average illuminance. The latest time for group replacement is when the designed‘maintained illuminance’ has been reached.

As light source development proceeds there is a temptation to replace one light source withanother that is superficially similar but of higher luminous efficacy. However, it is essential toestablish that the replacement light source and the existing control gear are compatible physically,electrically and photometrically. Before replacing any discharge light source with another of adifferent type or the same type but from a different manufacturer, advice on compatibility shouldbe sought.

21.3 Cleaning luminaires

The rate at which dirt is deposited on and in a luminaire depends on the amount and compositionof the dirt in the atmosphere, and on the type of luminaire. Over the same period and in the samelocation, dust-proof (IP5X) and dust-tight (IP6X) luminaires and open reflectors with slots in thetop will collect less dirt than louvred luminaires with closed tops, or luminaires with unsealeddiffusers (see Sections 21.7 and 21.8).


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For particularly dirty atmospheres or where access is difficult, the best choice would be dust-proof or dust-tight luminaires, ventilated luminaires that are designed to use air currents tokeep them clean, or lamps with internal reflectors. Even the most protected luminaires, e.g.dust-tight luminaires, will collect dirt on their external surfaces. Therefore even theseluminaires will need cleaning regularly.

The appropriate cleaning interval for luminaires and the lamps they contain is a basic designdecision. The factors that need to be considered are the cost and convenience of cleaning at aparticular time and the illuminance at that time in relation to the design maintainedilluminance. As a general guide, luminaires should be cleaned at least once a year but for somelocations this will not be sufficient.

A wide range of materials is used in luminaires. Table 21.1 summarises the most suitablecleaning methods for different materials. Additionally, equipment manufacturers provide usefulinformation on the most appropriate cleaning methods, or guidance can be obtained fromspecialist cleaning product suppliers.

Table 21.1 Methods for cleaning materials used in luminaires

Materials

Anodized aluminium

Stainless steel

Galvanized steel,natural aluminium

Enamel paint finish, polyester

powder coat

Glass

Acrylic,polycarbonate, glass-polyester,

reinforced plastic

Cleaning methods

Surfaces should be cleaned with a non-abrasive cloth or sponge using a neutral detergent in warm water which does not leave

a residue and then allowed to air dry.

Ultrasonic cleaning techniques.

Severe staining or contamination should be removed first by metal polish.

Surfaces should be cleaned with a non-abrasive cloth or sponge usinga neutral detergent in warm water and then the surface dried with a

clean cloth, following the grain of brushed finishes where applicable.

Surface lustre may be restored by applying an oil-based cleaningcompound with a cloth and wiping off all surplus.

Surfaces should be cleaned with a neutral-based detergent and wiped dry.

Surfaces should be cleaned with a non-abrasive cloth or sponge using a neutral detergent in warm water and the surface dried with

a clean cloth. Solvent-based cleaners should not be used.

Surfaces should be cleaned with a non-abrasive cloth or sponge using a neutral detergent in warm water that does not leave a

residue, then wiped and allowed to air dry.

Remove loose dirt and dust with a vacuum cleaner. Surfaces shouldbe cleaned with a non-abrasive cloth or sponge using a neutral-baseddetergent that does not leave any residue, then rinsed and wiped dry

with warm water containing an anti-static solution. Solvent-basedcleaners should not be used under any circumstances.

Ultrasonic cleaning techniques.


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21.4 Room surface cleaning

All room surfaces should be cleaned and redecorated regularly if a dirty appearance and lightloss is to be avoided. Regular cleaning is particularly important where light reflected from theroom surfaces makes an important contribution to the lighting of the interior, e.g. wheredaylight from the side windows is used or where the electric lighting installation has a highindirect component such as uplighting (see Section 21.7).

21.5 Maintained illuminance

The illuminance recommendations in the SLL Code for lighting and in this Handbook are all given in terms of maintained illuminance. Maintained illuminance is defined as the averageilluminance over the reference surface at the time maintenance is carried out. In other words,maintained illuminance is the minimum illuminance that the lighting installation will produce,on that surface, during its life.

Using maintained illuminance for recommendations implies that the designer must obtain adecision from the client on the maintenance policy to be implemented throughout the life ofthe installation in order to determine the maintenance factor to be used in their calculations. Ifthis cannot be achieved, the designer must clearly state the assumed maintenance programmeused in the design calculations.

21.6 Designing for lighting maintenance

The maintenance requirements for a lighting installation must be considered at the designstage. Three aspects are particularly important:

The maintenance factor used in the calculation of the number of lamps and luminaires needed to provide the maintained illuminance. Maintenance factor is defined as the ratio of maintained illuminance to initial illuminance. The closer the maintenance factor is to unity, the smaller the number of lamps and luminaires that will be needed. This approach demands a commitment to regular and frequent maintenance. Unless this commitment is fulfilled the installation will not meet the recommended maintained illuminance during its life.

Practical access and handling. Good maintenance will only occur if access to the lighting installation is safe and easy, and the lighting equipment is straightforward to handle.

Equipment selection. The dirtier the operating environment, the more important it is to select equipment that is resistant to dirt deposition.

21.7 Determination of maintenance factor for interior lighting

The quantity used to take account of the planned maintenance schedule when designing alighting installation is the maintenance factor. The maintenance factor (MF) for an indoorlighting installation is a multiple of four factors:

MF = LLMF × LSF × LMF × RSMF

where: LLMF is the lamp lumen maintenance factorLSF is the lamp survival factorLMF is the luminaire maintenance factorRSMF is the room surface maintenance factor.


0.1

1

1

1

1

1

1

0.5

0.98

0.97

0.99

1

0.99

1

1.0

0.96

0.94

0.97

0.98

0.97

0.99

1.5

0.95

0.91

0.95

0.97

0.95

0.98

2

0.94

0.89

0.93

0.96

0.94

0.98

6

0.87

0.80

0.80

0.91

0.84

0.97

10

0.85

0.76

0.72

0.88

0.79

0.96

12

0.84

0.74

0.68

0.87

0.78

0.96

14

0.83

0.72

0.64

0.86

-

0.96

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21.7.1 Lamp lumen maintenance factor (LLMF) The luminous flux from all electric light sources reduces with time of operation. The rate ofdecline varies for different light sources so it is essential to consult manufacturers’ data. Fromsuch data it is possible to obtain the lamp lumen maintenance factor for a specific number ofhours of operation. The lamp lumen maintenance factor is the proportion of the initial lightoutput that is produced after a specified time. Where the decline in light output is regular,LLMF may be quoted as a percentage reduction per thousand hours of operation.

Manufacturers’ data will normally be based on British Standards test procedures which specifythe ambient temperature in which the lamp will be tested, with a regulated voltage applied tothe lamp and, if appropriate, a reference set of control gear. If any of the aspects of the proposeddesign are unusual, e.g. high ambient temperature, vibration, switching cycle, operating attitudeetc., the manufacturer should be made aware of the conditions and will advise if they affect thelife and/or light output of the lamp.

Typical values of LLMF after a range of operating times, for some commonly used dischargelight sources are given in Table 21.2.

Table 21.2 Typical values of lamp lumen maintenance factor (LLMF) for some commonlyused discharge light sources after a range of hours of use

4

0.91

0.83

0.87

0.93

0.89

0.98

8

0.86

0.78

0.76

0.89

0.81

0.97

Light source

Triphosphor/multiphosphorfluorescent

Halophosphor fluorescent

Mercury


Improved colour high pressure sodium

Low pressure sodium

Hours of use (thousands)

21.7.2 Lamp survival factor (LSF)Lamp survival factor is defined as the proportion of lamps of a specific type that are expected tobe emitting light after a number of hours of operation. Lamp survival factor should only beused in the calculation of maintenance factor when group lamp replacement, without spotreplacement, is to be done.

As with lamp lumen maintenance factor it is essential to consult manufacturers’ data. Thesedata will be based on assumptions such as switching cycle, supply voltage and control gear.If the expected operating conditions depart from these assumptions, manufacturers should be informed and asked for advice on how the actual conditions might affect lamp survival. Typical values of LSF after a range of operating times, for some commonly used discharge light sources are given in Table 21.3.


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Table 21.3 Typical values of lamp survival factor (LSF) for some commonly used dischargelight sources after a range of hours of use

0.1

1

1

1

1

1

0.5

1

1

1

1

1

1.0

1

1

1

1

1

1.5

1

1

1

1

0.99

2

1

1

0.99

0.99

0.98

6

0.99

0.99

0.97

0.96

0.90

10

0.85

0.85

0.92

0.92

0.65

12

0.75

0.75

0.88

0.89

0.50

14

0.64

0.64

0.84

0.85

-

4

1

1

0.98

0.98

0.96

8

0.95

0.95

0.95

0.94

0.79

Light source

Triphosphor/multiphosphorfluorescent

Halophosphor fluorescent

Mercury


Improved colour high pressure sodium

Hours of use (thousands)

21.7.3 Luminaire maintenance factor (LMF)Dirt deposited on or in a luminaire will cause a reduction in light output from the luminaire.The rate at which dirt is deposited depends on the construction of the luminaire, the nature ofthe dirt and the extent to it is present in the atmosphere. The luminaire maintenance factor(LMF) is the ratio of the light output of a luminaire at a given time to the initial light output.Tables 21.4 to 21.6 give typical values of LMF for six different types of luminaires and sixdifferent luminaire cleaning intervals, for clean, normal and dirty environments respectively.Clean environments are found in such locations as clean rooms, computer centres, electronicassembly areas and hospitals. Normal environments are found in offices, shops, schools,laboratories, restaurants, warehouses and so on. Dirty environments are common in steelworks,chemical works, foundries, woodwork areas and similar locations.


Table 21.6 Typical luminaire maintenance factors (LMF) for a range of luminaires, and arange of cleaning intervals, in dirty environments

Table 21.5 Typical luminaire maintenance factors (LMF) for a range of luminaires, and arange of cleaning intervals, in normal environments

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0.5

0.95

0.95

0.93

0.92

0.96

0.92

1.0

0.93

0.90

0.89

0.88

0.94

0.86

1.5

0.91

0.87

0.84

0.85

0.92

0.81

2.0

0.89

0.84

0.80

0.83

0.91

0.77

2.5

0.87

0.82

0.77

0.81

0.90

0.73

3.0

0.85

0.79

0.74

0.79

0.90

0.70

Luminaire type

Bare lamp batten

Open top reflector(ventilated)

Closed top reflector(unventilated)

Enclosed (IP2X)

Dustproof (IP5X)

Indirect uplighter

Time between luminaire cleaning (years)

Table 21.4 Typical luminaire maintenance factors (LMF) for a range of luminaires, and arange of cleaning intervals, in clean environments

0.5

0.92

0.91

0.89

0.87

0.93

0.89

1.0

0.89

0.86

0.81

0.82

0.90

0.81

1.5

0.87

0.83

0.74

0.79

0.88

0.73

2.0

0.84

0.80

0.69

0.77

0.86

0.66

2.5

0.82

0.76

0.64

0.75

0.85

0.60

3.0

0.79

0.74

0.61

0.73

0.84

0.55

Luminaire type

Bare lamp batten



Enclosed (IP2X)

Dustproof (IP5X)

Indirect uplighter


0.5

0.88

0.88

0.83

0.83

0.91

0.85

1.0

0.83

0.83

0.72

0.77

0.86

0.74

1.5

0.80

0.79

0.64

0.73

0.83

0.65

2.0

0.78

0.75

0.59

0.71

0.81

0.57

2.5

0.75

0.71

0.54

0.68

0.80

0.51

3.0

0.73

0.68

0.52

0.65

0.79

0.45

Luminaire type

Bare lamp batten



Enclosed (IP2X)

Dustproof (IP5X)

Indirect uplighter



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21.7.4 Room surface maintenance factor (RSMF)Changes in room surface reflectance caused by dirt deposition will cause changes in theilluminance produced by the lighting installation. The magnitude of these changes is governedby the extent of dirt deposition and the importance of inter-reflection to the illuminanceproduced. Inter-reflection is closely related to the distribution of light from the luminaire andthe room index. For luminaires that have a strongly downward distribution, i.e. directluminaires, inter-reflection has little effect on the illuminance produced on the horizontalworking plane. Conversely, indirect lighting is completely dependent on inter-reflections. As forroom index, the smaller is the room index, the greater is the contribution of inter-reflected light.

Tables 21.7 to 21.9 show the typical changes in the illuminance from an installation that occurwith time due to dirt deposition on the room surfaces, for clean, normal and dirty conditions, insmall, medium or large rooms, lit by direct, direct/indirect and indirect luminaires. Cleanenvironments are found in such locations as clean rooms, computer centres, electronic assemblyareas and hospitals. Normal environments are found in offices, shops, schools, laboratories,restaurants, warehouses and so on. Dirty environments are common in steelworks, chemicalworks, foundries, woodwork areas and similar locations.

Table 21.7 Room surface maintenance factor (RSMF) for direct, direct/indirect and indirect luminaires in rooms of different room indices, for a range of cleaning intervals, in clean environments

0.5

0.97

0.94

0.90

0.98

0.95

0.92

1.0

0.97

0.90

0.85

0.98

0.92

0.88

1.5

0.96

0.89

0.83

0.97

0.90

0.86

2.0

0.95

0.87

0.81

0.96

0.89

0.84

2.5

0.94

0.85

0.77

0.96

0.87

0.81

3.0

0.94

0.84

0.75

0.96

0.86

0.78

Room index

0.7

0.7

0.7

2.5 to 5

2.5 to 5

2.5 to 5

Interval between cleaning (years)

Luminaire type

Direct

Direct/indirect

Indirect

Direct

Direct/indirect

Indirect

Table 21.8 Room surface maintenance factor (RSMF) for direct, direct/indirect and indirect luminaires in rooms of different room indices, for a range of cleaning intervals, in normal environments

0.5

0.96

0.88

0.84

0.97

0.90

0.87

1.0

0.94

0.86

0.78

0.96

0.88

0.82

1.5

0.94

0.83

0.75

0.96

0.86

0.79

2.0

0.93

0.82

0.73

0.95

0.85

0.77

2.5

0.92

0.80

0.70

0.95

0.84

0.74

3.0

0.92

0.79

0.68

0.95

0.82

0.72

Room index

0.7

0.7

0.7

2.5 to 5

2.5 to 5

2.5 to 5


Luminaire type

Direct

Direct/indirect

Indirect

Direct

Direct/indirect

Indirect


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Table 21.9 Room surface maintenance factor (RSMF) for direct, direct/indirect and indirect luminaires in rooms of different room indices, for a range of cleaning intervals, in dirty environments

0.5

0.95

0.84

0.80

0.96

0.86

0.83

1.0

0.93

0.82

0.73

0.95

0.85

0.77

1.5

0.92

0.80

0.69

0.95

0.83

0.74

2.0

0.90

0.78

0.66

0.94

0.81

0.70

2.5

0.89

0.75

0.63

0.94

0.79

0.67

3.0

0.88

0.74

0.59

0.94

0.78

0.64

Room index

0.7

0.7

0.7

2.5 to 5

2.5 to 5

2.5 to 5


Luminaire type

Direct

Direct/indirect

Indirect

Direct

Direct/indirect

Indirect

21.8 Determination of maintenance factor for exterior lighting

The maintenance factor (MF) for an outdoor lighting installation is a multiple of three factors:

MF = LLMF × LSF × LMF

where: LLMF is the lamp lumen maintenance factorLSF is the lamp survival factorLMF is the luminaire maintenance factor.

Typical values of LLMF are given in Table 21.2. Typical values of LSF after different hours ofoperation are given in Table 21.3. Typical values of luminaire maintenance factor (LMF) forluminaires with different levels of dust proofing installed in different levels of atmosphericpollution and with different luminaire cleaning intervals are given in Table 21.10. The level ofdust proofing is given by the IP class to which the luminaire belongs (see Table 4.10). Lowatmospheric pollution occurs in rural areas. Medium atmospheric pollution occurs in semi-urban, residential and light industrial areas. High atmospheric pollution occurs in large urbanareas and heavy industrial areas.

Table 21.10 Typical luminaire maintenance factor (LMF) for luminaires of different IP classes, in different levels of atmospheric pollution over a range of cleaning intervals

1.0

0.82

0.62

0.53

0.92

0.90

0.89

0.93

0.92

0.91

1.5

0.80

0.58

0.48

0.91

0.88

0.87

0.92

0.91

0.90

2.0

0.79

0.56

0.45

0.90

0.86

0.84

0.91

0.89

0.88

3.0

0.78

0.53

0.42

0.88

0.82

0.76

0.90

0.87

0.83

Luminaire IP class

IP2X

IP2X

IP2X

IP5X

IP5X

IP5X

IP6X

IP6X

IP6X

Luminaire cleaning interval (years)

Atmospheric pollution

Low

Medium

High

Low

Medium

High

Low

Medium

High


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21.9 Disposal of lighting equipment

Until recently, the disposal of lighting equipment was rarely discussed. However, theintroduction of the Waste Electrical and Electronic Equipment (WEEE) Regulations have made itnecessary for the designer to consider how lighting equipment is to be disposed of at the end oflife. The purpose of the WEEE regulations is to reduce the impact of electrical and electronicequipment on the environment but encouraging recycling and reducing the amount of suchwaste that goes to landfill. With the exception of lighting equipment in households and filamentlight sources anywhere, all lighting equipment, lamps, luminaires and control systems, is nowconsidered hazardous waste. Recently two organisations have been established in the UK, which can advise on the disposal of redundant lighting equipment. They are Recolight(www.recolight.co.uk) for lamp disposal and Lumicon (www.lumicon.co.uk) for luminairedisposal. Guidance on the implementation of the WEEE Regulations as they apply to lighting is available from the Lighting Industry Federation.


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Chapter 22: On the horizon

22.1 Changes and challenges

Lighting practice does not exist in a vacuum. Rather, lighting practice occurs within a businessand social environment and that environment is always changing. The resulting changes andchallenges can be gradual or sudden; technical, economic or political, but all are likely to resultin adjustments in lighting practice. This chapter is concerned with the sort of changes andchallenges that are already on the horizon and that are likely to impact lighting practice in theforeseeable future.

22.2 The changes and challenges facing lighting practice

22.2.1 CostsCosts have always been an important consideration for lighting applications, the balancebetween first and operating costs changing as the price of electricity has changed. The price ofelectricity varies with the source of fuel. In the UK, recent increases in demand for oil and gasand reductions in supply have resulted in dramatic increases in the price of electricity. Whateverthe cause, any increase in the cost of electricity implies a shift in emphasis to operating costsand enthusiasm for technologies that minimise electricity consumption and maximise energyefficiency, together with a closer examination of the basis of many lighting recommendations.

22.2.2 TechnologiesLight emitting diodes (LEDs)Lighting is unique amongst technologies in that the first electric light source invented, theincandescent lamp, is still the most widely used. This is in spite of the ingenuity of the lightingindustry, which has produced a dazzling array of new light sources with much greater luminousefficacies, longer lives and a wide range of colour properties. However, the reign of theincandescent lamp is under threat from influential forces and new technology. The influentialforces are those who see the elimination of the cheap but inefficient incandescent lamp asdesirable for environmental, political or commercial reasons. The new technology is the LED.LEDs have already displaced the incandescent lamp from many signs and signals, are starting toappear in near field lighting installations such as reading lamps, and are poised to make thebreakthrough into general illumination. When they do they will not only show improvementson existing criteria, such as luminous efficacy and lamp life, but also offer new possibilities,such as luminaires which allow changes in light level, light distribution and light spectrum tobe made quickly and easily.

Lighting controlsLighting control systems are becoming more sophisticated. This is now possible for a numberof reasons. First, enormous amounts of computer power are now available in very smallpackages. Second, developments in wireless communication have enhanced flexibility andremoved the need for expensive rewiring. Third, there are a number of widely recognisedcommunication protocols that enable equipment from different manufacturers to worktogether. As a result of these changes the integration of daylight and electric lighting is mucheasier, individual control of electric lighting is a real possibility, and the dimming of roadlighting at night as traffic flows diminish is being seriously considered (Walker, 2007).

22.2.3 New knowledgeThere are a number of areas in which research is revealing an understanding that has importantimplications for lighting practice.


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Light and healthFor most of the last century, light was considered solely in terms of its impact on our ability tosee. However, it has been known for some time that exposure to optical radiation can have bothpositive and negative impacts on human health, impacts that can become evident soon afterexposure or only after many years. Optical radiation covers the ultra-violet, visible and infraredregions of the electromagnetic spectrum (see Figure 1.1). An example of the impact of opticalradiation is the production of vitamin D following exposure of the skin. Vitamin D is essentialfor healthy bones and influential in many other aspects of health (Holick, 2005). Unfortunately,optical radiation incident on the skin and eye is also known to produce tissue damage, bothacute and chronic, through either thermal or photochemical routes. There exist occupationalsafety guidelines limiting the exposure to optical radiation (ACGIH, 2004) and methods forevaluating electric light sources for their potential to cause tissue damage (IESNA, 1996).

These effects are well known, so it is the more recent discovery of a new class of photoreceptorin the retina of the eye that has renewed interest in light and health (Brainard et al, 2001;Thapan et al, 2001). The output from these photoreceptors is linked to the suprachiasmaticnuclei in the brain. These nuclei are believed to form the master clock for the body’s circadiansystem. The relevance of this finding for lighting practice is evident from the fact that patternsof light exposure have been shown to alleviate problems associated with diminished operationof the circadian system. For example, people with Alzheimer’s disease show a fracturedsleep/wake cycle, often being active at night. It has been shown that exposure to bright lightduring the day and little light at night restores the sleep/wake cycle to a more stable state (vanSomeren et al., 1997). Similarly, some people suffer from timing problems with sleep, youngpeople having delayed sleep phase syndrome and elderly people having advanced sleep phasesyndrome. Exposure to bright light at the correct time has been shown to correct these timingproblems, the exposure being in the morning for the young and the evening for the elderly(Czeisler et al., 1988; Campbell et al., 1993).

There is also the presently unexplained phenomenon of the use of light treatment to overcomeseasonally affective disorder (SAD), a condition in which people feel depressed during a specificseason, usually winter, but not during the rest of the year. Exposure to bright light has beenshown to diminish this depression in a significant number of people. Guidance on its use hasbeen developed (Lam and Levitt, 1999).

But it is not all good news. Concern has also been raised about the impact of light exposure atnight on the development of breast cancer (Figueiro et al, 2006). A lot more needs to be knownabout how the circadian system and all the other bodily functions linked to it might beinfluenced by light exposure before advocating the widespread use of light exposure forpurposes other than vision (Boyce, 2006; Figueiro et al, 2006). Once that knowledge is gained,then lighting is likely to be designed not just for vision but for human health as well.

Individual controlLighting has usually been specified and designed on a one-size-fits-all basis. However, researchhas shown that when office workers are given individual control of their lighting, the preferredilluminances can vary widely but the bulk of the illuminances chosen are below the levelsrecommended (Boyce et al, 2006a). These findings have two implications. The first is that one-size-fits-all lighting cannot hope to satisfy everyone, a fact made evident by the finding that forthe most common form of office lighting in North America, only about 70% of occupantsfinding the lighting comfortable (Eklund and Boyce, 1996). The second is that the change inoffice work produced by the almost universal use of self-luminous displays represents anopportunity to re-examine lighting recommendations.


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nScotopically enhanced lighting Research has demonstrated that light sources that more effectively stimulate the rodphotoreceptors of the eye improve visual acuity (Berman et al, 2006). This improvement iscaused by the smaller pupil size produced and hence the improvement in retinal image quality.This finding suggests that light sources with a high scotopic/photopic ratio can be used at lowerilluminance than those with a lower scotopic/photopic ratio to achieve equal visualperformance. This is certainly true for tasks that are limited by visual acuity but not for taskslimited by other factors (Boyce et al, 2003b) or for applications where appearance is moreimportant than visual performance. Nonetheless, this research has demonstrated that lightspectrum has an impact on task performance beyond simply colour rendering.

Mesopic visionMuch exterior lighting provides conditions such that the visual system is in the mesopic stateyet the measurements used to describe photometric conditions are all based on the photopicresponse. As a result, light sources that are calculated to be equal may be very different inreality. This is of particular concern for road lighting where interest is focused on the possibilitythat metal halide light sources may provide equal visibility at lower illuminances than the highpressure sodium light sources widely used at present (Fotios and Cheal, 2007a and b).Unfortunately, there is no internationally agreed system of mesopic photometry. Previousattempts to identify a standard observer for mesopic vision were based on the perception ofbrightness (CIE, 1989) but recently, alternative approaches based on reaction times (Rea et al,2004) and performance measurements related to driving (Elohoma and Halonen, 2006) havebeen published. A comparison between these two systems suggests that there is little differencebetween them at the luminances typically produced by exterior lighting (Rea and Bullough,2007). The CIE is attempting to develop a system for dealing with mesopic vision based onthese findings. Once such a system has been developed, a major reassessment of exteriorlighting practice is to be expected.

Replacement of the CIE general colour rendering index (CRI)Although the CIE General CRI has been used to characterise light sources for many years itdoes have a number of limitations. First, just because two light sources have the same generalCRI, it does not mean that they render colours the same way. The general CRI is an averageand there are many combinations of special CRI values that give the same average. Second,different light sources are being compared with different reference light sources. This makesthe meaning of comparisons between different light sources uncertain, yet comparing lightsources is what the general CRI is most widely used to do. Third, there is considerableargument about the method used to correct for chromatic adaptation. What has made the searchfor a replacement urgent is the development of improved or new light sources with differentcolour properties but which the general CRI is unable to separate. It is likely that anyreplacement for the general CRI will involve abandoning the use of a single number to describea phenomenon as complex as colour perception and the acceptance of something moresophisticated such as colour vector maps (van Kemenade and van der Burgt, 1988) or the colourgamut (see Section 1.4.5).

Replacement of daylight factorDaylight factor has been used to quantify the proportion of daylight available in an interior formany years. Unfortunately, daylight factor suffers from a serious limitation, namely that itassumes a uniform overcast sky. This is a problem in that real skies vary greatly from day to dayand from climate to climate. Thus, a realistic evaluation of the energy impact of any proposeddaylighting scheme demands that account be taken of the typical climate in which the buildingis situated as well as the orientation of the building.


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Alternative climate-based metrics, such as useful daylight illuminance, are being developed(Madaljevic, 2006). Such metrics would make the adoption of daylight as the primary lightsource in buildings easier to achieve.

Lighting the spaceCurrent lighting practice is divided into two parts. Where the appearance of the space isimportant to the impression given, e.g. for hotel foyers, the lighting designer is allowed freereign to use the lighting of the space to deliver the required ‘message’. In applications wherefunction is the main consideration, attention is focused on visual performance of tasks with theresult that the appearance of the space is often ignored. This dichotomy has triggered twodifferent streams of research. One is the search for the cues that people use in generating theirimpression of a space (Loe et al, 1994, 2000). By identifying the parts of the space that areimportant for perception and the aspects of light distribution and colour appearance thatinfluence perception, it is hoped to improve the quality of lighting design. The other is anattempt to demonstrate the value of lighting the space by measuring individual taskperformance under different types of interior lighting. This has been largely unsuccessful(Boyce et al 2006b). While it has been shown that people can identify better quality lighting andprefer it, there is no effect of lighting quality on task performance other than where there aredifferences in task visibility. This failure to find an effect of lighting quality beyond visibility ismost likely to be because the simulated work studies used measure what we can do, not whatwe might choose to do. To measure what people choose to do, studies have to be conducted inthe field where real people do real work. Until such studies are done and the possibility thatlighting the space may have an effect at an organisational level is investigated, the importance oflighting the space on task performance is a matter of belief and exhortation rather than proof.

22.2.4 External influencesLighting practice is under pressure from a number of external interests. The fact that lighting isa major consumer of electricity together with the relatively short time scales within whichlighting practice can be changed has attracted the attention of those concerned with energyconservation, global warming and sustainability. The aim of these interests is to reduce theamount of electricity used for lighting. One way to achieve this is to make daylight the primarylight source in buildings with electric lighting being used as a supplement when necessary.Another is to ban the sale of inefficient light sources and luminaires. Legislative, regulatory andpromotional activities in these areas are to be expected.

Another interest group influencing lighting practice is one concerned with light pollution for itseffects on the night sky and the surrounding flora and fauna. Light pollution can be consideredat two levels, the local, where it tends to be related to light trespass, and the regional, whereattention is given to sky glow. This group wishes to change lighting practice to reduce theamount and distribution of light used at night. There are a number of approaches beingdeveloped to reduce light pollution, varying from the simple advice to use full cutoff luminairesto the more sophisticated design tool that seeks to limit the amount of light leaving theboundary of the site (Brons et al, 2008). It is likely that concerns about light pollution will carrygreater weight in the design of exterior lighting in the future.

22.3 The evolution of lighting practice

Given that lighting practice faces a number of changes and challenges and is likely to beinfluenced by the interests of a number of groups whose concerns are more with theconsequences of lighting than with lighting itself, what can be done to guide how lightingpractice evolves?


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nThis question can be addressed through two other questions, what is it that motivates people towant some form of lighting and how should lighting practitioners react to external interests?

The basic framework for understanding what motivates people is given by Maslow’s hierarchyof needs (Maslow and Lowery, 1998). Graphically, this consists of a triangle formed of eightlevels (Figure 22.1). The lower four are called deficiencies. They represent needs that must bemet. The lowest need is simply the physiological need for food, water, sleep, warmth etc. Thesecond is the need for safety. The third is the need to belong, to be accepted as a member ofsome group. The fourth is the need for esteem from others.

The fifth to eight levels are called the growth levels and represent needs that are optional. They are, respectively, the need to know and understand, aesthetic needs, self-actualisationwhich means finding fulfillment, and transcendence, where the individual connects tosomething beyond the ego.

Figure 22.1 Maslow’s hierachy of needs

Within this structure, the lower needs must be met before moving to a higher level. Everyonestarts from the bottom and works their way up. Fewer and fewer reach each level. Anyone whoachieves transcendence is a saint. The question now is what has lighting got to contribute tothese needs? The answer is that lighting at its most basic contributes to the physiological needto see and to the need for safety. Lighting also has a role to play in the need to belong, becauselighting as an element of fashion can be used to define groups. It might also be argued thatlighting has a role in satisfying aesthetic needs, but the number of people who have achievedthis elevated level is small.

Trans-cendence

Self-actualisation

Aesthetic needs

Need to know and understand

Esteem needs

Belongingness and love needs

Safety needs

Physiological needs


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Overall, this is not a very encouraging picture. The contribution to the first and second levelsshould ensure that there will always be mass support for simple forms of lighting but the failureto be an essential component in the next levels suggests that attempts to develop mass aestheticappreciation of lighting will meet with limited success. The one ray of hope in all this is agrowth in our understanding of how exposure to light influences human health. The concernwith health operates at the first or second level and so could generate mass support fordevelopments in lighting practice.

The other possibility for mass support is to form an alliance with the groups who are concernedwith the consequences of lighting rather than lighting itself. This increases the number ofpeople for whom lighting operates at the third level. In a sense, lighting practitioners should beflattered by the attentions of these other groups. It means that like war and generals, lightinghas become too important to be left to lighting practitioners alone. Further, using emergingtechnologies and knowledge to meet the desires of groups concerned with sustainability andlight pollution represents an opportunity for lighting practitioners to demonstrate added value.Of course, such a course of action will require compromises from all parties but surely it isbetter to use our wits to work together rather than to defend the indefensible.

So, how will lighting evolve? There will always be a niche market for sophisticated lighting, butfor the bulk of lighting practice, the answer is one of two directions. In one direction theprospect is of lighting as a commodity driven solely by price with a limited range of standardequipment and designs. In the other the prospect is of a more sophisticated approach in whichnew technology, new understanding and new objectives combine to produce lighting bettersuited to the needs and concerns of mankind in the 21st century. Which of these directionslighting moves in will depend on the willingness of lighting practitioners to take advantage ofnew knowledge and technology and to cooperate with rather than confront apparentlyconflicting interests.


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Chapter 23: Bibliography

23.1 Standards

British Standards Institution BS 667: 2005: Illuminance meters. Requirements and test methods,London: BSI.

British Standards Institution BS 5266-1: 2005: Emergency lighting. Code of practice for the emergencylighting of premises, London: BSI.

British Standards Institution BS 5266-10: 2008: Guide to the design and provision of emergencylighting to reduce the risks from hazards identified by The Regulatory Reform (Fire Safety) Order 2005 riskassessment, London: BSI.

British Standards Institution BS 5394:1988, EN 55015: 1987: Specification for limits and methodsof measurement of radio interference characteristics of fluorescent lamps and luminaires, London: BSI.

British Standards Institution BS 5489-1: 2003+A2: 2008: Code of practice for the design of roadlighting. Lighting of roads and public amenity areas, London: BSI.

British Standards Institution BS 5489-2: 2003+A1: 2008: Code of practice for the design of roadlighting. Lighting of tunnels, London: BSI.

British Standards Institution BS 5499: Safety signs, including fire safety signs, London: BSI.

British Standards Institution BS 6387: 1994: Specification for performance requirements for cablesrequired to maintain circuit integrity under fire condition, London: BSI.

British Standards Institution BS 7846: 2000: Electric cables. 600/1000 V armoured fire-resistantcables having thermosetting insulation and low emission of smoke and corrosive gases when affected by fire,London: BSI.

British Standards Institution BS 7920: 2005: Luminance meters. Requirements and test methods,London: BSI.

British Standards Institution BS 8206-2: 2008: Lighting for buildings: Code of practice for daylighting, London: BSI.

British Standards Institution BS EN 12193: 2007: Light and lighting. Sports lighting,London; BSI.

British Standards Institution BS EN 12464-1: 2002: Light and lighting. Lighting of work places.Indoor work place, London; BSI.

British Standards Institution BS EN 13201-2: 2003: Road lighting. Performance requirements,London: BSI.

British Standards Institution BS ISO 15469: 2004: Spatial distribution of daylight. CIE standardgeneral sky , London; BSI.


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British Standards Institution BS EN 50171: 2001: Central power supply systems, London: BSI.

British Standards Institution BS EN 50172:2004, BS 5266-8: 2004: Emergency escape lightingsystem, London: BSI.

British Standards Institution BS EN 55016: Specification for radio disturbance and intensitymeasuring apparatus and method, London: BSI.

British Standards Institution BS EN 60061: Specification for lamp caps and holders together withgauges for the control of interchangeability and safety, London: BSI.

British Standards Institution BS EN 60064: 1995+A4: 2007: Tungsten filament lamps for domesticand similar general lighting purposes. Performance requirements, London: BSI.

British Standards Institution BS EN 60081: 1998, IEC 60081: 1997: Double-capped fluorescentlamps. Performance specifications, London: BSI.

British Standards Institution BS EN 60192: 2001, IEC 60192: 2001: Low pressure sodiumvapour lamps. Performance specifications, London: BSI.

British Standards Institution BS EN 60238: 2004: Edison screw lampholders, London: BSI.

British Standards Institution BS EN 60357: 2003: Tungsten halogen lamps (non-vehicle).Performance specification, London: BSI.

British Standards Institution BS EN 60400:2000, IEC 60400: 1999: Lampholders for tubularfluorescent lamps and starterholders, London: BSI.

British Standards Institution BS EN 60432: Incandescent lamps. Safety specifications,London: BSI.

British Standards Institution BS EN 60570: 2003: Electrical supply track systems for luminaires,London: BSI.

British Standards Institution BS EN 60598: Luminaires, London: BSI

British Standards Institution BS EN 60601: Medical electric equipment: general requirements forhuman safety and essential performance, London: BSI.

British Standards Institution BS EN 60601-2-41: Particular requirements for the safety of surgicalluminaires and luminaires for diagnosis, London: BSI.

British Standards Institution BS EN 60702: Mineral insulated cables and their terminations with arated voltage not exceeding 750 V, London: BSI.

British Standards Institution BS EN 60838: Miscellaneous lampholders, London: BSI.

British Standards Institution BS EN 60896: Stationary lead acid batteries, London: BSI.

British Standards Institution BS EN 60901:1996+A4: 2008: Single-capped fluorescent lamps.Performance specifications, London: BSI.


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yBritish Standards Institution BS EN 60920: 1991: Ballasts for tubular fluorescent lamps. Generaland safety requirements, London: BSI.

British Standards Institution BS EN 60921: Ballasts for tubular fluorescent lamps. Performancerequirements, London: BSI.

British Standards Institution BS EN 60923: 2005: Auxiliaries for lamps. Ballasts for dischargelamps (excluding tubular fluorescent lamps). Performance requirements, London: BSI.

British Standards Institution BS EN 60924: 1991: Specification for general and safety requirementsfor d.c. supplied electronic ballasts for tubular fluorescent lamps, London: BSI.

British Standards Institution BS EN 60925: 1991: Specification for performance requirements ford.c. supplied electronic ballasts for tubular fluorescent lamps, London: BSI.

British Standards Institution BS EN 60927: 2007: Auxiliaries for lamps. Starting devices (otherthan glow starters). Performance requirements, London: BSI.

British Standards Institution BS EN 60920: 1991: Ballasts for tubular fluorescent lamps. Generaland safety requirements, London: BSI.

British Standards Institution BS EN 60969: 1993: Self-ballasted lamps for general lightingservices. Performance requirements, London: BSI.

British Standards Institution BS EN 61000: Safety requirements for electronic equipment formeasurement, control and laboratory use, London: BSI.

British Standards Institution BS EN 61047: 2004: D.C. or A.C. supplied electronic step-downconvertors for filament lamps. Performance requirements, London: BSI.

British Standards Institution BS EN 61048: 2006: Auxiliaries for lamps. Capacitors for use intubular fluorescent and other discharge lamp circuits. General and safety requirements, London: BSI.

British Standards Institution BS EN 61049: 1993: Specification for capacitors for use in tubularfluorescent and other discharge lamp circuits. Performance requirement, London: BSI.

British Standards Institution BS EN 61056: Portable lead-acid cells and batteries (valve regulatedtype), London: BSI.

British Standards Institution BS EN 61184:1997, IEC 61184: 1997: Bayonet lampholders,London: BSI.

British Standards Institution BS EN 61195:2000, IEC 61195: 1999: Double-capped fluorescentlamps. Safety specifications, London: BSI.

British Standards Institution BS EN 61199:2000, IEC 61199: 1999: Single-capped fluorescentlamps. Safety specifications, London: BSI.

Industry Committee for Emergency Lighting (ICEL) ICEL: 1004: 2003: Requirements forthe re-engineering of luminaires for emergency lighting use, London: ICEL.


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International Standards Organisation BS EN ISO 11197: 2004: Medical supply units,Geneva: ISO

23.2 Guidance

American Conference of Governmental Industrial Hygienists (ACGIH), (2004) TLVs and BEIsThreshold limit values for chemical substances and physical agents, biological exposure indices, Cincinnati,OH: ACGIH.

Chartered Institution of Building Services Engineers CIBSE Lighting Guide 6: The outdoorenvironment, London: CIBSE.

Chartered Institution of Building Services Engineers CIBSE Factfile 2: Car park lighting —dilemma solved, London: CIBSE.

Chartered Institution of Building Services Engineers CIBSE Technical Memorandum 35:Environmental performance toolkit for glazed facades, London: CIBSE.

Commission Internationale de l’Eclairage CIE Publication 15:2004: Colorimetry, Vienna: CIE.

Commission Internationale de l’Eclairage CIE Publication 107: 1994 : Review of the officialrecommendations of the CIE for the colors of signal lights, Vienna: CIE.

Commission Internationale de l’Eclairage CIE Publication 112: 1994: Glare evaluation systems foruse with outdoor sports and area lighting, Vienna: CIE.

Commission Internationale de l’Eclairage CIE Publication 150: 2003: Guide on the limitation ofthe effects of obtrusive light from outdoor lighting installations, Vienna: CIE.

Commission Internationale de l’Eclairage CIE Publication 154:2003: Maintenance of outdoorlighting systems, Vienna: CIE.

Commission Internationale de l’Eclairage CIE S 015/E: 2005: Lighting of outdoor workplaces,Vienna: CIE.

Commission Internationale de l’Eclairage CIE Publication 169: 2005: Practical design guidelines forthe lighting of sports events for colour television and filming, Vienna: CIE.

Commission Internationale de l’Eclairage CIE Publication 97: 2005: Guide on the maintenance ofindoor electric lighting systems, Vienna: CIE.

Department for Education and Science Building Bulletin 90, BB90, Lighting design for schools,London: DfES (now the Department for Children, Schools and Families).

Department for Education and Science Building Bulletin 87, BB87, Guidelines for environmentaldesign in schools, London: DfES (now the Department for Children, Schools and Families).

Department for Education and Science Building Bulletin 77, BB77, Designing for pupils withspecial educational needs and disabilities in schools, London: DfES (now the Department forChildren, Schools and Families).


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yEBV Electronik, see www.ebv.com/thequintessence

Illuminating Engineering Society of North America, The IESNA Lighting Handbook, 9th Edition,New York: IESNA.

Illuminating Engineering Society of North America, ANSI/IESNA RP-27-96, Recommended practice for photobiological safety for lamps and lamp systems, New York: IESNA.

Institution of Lighting Engineers, Guidance notes for the reduction of obtrusive light, ILE, Rugby.

Institution of Lighting Engineers Technical Report 28: Measurement of road lighting performance on site, ILE, Rugby.

Joint statement (SLL, ECA, ILE, LIF) Means of assessing equal and approved, 2004.

Lighting Industry Federation, LED Guide – Light from the light emitting diode, 2005.

Lam, RW, and Levitt, AJ, (1999) Canadian consensus guidelines for the treatment of seasonal affective disorder, Vancouver, BC: Clinical and Academic Publishing.

NHS Estates Health Technical Memorandum 2022: Medical gas pipelines, London: NHS.

Philips Lumileds Lighting Company, see www.philipslumileds.com

Society of Light and Lighting SLL Code for lighting, London: CIBSE.

Society of Light and Lighting SLL Lighting Guide 1: Industrial lighting, London: CIBSE.

Society of Light and Lighting SLL Lighting Guide 2: Hospital & health care buildings,London: CIBSE.

Society of Light and Lighting SLL Lighting Guide 4: Sports lighting, London: CIBSE.

Society of Light and Lighting SLL Lighting Guide 5: Lecture, teaching and conference rooms, London:CIBSE.

Society of Light and Lighting SLL Lighting Guide 7: Office lighting, London: CIBSE.

Society of Light and Lighting SLL Lighting Guide 10: Daylighting and window design,London: CIBSE.

Society of Light and Lighting SLL Lighting Guide 11: Surface reflectance and colour, London: CIBSE.

Society of Light and Lighting SLL Lighting Guide 12: Emergency lighting design guide,London: CIBSE.

Society of Light and Lighting SLL Factfile 7: Environmental considerations for exterior lighting,London: CIBSE.

Society of Light and Lighting SLL Factfile 9: Lighting and the 2006 Building regulations,London: CIBSE.


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Society of Light and Lighting SLL Factfile 10: Providing visibility for an ageing workforce,London: CIBSE.

23.3 References

Berman, S.M., (1992) Energy efficiency consequences of scotopic sensitivity, Journal of the IlluminatingEngineering Society, 21, 3–14.

Berman, S.M., Navvab, M., Martin, M.J., Sheedy, J. and Tithof, W., (2006) A comparison oftraditional and high colour temperature lighting on the near acuity of elementary school children, LightingResearch and Technology, 38, 41–52.

Blackwell, H.R., (1959) Development and use of a quantitative method for specification of interiorillumination levels on the basis of performance data, Illuminating Engineering, 54, 317–353.

Boff, K.R., and Lincoln, J.E., (1988) Engineering data compendium: Human perception and performance, Wright-Patterson AFB, OH: Harry G. Armstrong Aerospace Medical Research Laboratory.

Boyce, P.R., (1979) The effect of fence luminance on the detection of potential intruders, Lighting Research and Technology, 11, 78–84.

Boyce, P.R., (2003) Human Factors in Lighting, London: Taylor and Francis.

Boyce, P.R., (2006) Lemmings, light and health, Light and Engineering, 14, 24–31.

Boyce, P., Eklund, N., Mangum, S., Saalfield, C., and Tang, L., (1995) Minimum acceptabletransmittance of glazing, Lighting Research and Technology, 27, 145–152.

Boyce, P.R., Eklund, N.H., Hamilton, B.J., and Bruno, L.D., (2000) Perceptions of safety at night indifferent lighting conditions, Lighting Research and Technology, 32, 79–92.

Boyce, P.R., Hunter, C.M., and Howlett, O., (2003a) The benefits of daylight through windows,Troy, NY: Lighting Research centre.

Boyce, P.R., Akashi, Y., Hunter, C.M. and Bullough, J.D., (2003b) The impact of spectral powerdistribution on the performance of an achromatic visual task, Lighting Research and Technology, 35, 141–161.

Boyce, P.R., Veitch, J.A., Newsham, G.R., Jones, C.C, Heerwagen, J., Myer, M. and Hunter,C.M., (2006a) Switching and dimming behaviour in offices, Lighting Research and Technology, 38,358–378.

Boyce, P.R., Veitch, J.A,, Newsham, G.R., Jones, C.C., Heerwagen, J., Myer, M. and Hunter,C.M., (2006b) Lighting quality and office work: Two field simulation experiments, Lighting Research and Technology, 38, 191–223.

Brainard, G.C., Hanifin, J.P., Greeson, J.M., Byrne, B., Glickman, G., Gerner, E. and Rollag,M.D., (2001) Action spectrum for melatonin regulation in humans: Evidence for a novel circadianphotoreceptor. Journal of Neuroscience 21, 6405–6412.


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yBrons, J.A., Bullough, J.D. and Rea, M.S., (2008) Outdoor site-lighting performance: A comprehensiveand quantitative framework for assessing light pollution, Lighting Research and Technology, 40, 201–224.

Campbell, S.S., Dawson, D. and Anderson, M.W., (1993) Alleviation of sleep maintenance insomniawith timed exposure to bright light, J. Am. Geriartr. Soc., 41,829–836.

Commission Internationale de l’Eclairage (CIE) (1989) CIE Publication 81: Mesopic photometry:History, special problems and practical solutions, Vienna: CIE.

Crisp, V.H.C. and Henderson, G., (1982) The energy management of artificial lighting, LightingResearch and Technology 14, 193–206.

Cuttle, C., (1979) Subjective assessments of the appearance of special performance glazing in offices,Lighting Research and Technology, 11, 140–149.

Cuttle, C, (2003) Lighting by design, London: Architectural Press.

Cuttle, C. (2007) Light for Art’s Sake: Lighting for artworks and museum displays, London:Butterworth-Heinemann.

Czeisler, C.A., Kronauer, R.E., Johnson, M.P., Allen, J.S. and Dumont, M., (1988) Action of lighton the human circadian pacemaker: Treatment of patients with circadian rhythm sleep disorders, in J.Horn(ed) Proc. Conf. Sleep '88. Stuttgart, Germany: Verlag.

Dalke, H., Littlefair, P. and Loe, D, (2003) Lighting and colour design for hospital environments,Watford: Building Research Establishment.

Dubois, M-C, (2003) Shading devices and daylight quality: An evaluation based on simple performanceindicators, Lighting Research and Technology, 35, 61–76.

Eklund, N.H. and Boyce, P.R., (1996) The development of a reliable, valid, and simple office lightingsurvey, Journal of the Illuminating Engineering Society, 25, 25–40.

Elohoma, M and Halonen, L., (2006) New model for mesopic photometry and its application to roadwaylighting, Leukos, 2, 263–293.

Figueiro, M.G., Rea, M.S. and Bullough, J.D., (2006) Does architectural lighting contribute to breastcancer, Journal of Carcinogenesis, 5. 20.

Fotios, S.A. and Cheal, C., (2007a) Lighting for subsidiary streets – lamps of different SPD, Part 1 –Visual performance, Lighting Research and Technology, 39, 215–232.

Fotios, S.A. and Cheal, C., (2007b) Lighting for subsidiary streets – lamps of different SPD, Part 1 –Brightness, lighting research and technology, 39, 233–249.

Goodman , C. Housing for people with sight loss: A Thomas Pocklington Trust design guide EP84,Bracknell: IHS BRE Press, 2008.

Hawkes, R.J., Loe, D.L. and Rowlands, E., (1979) A note towards the understanding of lighting quality,Journal of the Illuminating Engineering Society, 8, 111–120.


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He, Y., Rea, M.S., Bierman, A. and Bullough, J., (1997) Evaluating light source efficacy under mesopicconditions using reaction times, Journal of the Illuminating Engineering Society, 26, 125–138.Hecht, S., and Smith, E.L., (1936) Intermittent stimulation by light, VI Area and the relation betweencritical frequency and seeing, Journal of General Physiology, 19, 979–989.

Holick, M.F., (2005) Historical and new perspectives on the biologic effects of sunlight and vitamin D on health, Proceedings Lux Europa, Berlin, pp 20–24.

Hunt, D.R.G., (1979) Improved daylight data for predicting energy savings from photoelectric controls,Lighting Research and Technology, 11, 9–23.

Kaiser, P.K., and Boynton, R.M., (1996) Human color vision, Washington DC, Optical Society of America.

Keighly, E.C., (1973a) Visual requirements and reduced fenestration in offices - a study of multiple aperturesand window area, Building Science, 8, 32.

Keighly, E.C., (1973b) Visual requirements and reduced fenestration in office buildings - a study of windowshape, Building Science, 8, 311.

Leslie R.P. and Rodgers, P.A., (1996) The outdoor lighting pattern book, New York: McGraw-Hill.

Lighting Research Centre, (1998) Delta Portfolio: Mary McLeod Bethune Elementary School,Troy, NY: LRC.

Lighting Research Centre, (2001a) Delta Portfolio: Hudson Valley Community College, Troy, NY: LRC.

Lighting Research Centre, (2001b) Delta Portfolio: Ballston Spa High School, Troy, NY: LRC

Lighting Research Centre, (2001c) Delta Snapshot: Monhonasen High School MultimediaAuditorium, Troy, NY: LRC.

Lighting Research Centre, (2001d) Lighting the way: The key to independence, Troy, NY: LRC.

Littlefair, P.J., (1990) Innovative daylighting: Review of systems and evaluation methods, LightingResearch and Technology, 22, 1–17.

Littlefair, P.J., (1991) BR209 Site layout planning for daylight and sunlight: A guide to good practice,Building Research Establishment, Construction Research Communications, London: BRE.

Littlefair, P.J. (1995) BR303 Estimating daylight in buildings, Building Research Establishment,Construction Research Communications, London: BRE.

Littlefair, P.J., (1996) BR305 Designing with innovative daylight, Building Research Establishment,Construction Research Communications, London: BRE.

Littlefair, P. J., (1999) Solar shading of buildings, Garston, Watford: Building ResearchEstablishment.


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yLittlefair, P. J. and Aizlewoood, M.E., (1999) Calculating access to skylight, sunlight and solar radiationon obstructed sites in Europe, Garston, Watford: Building Research Establishment.

Littlefair, P.J., Aizlewood, M.E., and Birtles, A.B., (1994) The performance of innovative daylightingsystems, Renewable Energy, 5, 920–934.

Loe, D.L., (2003) Quantifying lighting energy efficiency: a discussion document, Lighting Research & Technology 35, 319–329.

Loe, D.L. and Mansfield, K.P. (1998) Daylighting Design in Architecture. Making the Most of aNatural Resource, Garston, Watford: Building Research Establishment.

Loe, D.L, Rowlands, E. and Watson, N.F. (1982) Preferred lighting conditions for the display of oil andwatercolour paintings, Lighting Research and Technology, 14, 173–192.

Loe, D.L., Mansfield, K.P. and Rowlands, E., (1994) Appearance of a lit environment and its relevancein lighting design: Experimental study, Lighting Research & Technology 26, 119–133.

Loe, D.L., Mansfield, K.P. and Rowlands, E., (2000) A step in quantifying the appearance of a litscene, Lighting Research & Technology 32, 213–222.

Lynes, J.A. and Cuttle, C, (1988) Bracelet for total solar shading, Lighting Research and Technology,20, 105–113.

Lyons, S.L. (1980) Exterior lighting for industry and security, London: Applied Science Publishers.

MacAdam, D.L., (1942) Visual sensitivity to color differences in daylight, Journal of the OpticalSociety of America, 32, 247–274.

Mangum, S.R., (1998) Effective constrained illumination of three-dimensional, light-sensitive objects,Journal of the Illuminating Engineering Society, 27, 115–131.

Mardaljevic, J., (2006) Examples of climate-based daylight modelling, Proceedings of the CIBSENational Conference, London: CIBSE.

Maslow A and Lowery AJ, Toward a psychology of being, Wiley and Sons, New York, 1998.

Megaw, E.D., and Richardson, J., (1979) Eye movements and industrial inspection, AppliedErgonomics, 10, 145–154.

Phillips, D (1997) Lighting historic buildings, New York: McGraw Hill.

Phillips, D.R.H., (2004) Daylighting, natural light in architecture, London: Elsevier.

Rea, M.S., (1986) Toward a model of visual performance: Foundations and data, Journal of theIlluminating Engineering Society, 15, 41–58.

Rea, M.S. and Bullough, J.D., (2007) Move to a unified system of photometry, Lighting Research andTechnology, 39, 393–408.


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Rea, M.S. and Ouellette, M.J., (1991) Relative visual performance: A basis for application, LightingResearch and Technology, 23, 135–144.

Rea, M.S., Bullough, J.D., Freyssinier-Nova, J-P. and Bierman, A., (2004) A proposed unifiedsystem of photometry, Lighting Research and Technology, 36, 85–11.

Saalfield, C. (1995) The effect of lamp spectra and illuminance on color identification, Master of Sciencein Lighting thesis, Troy, NY: Lighting Research centre.

Sekular, R., and Blake, R., (1994) Perception, New York: McGraw-Hill.

Shlaer, S., (1937) The relation between visual acuity and illumination, Journal of General Physiology,21, 165–168.

Steward, J.M and Cole, B.L. (1989) What do colour defectives say about everyday tasks, Optometryand Vision Science, 66, 288–295.

Thapan, K., Arendt, J, and Skene, D.J, (2001) An action spectrum for melatonin suppression: Evidencefor a novel non-rod, non-cone photoreceptor system in humans, Journal of Physiology, 535, 261–267.

Thomas Pocklington Trust, (2008) Housing for people with sight loss: A design guide, London:Thomas Pocklington Trust.

Tielsch, J.M., (2000) The epidemiology of vision impairment, in B.Silverstone, M.A. Lang, B.P.Rosenthal, and E.E. Faye (eds) The Lighthouse handbook on vision impairment and visionrehabilitation, New York: Oxford University Press.

Tielsch, J.M., Sommer, A., Witt, K., Katz, J., and Royall, R.M., (1990) Blindness and visualimpairment in an American urban population, Archives of Ophthalmology, 108, 286-290.

Turner, J. (1998) Designing with light: Retail spaces; Lighting installations for shops, malls and markets,Hove, UK: Rotovision.

Van Bommel W.J.M. and Van Dyk J.P.M., (1984) Security lighting for domestic exteriors. Proceedingsof the IESNA Annual Conference, St. Louis.

Van Kemenade, J.T.C., and van der Burgt, P.J.M., (1988) Light sources and colour rendering:Additional information for the Ra Index, Proceedings of the CIBSE National Lighting Conference,Cambridge, London: CIBSE.

Van Someren, E.J.W., Kessler, A., Mirmiran, M., and Swaab, D.F., (1997) Indirect bright lightimproves circadian rest-activity rhythm disturbances in demented patients, Biol. Psychiatry, 41, 955–963.

Walker, T., (2007) Remote monitoring systems assessed, Lighting Journal, 72, 49–53.

Weston, H.C., (1945) The relation between illumination and visual efficiency: the effect of brightnesscontrast, Industrial Health Research Board, Report No. 87, London: His Majesty’s Stationery Office.


303

Ind

ex

Indexabsorption filters 91accent lighting 96, 193, 194accommodation, visual 26acoustic characteristics 93–94adaptation, visual 24–25, 29, 121adaptation glare 37air handling luminaires 91–92aluminium 85, 89, 279amalgams 62ambient temperature 79aperture mode 43arc tubes 70, 72architectural integration 120, 126area lighting

emergency lighting 142–143exterior workplaces 241–243security lighting 248, 249–250see also floodlighting

art galleries 198–202arts studios 187, 189assembly halls 187, 190atria 136autoleak transformer 111–112automatic controls 127–128, 158awnings 139

baffles 89–90ballasts 103, 104, 109–112

see also electronic control gearbattery powered systems 145, 153beam spread 105bedrooms 216, 218borrowed light 137brightness perception 42, 133British Standards (BS)

daylight requirements 133emergency lighting 140–141, 142luminaires 102–104road lighting luminaires 106

building facades 248, 250building management systems 147Building Regulations 118, 140building services, integration with 126bulb forms and materials

fluorescent lamps 61, 63high pressure mercury lamps 65–66high pressure sodium lamps 73incandescent lamps 58low pressure sodium lamps 70metal halide lamps 68tungsten halogen lamps 60

burning position 79

cabling see electrical circuitscandles 82canteens 163, 167, 181–182capacitors, standards 103, 104car parks 248, 253care homes 214–219cathodoluminescence 52CCT see correlated colour temperatures (CCT)CCTV surveillance 247CE mark 101, 102–104ceilings

height 158–159, 169luminous 172

ceramics 86certification 100–104, 155


304

Ind

ex

chemical industries 240–241chemiluminescence 52choke ballasts 110chromaticity, glazing 134chromaticity diagrams 8–10chromium, reflectance 89CIE

chromaticity diagrams 7–10classification, indoor luminaires 105Colour Matching Functions 7–8colour rendering index (CRI) 12–13, 289colour spaces 10–11daylight spectra 56publication list 296Spectral Luminous Efficiency Functions 2standard observers 1–2standard sky types 54–55

CIELAB 11CIELUV 11circulation areas

hospitals 206, 207industrial premises 181offices 164, 167quasi-domestic lighting 216

classification, luminaires 105–108, 148classrooms 187, 189cleaning 278–280clerestory windows 135colour appearance 63, 119, 167–168

see also correlated colour temperatures (CCT)colour filters 90–91colour gamut 13Colour Matching Functions 7–8colour order systems 14–15colour perception 42colour properties 78

fluorescent lamps 63high pressure mercury lamps 66high pressure sodium lamps 74lamp types 80–81light emitting diodes (LEDs) 76low pressure sodium lamps 70metal halide lamps 69

colour rendering index (CRI) 289colour rendering requirements 118, 119

educational premises 187exterior workplaces 239hospitals 203industrial lighting 175offices 167, 168retail premises 193–194security lighting 249

colour spaces 10–11, 14–15colour stability 68colour temperatures see correlated colour temperatures (CCT)colour thresholds 28, 31colour vision 23–24, 44–45colourimetry 7–15commissioning, emergency lighting 154–155communal dwellings 214–219compact fluorescent lamps 63–64computer rooms 187, 189computer screens see display screensconservation lighting 198–199Construction Products Directive 140contrast, luminance 26–27, 47control gear 109–114

requirement by lamp type 80–81standards 102


305

Ind

ex

control room lighting 178–180control systems 115–116, 125, 287

educational premises 188emergency lighting 147security lighting 256

correlated colour temperatures (CCT) 11–12daylight 56–57lamp types 80–81offices 167–168

costs 121, 287cove lighting 171CRI (colour rendering index) 289

DALI systems 116daylight 52–57

availability 55–56, 131–133colour temperatures 56–57luminance distribution 54–55, 131–132spectrum 56sun path and position 52–54

daylight factor 131–133, 289–290daylighting 129–139

advantages and disadvantages 129–130contribution to room brightness 133educational premises 186hospitals 203industrial lighting 174integration with 120, 126–128maintenance 137–139museums and galleries 198offices 158, 172quasi-domestic lighting 214remote distribution 136–137retail premises 192roles 124task illumination 133thermal problems 139types 133–135visual problems 137–139

diffuse reflectors 88, 89digital control systems 116dimming

dimmers 256lamp types 79, 80–81photo-electric controls 128

dining halls 216, 219direct lighting 94, 168–169direct/indirect lighting 95, 170discharge tubes

ballasts 109–112compact fluorescent 63–64diameters and lengths 62electronic control gear 112–114fluorescent lamps 61, 62, 63–64high pressure mercury lamps 65high pressure sodium lamps 72low pressure sodium lamps 70metal halide lamps 68

display lighting 195–196display screens 156–157, 165–166, 178–180

see also veiling reflectionsdisposal of lighting equipment 79, 94, 286DMX 512 116downlights 96drama studios 187, 190ducted exhaust systems 91–92dysprosium lamp 67


306

Ind

ex

earthing 85economic service life see service lifeeducational premises 185–190efficacy see luminous efficacyefficiency, luminaires 91electric discharges 49–50electrical circuits

emergency lighting 146–147luminaires 84–85

electrical connections, luminaires 84–85electrical insulation 84, 108electrical protection 107–108, 147, 215electrical safety

hospital lighting 204–205luminaire classification 107–108quasi-domestic lighting 215standards 100–103

electrical standards 100–103electrical testing, emergency lighting 154–155electrodes, lamp 61, 65, 72electroluminescence 51electroluminescent (EL) panels 76–77electro-magnetic compatibility (EMC) 146, 205Electro-Magnetic Compatibility (EMC) Directive 100, 101, 102electromagnetic control gear 109–112electronic control gear 112–114emergency lighting 140–155, 259–260

control rooms 179hospitals 204industrial premises 177quasi-domestic premises 215–216standards 103

emergency power sources 145–146EN (Euronorm) standards 100–104end caps 72ENEC mark 101, 103–104energy consumption 126–127

see also power demandenergy efficiency 120, 215, 290entrances

hospitals 206office buildings 164quasi-domestic buildings 217security lighting 248, 251

environmental conditions 106–107, 174environmental issues

disposal of lighting equipment 79, 94, 286integration with the surroundings 128light trespass 122–123, 238, 260skyglow 123–124, 238, 243, 290

environmental zones 122, 124escape route lighting 141–142Euronorm (EN) standards 100–104European Union Directives 100–102

emergency lighting 140lamp recycling 94

exterior lighting 98–100classification 105–108glare control 249illuminance measurement 274–275integration with the surroundings 128light trespass and skyglow 122maintenance factor 285public amenity areas 232–233workplace lighting 236–244

see also security lighting; sports lightingeye movements 17–18


307

Ind

ex

fibre-optic lighting 202filament design 58filling gas see gas fillingfilters 90–91fire protection 108, 215fire safety lighting see emergency lightingflammability, mounting surfaces 108flicker 41floodlighting 243

luminaires 99–100, 105fluorescence see luminescent light sourcesfluorescent lamps 60–64

baffles 89colour appearance and rendering 63compact 63–64diameters and lengths 62electromagnetic control gear 109–111gas filling 61–62induction lamps 74–75summary of characteristics 80

fuel industries 240–241

games rooms 216, 218gas filling

fluorescent lamps 61–62high pressure mercury lamps 65high pressure sodium lamps 73incandescent lamps 58–60low pressure sodium lamps 70metal halide lamps 66–67

gas lighting 83gatehouses 248, 251general colour rendering index (CRI) see colour rendering index (CRI)General Lighting Service (GLS) lamp 57–58generators 146glare 37–39glare control 118

daylighting 137–138educational premises 187exterior workplaces 239industrial lighting 176, 181office lighting 166–167road lighting 223security lighting 249

glassabsorption filters 91luminaires 85spectral transmittance 91, 134

glazing see windowsglossiness perception 43glow starters 110GLS (General Lighting Service) lamp 57–58

halls of residence 214–219halophosphates 61hazardous situations 144, 174, 177health issues 288

daylighting 130visual discomfort 37–44

high intensity discharge (HID) lampscontrol gear 111–114

high mast floodlighting 243high pressure mercury lamps 64–66, 80high pressure sodium lamps 70–74, 81, 112high risk areas see hazardous situationshospitals 203–213housing see multi-occupancy dwellings; private houseshue perception 43


308

Ind

ex

ignition see starters/ignitorsilluminance 4

daylighting 131distribution 119, 275–276

daylighting 138exterior lighting 98–100interior lighting 94–97measurement 272–275offices 164–165optical control 86–91

maintained illuminance 280measurement 155, 272–276

meters 271units 5–6

uniformity 37, 118, 276visual performance 33–34

illuminances, recommended 118educational premises 187emergency lighting 143–144exterior workplaces 238hospitals 206–213industrial lighting 177–182museums and galleries 199offices 162–166quasi-domestic lighting 216retail premises 192–193road lighting 220–225security lighting 247–248sports lighting 261–266

illuminant mode 43incandescence 48–49incandescent lamps 57–58, 80indirect lighting 158–159, 169–170

luminaires 95individual control 288indoor arenas 268indoor lighting see interior lightinginduction lamps 74–75industrial lighting 172inspection, emergency lighting 153–154installation, emergency lighting 153instrumentation 271–272insulation see electrical insulationintegrated lighting 243integration issues 125–128interference filters 91interior design 126interior lighting

architectural integration 120, 126classification 105illuminance measurement 272–274maintenance factor 280–285types 94–97visual function 118

International Protection (IP) system 106–107ionised gas discharge 49–50IT rooms 187, 189

kitchens 163, 216, 218

laboratory lighting 187, 189lamp lumen maintenance factor (LLMF) 281lamp replacement 278lamp size 79lamp survival factor (LSF) 78, 149, 281–282lampholders, standards 103lecture halls 187, 189LEDs (light emitting diodes) 75–76, 81, 114, 287


309

Ind

ex

legal requirements 118emergency lighting 140industrial lighting 173–174office lighting 156–157

libraries 163, 167, 187, 190life see service lifelight distribution see illuminance, distributionlight emitting diodes (LEDs) 75–76, 81, 114, 287light oscillation 177light output ratio (LOR) 91light pipes 136–137light pollution see light trespass; skyglowlight radiation 48–52

electric discharges 49–50luminescence 51–52spectral power distribution 48–49

light shelves 138light spectrum 1light trespass 122–123, 238, 260light-boxes 202lighting columns 98–99, 255–256

see also road lightinglighting controls see control systemslighting design 117–128, 288–290lightness perception 42, 43LLMF (lamp lumen maintenance factor) 281LMF (luminaire maintenance factor) 282–283loading bays 239–240localised lighting

exterior workplaces 244industrial lighting 183offices 170–171see also task lighting

LOR (light output ratio) 91louvres

baffles 90solar shading 138–139

low pressure sodium lamps 69–70, 81, 111–112low voltage light sources 114Low Voltage (LV) Directive 100, 101LSF (lamp survival factor) 78, 149, 281–282lumen maintenance 78, 281luminaire maintenance factor (LMF) 282–283luminaires 84–108

certification 100–104, 155classification 105–108, 148cleaning 278–280construction 86efficiency 91electrical connections 84–85emergency lighting 145, 147–149exterior lighting 98–100interior lighting 94–97maintenance 226materials 85–86optical control 86–91self-contained 145, 147standards 100–106substitutions 128thermal characteristics 91–93, 108

luminance 4daylighting 131–132measurement 276

meters 271–272units 5–6

luminance coefficient 4, 226–228luminance contrast 26–27, 47luminescent light sources 51–52, 149


310

Ind

ex

luminous ceilings 172luminous efficacy 78, 80–81luminous efficiency functions 2, 20luminous exitance 6luminous flux 3, 77

distribution, luminaire classification 105as a function of temperature, fluorescent lamps 62lamp types 80–81

luminous intensitydistribution, luminaire classification 105–106emergency lighting 143measurement 3

LV (Low Voltage) Directive 100

magnifiers 184maintained illuminance 280maintenance 278–286

daylighting 139emergency lighting 153–154lighting design 121, 280road lighting 226

maintenance factor (MF) 280–285manual switching 115, 126–127materials, luminaires 85–86measurement methods 3–6, 272–277measurement units 5–6meeting rooms 167, 187, 190mercury gas discharge 50mercury vapour lamps see fluorescent lamps; high pressure mercury lampsmesopic vision 25, 121, 289mess rooms 181–182metal halide lamps 66–69, 80, 112MF (maintenance factor) 280–285modes of appearance 42–44Modified Photopic Observer 2motion detectors see presence detectorsmounting surfaces, flammability 108multi-occupancy dwellings 254multi-phosphors 61, 63museums 198–202music rooms 187, 190

night vision 2noise rating (NR) 93–94

object modes 43occupant controls 126–127, 288office lighting 156–172oil lamps 82–83operating conditions

hazardous situations 144, 174, 177industrial lighting 174luminaire classification 106–107performance verification 270

operating theatres 212–213operational costs 121, 287optical control, luminaires 86–91output ranges, lamp types 80–81overhangs 138overheating 108, 215

painted surfaces 89, 161, 279parks see public areasPCA (polycrystalline alumina) 72pedestrian areas 224–225, 230–233

luminaires 98–99see also public areas

perception, visual 41–44


311

Ind

ex

performancestandards 104verification 270–277visual 32–34

perimeter fences 248, 250–251petrochemical industries 240–241phosphor coatings 61photochemical adaptation 25photo-electric controls 115, 127–128, 256photoluminescence see luminescent light sourcesphotometric testing 155photometry 3–6, 272–277photopic vision 2, 3, 14, 25, 121plant rooms 164, 167, 182plastics 85, 91, 279plenum exhaust systems 91–92‘ply-glass’ tube 70polycrystalline alumina (PCA) 72post top luminaires 98–99power demand 77, 120

see also energy consumptionpower factor 77–78power ranges, lamp types 80–81presence detectors 115, 256privacy problems, daylighting 139private houses, security lighting 253–254protection, luminaire classification 106–107public areas 248

amenity areas 232–233public parks 248, 253security lighting 248, 252–253see also pedestrian areas

radioluminescence 51railway sidings and yards 241–242reception areas 164, 206, 216recycling regulations 94reflectance 4–5

computer screens 156–157luminaire reflectors 89measurement 276–277

units 5–6road surfaces 226–228surface finishes 159–161

reflectors 86–88refractors 88relative visual performance (RVP) 34residential accommodation 214–219restaurants 163, 167Restriction of Hazardous Substances Directive (RoHS) 94restrike time 79retail lighting 191–197road lighting 220–235

luminaires 98, 106, 228–230road surfaces, reflection properties 226–228RoHS (Restriction of Hazardous Substances Directive) 94rooflights 135–136room surface maintenance factor (RSMF) 284–285rotating machinery 177RSMF (room surface maintenance factor) 284–285run-up 65, 78–79, 80–81RVP (relative visual performance) 34

safetyhospital lighting 204–205industrial lighting 177quasi-domestic lighting 215standards 100–103see also electrical safety; emergency lighting; fire protection


312

Ind

ex

safety signs 142, 149saturation perception 43scandium lamp 67schools see educational premisesscience laboratories 187, 189scotopic vision 2, 3, 14, 25scotopically enhanced lighting 289scotopic/photopic ratio 14secondary reflector luminaires 99security lighting 201, 216, 245–256selection process 124–125self-contained luminaires 145, 147seminar rooms 167, 187, 190service life 78, 149

lamp replacement 278lamp types 80–81

service stations 248, 253shading devices, glare reduction 138–139shadows 40–41shape perception 42shops see retail lightingshowcase lighting 202signage, escape routes 142Signs Directive 140size perception 42sky types, CIE standard 54–55skyglow 123–124, 238, 243, 290skylight 54–57skylights 135–136slave luminaires 147–148Society of Light and Lighting (SLL)

Lighting Guides 297sodium gas discharge 50sodium lamps see low pressure sodium lampssolar gain 139solar shading 135, 138–139

see also daylight; sun path and positionspatial thresholds 26–27, 28–30Spectral Luminous Efficiency Functions 2spectral power distribution 3, 7–8, 48–49

high pressure sodium lamps 71metal halide lamps 67scotopic/photopic ratio 14

spectral radiant exitance 48spectral sensitivity 1–2, 7–8, 14, 20spectral transmittance 91, 134specular reflectors 86–88, 89sports lighting 257–269spotlights 96, 105spread reflectors 88, 89stable running 65stadia see sports lightingStandard Photopic Observer 1–2Standard Scotopic Observer 2standard sky types 54–55standards

daylight requirements 133emergency lighting 140–141, 142luminaires 100–106references 293–296road lighting luminaires 106

standby lighting 144starters/ignitors

fluorescent lamps 110high intensity discharge (HID) lamps 112high pressure mercury lamps 65standards 103, 104see also electronic control gear

steel 85, 279


313

Ind

ex

storage areas 164, 180–181, 182street lighting, standards 103

see also pedestrian areas; road lightingstroboscopic effects 177, 184study bedrooms 216, 218substitutions 128sun path and position 52–54suprathreshold performance 32–34surface mode 43, 44surface reflectance see reflectancesurfaces see mounting surfacessurge-protection devices 147sustainability issues 120–121, 290

see also environmental issuesswimming pools 266, 268–269switching behaviour 126–127system choice 124–125

task lighting 170–171daylighting 133requirements 118task lights 97visual inspection 183–184

task performance 33television sports broadcasting 258–259temperature, running 79temporal thresholds 28, 30–31testing, emergency lighting 153–154thermal characteristics, luminaires 91–93thermal problems

overheating 108, 215solar gain 135, 139

thermoluminescence 52three colour metal halide lamp 67through wiring 85thulium lamp 67timers 115, 256tin halide lamp 67track systems, standards 103traffic route lighting 225–226transformers

low voltage light sources 114standards 103, 104

transparency perception 43tri-phosphors 61, 63tritium powered signs 149trunking systems 84–85tubes see discharge tubestungsten halogen lamps 59–60, 114tunnel lighting 233–235types of system

luminaires 94–100

Unified Glare Rating (UGR) 39uninterruptible power supplies (UPS) 145–146units of measurement 5–6urban centres 232–233

see also public areasutility rooms 218

veiling reflections 39–40daylighting 137museums and galleries 200see also display screens

vision, human 16–47visual accommodation 26visual acuity 27visual adaptation 24–25, 29, 121visual aids 184, 186


314

Ind

ex

visual amenity 119–120, 290visual anomolies 44–47visual attributes 42–43visual discomfort 37–44visual field 16–17visual function 118visual impairment 45–47visual inspection, lighting for 183–184visual perception 41–44visual performance 32–34visual problems 37–44

see also glare control; veiling reflectionsvisual search 34–36visual thresholds 26–32, 45–47volume mode 43, 44

wall washers 97, 195wallpacks 100warehouses 180–181Waste Electrical and Electronic Equipment Directive (WEEE) 94white high pressure sodium lamp 74windows 133–134

blinds 139, 161glare reduction 137maintenance issues 139

wiring see electrical circuitsWorkplace Directive 140workshops 164, 167, 175–176, 182workstation lighting 170–171

see also display screens


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The SLL Lighting Handbook

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