MECH3005 Building Servicesghttp://www.hku.hk/bse/mech3005/

Lighting System Design Lighting System Design Design Methods

Dr. Sam C M HuiDepartment of Mechanical EngineeringDepartment of Mechanical Engineering

The University of Hong KongE-mail: cmhui@hku hkE mail: cmhui@hku.hk

Sep 2010

Content

Basic PrinciplesBasic Principles

Design Process

Design Factors & Issues Design Factors & Issues

Lighting Calculations

Basic Principles

Three main functions of lighting:Three main functions of lighting: Ensure the safety of people Facilitate the performance of visual tasks Aid the creation of an appropriate visualAid the creation of an appropriate visual

environment (appearance & character)

Basic Principles

Two sources of light:Two sources of light: Natural sources of light (daylight)

People prefer daylight to windowless rooms Windows provide a view & connection to outdoor

Artificial or man-made (electric light)El i li h i d h d li h i h ld b Electric lighting and the daylighting should be complementary to ensurep y Efficient use of energy

i h li li h i High quality lighting

General lighting

[Source: CIBSE Lighting Code]

Localised lighting

[Source: CIBSE Lighting Code]

Local (task) lighting

[Source: CIBSE Lighting Code]

Set the goals

Specify criteria

S t tSystem type

Calculations/details

V ifi i

deta s

Verification

Lighting design and planning[Source: CIBSE Lighting Code]

Design Process

Basic approach to lighting designBasic approach to lighting design Determine lighting design criteria

Quantity of illumination (lighting level, lux) Quality of illumination (e.g. overall appearance, colour) Codes and regulations (e.g. building, electrical, energy)

Record architectural conditions & constraints e g Record architectural conditions & constraints, e.g. Window location & size, ceiling height, finish materials

Determine visual functions & tasks to be served Select lighting system to be usedSelect lighting system to be used

Design Process

Basic approach to lighting design (contd)Basic approach to lighting design (cont d) Select luminaire and lamp types

To produce the desired light & fit the clients needs Determine number & location of luminaires

Through calculations & assessmentPl it hi & th t l d i Place switching & other control devices

User convenience & energy management Aesthetic & other intangibles

Aesthetic & psychological factorsAesthetic & psychological factors

Design Process

Typical lighting controlsTypical lighting controls Switches Occupancy sensing Scheduling (timeclocks)Scheduling (timeclocks) Daylight dimming Tuning Preset dimming Preset dimming Building management

Design Factors & Issues

Important to consider:p Situation is it a working, viewing, circulation or

a living space?a living space? Function what will people do in the space? Quantity and Quality of Light what's needed to

perform the tasks? Architecture and Dcor consider the aesthetic of

the spacep Atmosphere what is the mood or ambience of

the space?the space?

Design Factors & Issues

Lighting quality and criteriag g q y Lighting level (lux or luminance e.g. road lighting)

L i di t ib ti Luminance distribution Better distribution of brightness within the field of view

Freedom from disturbing glare Spatial distribution of lightSpat a d st but o o g t

General lighting, directional lighting, backlighting and uplighting, diffuse lightingp g g, g g

Light colour and colour rendering Colour temperature and colour rendering index Colour temperature and colour rendering index

Design Factors & Issues

Directional effects (form dimension & texture)Directional effects (form, dimension & texture) Direction and distribution of light within a space

Influence perception of the space Relates partly to desirable illumination levels and partly

to architectural style and visual emphasis Good light design - an appreciation of the nature and g g pp

qualities of the surfaces Modelling ability of light to reveal solid form Modelling ability of light to reveal solid form

Fail to do that will result as bland and monotonous Emphasis e.g. surface texture & characteristics

Examples of directional effects in lighting design

Design Factors & Issues

Glare Occurs when objects, seen directly or by reflection,

are too bright c f the general background

are too bright c.f. the general background

Disability glare - impairs ability to see detail w/o il i i l di f tnecessarily causing visual discomfort

Shift in adaptation level Discomfort glare - causes visual discomfort w/o

necessarily impairing vision Depends on occupants activity, angle of view, size and

brightness of source, average luminance of background

Bright light enteringfrom a window

Veiling reflection fromoverhead light source

Examples of glare and veiling reflection

from a window overhead light source

Examples of glare and veiling reflection

Design Factors & Issues

Reduce glare from artificial light sourcesReduce glare from artificial light sources Limit the luminance of sources in eyes direction

Replace a bright source with few weak sources Restrict light distribution to sideways light to the eye

Screen the sources from view Introduce downstand screens Introduce downstand screens Use screening within the fitting (e.g. louvres) Enclose source in light diffusing panel/fitting Conceal fittings from view (e.g. by beams)

Design Factors & Issues

Reduce glare from artificial light sourcesReduce glare from artificial light sources (Contd) Re-position the work station to avoid glare Raise background luminanceRaise background luminance

Use fittings with more upward flux (brighten ceiling)S if hi h fl t fl Specify higher reflectance floor

Use light-coloured finishes

Design Factors & Issues

Reflected glare & veiling reflectionReflected glare & veiling reflection Bright patches on glossy surfaces from reflection

Reflected glare - produce visual discomfort Veiling reflection - reduce contrast and visibility

May be minimised by: Ensure no part of the task is at or near the mirror angle Ensure no part of the task is at or near the mirror angle

with respect to the eye & bright sourceI li ht f lli id t th i l t k Increase light falling sideways onto the visual task

Use luminaires w/ large surface area & low luminance Use paper, machines, materials etc. with matt surfaces

Glare control for video display unit (VDU)[Source: CIBSE Lighting Code]

Lighting Calculations

To calculate the amount of light that willTo calculate the amount of light that will result from a design Critical for commercial & institutional buildings Seldom required for residential designSeldom required for residential design

Basic considerations Light sources (lamp lumens) Luminaires & light distribution Luminaires & light distribution Initial vs. maintained light levels (as lamps age

and luminaires get dirty, light level drops)

Lighting Calculations

Predict general & ambient light levelsPredict general & ambient light levels Rough estimation based on a Watts/sq.m method

Not very accurate, but good for prelim. planning Lumen method calculations

Average illuminance Good for general lighting Good for general lighting

Point-by-point computer calculations Most complicated, start from fundamental laws Can be used for outdoor lightingg g

Rough estimation based on a Watts/sq.m methodAverage light level desired & Watts/sq m of Watts/sq m ofAverage light level desired & typical application

Watts/sq.m of fluorescent, CFL or

HID lights

Watts/sq.m of incandescent or halogen lamps

25-50 luxHotel corridors, stair towers

1-2 3-7

50-100 luxOffice corridors, parking garages, theatres (house lights)

2-4 7-10theatres (house lights)100-200 luxBuilding lobbies, waiting areas, 4-8 10-20g , g ,malls, hotel function spaces200-500 luxOffice areas, classrooms, lecture halls, conference rooms, ambient retail lighting, workshops

15-25 Not recommended

g g, p500-1000 luxGrocery stores, laboratories, work 12-20 Not recommended

[Source: Adapted from Karlen and Benya, 2004. Lighting Design Basics]

areas, big box retail stores

Lighting Calculations

Lumen Method: average illuminance (E) isg ( )

MFUFNnFE A

E F = initial bare lamp luminous flux (lumens) n = number of lamps per luminaire N = number of luminaires UF = utilisation factorUF utilisation factor MF = maintenance factor

A f th f ( 2) A = area of the surface (m2)

Lighting Calculations

Utilisation factor (UF)( ) Ratio of total flux received by the surface to the

total lamp flux of the installationtotal lamp flux of the installation UF tables are prepared for general lighting with

l f l i i f 3 iregular arrays of luminaires, for 3 main room surfaces: ceiling cavity, walls, and floor cavity or h i t l f lhorizontal reference plane

Maximum spacing to height ratio (SHRmax)p g g ( max) Luminaire spacing shall not exceed the max. to

ensure uniformityensure uniformity

Lighting Calculations

Room index (K): a measure of the proportions of the ( ) p proom, for rectangular room K = (L x W)/(L + W) h K = (L x W)/(L + W) hm

L = length of the room W = width of the room W = width of the room hm = height of luminaire above horiz. reference plane

Eff ti fl t f ili ll & fl Effective reflectances of ceiling, walls & floor Cavity index (CI) = (L x W)/(L + W) h = K x hm/h

h = depth of the cavity (ceiling or floor)

Determine effective reflectance from tables or formulae (see examples in CIBSE Lighting Code)

R d d fl & ill i iRecommended room reflectances & illuminance ratios[Source: CIBSE Lighting Code]

Lighting Calculations

Maintenance factor (MF)Maintenance factor (MF) Ratio of maintained illuminance to initial

ill i (l f l l i )illuminance (losses for lamp lumen maintenance) MF = LLMF x LSF x LMF x RSMF

Lamp lumen maintenance factor (LLMF) Lamp survival factor (LSF) Lamp survival factor (LSF) Luminaire maintenance factor (LMF) Room surface maintenance factor (RSMF)

See CIBSE Code of Lighting for descriptionf g g p

Lighting Calculations

Lumen method: calculation procedure Calculate room index K, floor/ceiling cavity index Calculate effective reflectances of ceiling cavity, walls &

fl itfloor cavity Determine utilisation factor (UF) from manufacturer's data,

using the room index and effective reflectancesusing the room index and effective reflectances Determine maintenance factor (MF) Obtain nos of luminaires required (using lumen method)Obtain nos. of luminaires required (using lumen method) Determine a suitable layout Check that the geometric mean spacing-to-height ratioCheck that the geometric mean spacing to height ratio Check the layout does not exceed SHRmax Calculate illuminance achieved by the final layouty y