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Department of Technical Education Andhra Pradesh

NameDesignationBranchInstituteYear/SemesterSubjectSubject CodeTopicDurationSub TopicTeaching Aids

: P. Balanarsimlu:Lecturer:Electrical Engineering:Govt. Polytechnic Nizamabad:VI Semester:Electrical Utilisation and Traction:EE605A:Electric Lighting :100 Mins:Design & Definitions of Lighting :PPT, Diagrams, Animation

Revised By : K. Chandra Sekhar, L/EEE, GPT, HYD

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Recap

In the last class you have learnt about

• Calculation of Illumination using

• Inverse Square Law

• Lambert’s Cosine Law

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Objectives

On completion of this topic you would be able to know

• Definitions of terms used in design of lighting schemes.

• Design of Lighting Scheme for

• Drawing Halls• Assembly Hall• Factory

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Definitions

The following are some of the definitions which we come

across in the design of electric lighting scheme.

1. Utilization Factor or Co-efficient of utilization It may be defined as “the ratio of total lumens received

on the working plane to the total lumens emitted by the

light source”.

i.e. Utilization factor =

Lumens received on the working plane

Lumens emitted by the lamp

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Factors affecting the utilization factor

• Type light fitting • Colour, surface of walls and ceiling• Mounting height of lamps• Area to be illuminated

It’s value lies between 0.4 and 0.6 for direct fittings it varies from 0.1 to 0.35 for indirect fittings

Definitions

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2. Depreciation or Maintenance factor

It may be defined as “the ratio of illumination under

normal working condition to the illumination when every

thing is clean or new”.

Illumination under normal working conditions

i.e. D.F = Illumination when every thing is clean.

It’s value will be between 0.6 to 0.8

Definitions

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Definitions

Depreciation of illumination is due to the accumulation

of dirt and dust on the lamp. Frequent cleaning of lamp

improves the depreciation or maintenance factor

It is also given as

Illumination when every thing is clean. D.F.= Illumination under normal working conditions

> 1

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Definitions

3. Waste light factor

• when a surface is illuminated by a number of lamps, there is certain amount of wastage due to overlapping of light waves.

• It’s value varies between 1.2 to 1.5.

Area x illumination x waste light factor

Total lumens = Utilisation factor x depreciation factor

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Definitions

4. Reflection factor or Co-efficient of reflection

It may be defined as “the ratio of luminous flux leaving the

surface to the luminous flux incident on it”.

Reflected light

Reflection factor =

Incident light

It’s value will be always less than 1

9

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Definitions

5. Reduction factor or spherical reduction factor

It may be defined as “ the ratio of mean spherical candle

power of a source to its mean horizontal candle power.

M.S.C.P.

Reduction factor =

M.H.C.P.

10

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Definitions

6. Absorption factor When the atmosphere is full of snow or smoke

fumes, it absorbs some light

Hence absorption factor may be defined as “the ratio of net lumens available on the working plane after absorption to the total lumens emitted by the lamp”

Net lumens on working surface Absorption factor = Lumens emitted by the lamp

11

It’s value varies from 0.5 to 1

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Definitions

7. Luminous efficiency or specific out put

• It may be defined as “the ratio of number of lumens

emitted to the electric power in take of a source”

• it’s unit is lumen/watt (lm/W)

12

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10 to 20whiteIncandescent 5

40 to 80Bluish whiteMercury vapour 4

15 to 40RedNeon2

40 to 80YellowSodium vapour1

Efficiency ColourType of lampsl

Definitions

Some of the Examples of Luminous efficiency

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Definitions

8. Specific energy consumption

It may be defined as “the ratio power input to the light

source to its luminous intensity”.

It is measured in Watt/candela or Watt/MSCP

power input to a lamp

Specific consumption =

Luminous intensity of the lamp

14

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Definitions

9. Space height ratio It may be defined as “the ratio of the horizontal distance between the lamps to the mounting height of the lamps above working plane”.

Space between lampsSpace height ratio =

Mounting height of lamp

Its value varies from 0.8 to 1.5

15

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Problem 1

A room 9m x 12m is illuminated by twelve 100watt lamps. The luminous efficiency of the lamp is 30 luminous/watt and the co-efficient of utilization as 0.45. find the average illumination.?

Given data

Room dimensions = 9m x 12m

Wattage of each lamp, P=100 watts

No. of lamps=12

Luminous Efficiency=30 lumens/watt

Design of lighting scheme

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Given data

Utilisation Factor, U.F = 0.45

Required data

Average Illumination, E =?

Solution

Area = 9 x 12 = 108m2

Total wattage = 100 x 12 = 1200 w

Total flux = 1200 x 30 = 36000 Lumen

Flux reaching on the working plane, Ø = Total flux X U.F.

= 36000 x 0.45 = 16200 Lumen.

Illumination, E = Ø / A = 16200 / 108 = 150 Lux Ans.

17

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INDOOR LIGHTING Fig.1

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Design of Lighting Scheme

Problems on Indoor Lighting

A Hall 12mx8mx4m is to have direct lighting giving illumination of

80 lux on the working plane 70 m above the floor. Co-efficient of

utilization of 0.5 and maintenance factor 0.8. Find the number of

fluorescent tube lamps required and their rating. Lamp efficiency

may be taken as 40 lumen/watt. Assume suitable space height

ratio and draw the layout.

Problem 2

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Given Data

Area, A= 12x8 = 96 m2

Illumination, E = 80 lux

Coefficient of utilization, UF =0.5

Maintenance factor, MF = 0.8

Lamp efficiency = 40 lumen/watt

Required Data Number of fluorescent lamps ?

Rating of fluorescent lamps ?

Draw the layout

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Solution

Total flux

Flux required on working plane ,Ø

= E x A 80 x 96 7680 lumen = =

7680

0.5 x 0.8

Total Flux

UF x MFØ = = = 19200 lumen

Total wattage Flux,Ø

η

19200

40 480 watt = = =

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Solution

Number of 40 watt fluorescent lamps

= Total wattage

40

480

40

12 = =

12 m

8 m

1m

3m

3m

1.5m

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Problems on Indoor Lighting

A drawing hall 30mx13m with ceiling height of 5m is to be

provided of with general illumination of 120 lux. Taking

coefficient of utilization of 0.5 and depreciation factor as

1.4, determine the number of fluorescent lamps required,

their spacing, mounting height and total wattage. Luminous

efficiency of 80 W fluorescent lamp is 40 lumen/watt. Show

the disposition of lamps with sketch.

Problem 3

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Given Data

Area, A= 30x13= 390 m2

Illumination, E = 120 lux

Coefficient of utilization, UF =0.5

Depreciation factor, DF = 1.4

Lamp efficiency = 40 lumen/watt

Required Data

Number of fluorescent lamps ? Rating of fluorescent lamps ? Spacing and mounting height

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Solution

Total flux

Flux required on working plane

= E x A 120x390 46,800 lumen = =

46800

0.5 x 0.8

Total Flux

UF Ø =

= = 1,31,040 lumen

Total wattage Flux,Ø

η

0.5

40 480 watt =

= =

DF x

1.4 x

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131040 Total wattage

Flux,Ø

η 40 3726 watt =

= =

Number of 40 watt fluorescent lamps

= Total wattage

80

= 3726

80

= 40.95 = say 40 lamps

Contd..Solution

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Disposition of Lamps

3m

3m

1.5m

2 m

30 m

13 m

Assuming mounting height = 3m

Then space height ratio = 33 = 1

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• A hall 20mx12mx4m is to be illuminated with incandescent

lamps of average illumination of 100 lumens/m2 on working

plane. Find the number, size and mounting height of the lamps.

Show the disposition of the lamp. Assume the depreciation

factor and utilization factor as 1.25 and 0.5 respectively. Take

the space height ratio as 1

Problem 3

Lamp Size 100w 200w 300w

Luminous Efficiency 12 15 18

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Given Data Area, A = 20x12 = 240 m2

Illumination, E = 100 lux

Coefficient of utilization, UF =0.5

Depreciation factor, DF = 1.25

Lamp efficiencies = 12, 15, and 18

Required Data Number of incandescent lamps ? Rating of incandescent lamps ? Disposition and mounting height

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Flux required on working plane ,Ø

E x A

UF Ø = DF x

100 x 240

0.5 = 1.25 x

60,000 lumen =

Contd…Solution

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Number of 100 watt lamps required

60000

12 x 100 = = 50

Number of 200 watt lamps required

60000

15 x 200 = = 20

Contd…Solution

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Number of 300 watt lamps required

60000

18 x 300 = = 12

Assuming mounting height as 3m and lamps are 200w

Contd…Solution

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Disposition of Lamps

3m

4m

2m

1.5m

20 m

12 m

space height ratio along width wise = 33 = 1

space height ratio along length wise = 34 1.33 =

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Summary

In this class we have discussed about

• Definitions of terms used in design of lighting

scheme

• Problems on design of lighting

34

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1) The ratio of the illumination on a surface under normal conditions to that of ideal conditions is called

A) Utilization factor.

B) Reduction factor.

C) Depreciation factor.

D) Reflection factor.

Quiz

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2) The ratio of the total lumens received on the working plane to the total lumens emitted by the light source is

A) Utilization factor.

B) Reduction factor.

C) Depreciation factor.

D) Reflection factor.

Quiz

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Frequently Asked Questions

1. Define utilization factor and depreciation factor.

2. Define reduction factor and space height ratio.

3. State the factors affecting utilization factor.

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Frequently Asked Questions

• A minimum illumination of 80lux is required in the

factory shed of 50mx12m. Calculate the number, the

location and wattage of the lamp used. Assume that the

depreciation factor is 0.8, coefficient of utilization is 0.4

and the efficiency lamp is 14 lumen/watt

Problem 1

Ans : 36 lamps in 3 rows, 12 lamps in each row

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Frequently Asked Questions

39

• In street lighting scheme, lamps having luminous

intensity of 100 candela are hung at a height of 6m. The

distance between two lamp posts is 16m. Find the

illumination under the lamp and at center in between the

lamp posts.

Problem 2

Ans : a) 2.9 lux, b) 1.2 lux

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THANK YOU