1. Department of Technical Education
Andhra Pradesh
Name
: P. Balanarsimlu
Designation
:Lecturer
Branch
:Electrical Engineering
Institute
:Govt. Polytechnic Nizamabad
Year/Semester
:VI Semester
Subject
:Electrical Utilisation and Traction
Subject Code
:EE605A
Topic
:Electric Lighting
Duration
:100 Mins
:Design & Definitions of Lighting
Sub Topic
:PPT, Diagrams, Animation
Teaching Aids
Revised By : K. Chandra Sekhar, L/EEE, GPT, HYD
9EE605A.9to10 1

2. Recap Calculation of Illumination using Inverse Square Law
In the last class you have learnt about
Calculation of Illumination using
Inverse Square Law
Lambert’s Cosine Law
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3. On completion of this topic you would be able to know
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
9EE605A.9to10 3

4. Definitions Utilization Factor or Co-efficient of utilization
The following are some of the definitions which we come across in the design of electric lighting scheme.
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
9EE605A.9to10 4

5. Definitions 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
9EE605A.9to10 5

6. Definitions 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
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7. 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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8. Definitions 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
9EE605A.9to10 8

9. 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
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10. 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.
9EE605A.9to10 10

11. It’s value varies from 0.5 to 1
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
It’s value varies from 0.5 to 1
9EE605A.9to10 11

12. Definitions 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)
9EE605A.9to10 12

13. Definitions Some of the Examples of Luminous efficiency sl
Type of lamp
Colour
Efficiency 1
Sodium vapour
Yellow
40 to 80 2
Neon
Red
15 to 40 4
Mercury vapour
Bluish white
40 to 80 5
Incandescent
white
10 to 20
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14. It is measured in Watt/candela or Watt/MSCP
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
9EE605A.9to10 14

15. 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 lamps
Space height ratio =
Mounting height of lamp
Its value varies from 0.8 to 1.5
9EE605A.9to10 15

16. Design of lighting scheme
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 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
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17. Given data Utilisation Factor, U. F = 0
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 = Lumen Flux reaching on the working plane, Ø = Total flux X U.F. = x 0.45 = Lumen. Illumination, E = Ø / A = / 108 = 150 Lux Ans.
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18. INDOOR LIGHTING
Fig.1
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19. Design of Lighting Scheme
Problems on Indoor Lighting
Problem 2
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.
9EE605A.9to10 19

20. Coefficient of utilization, UF =0.5
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
9EE605A.9to10 20

21. Flux required on working plane ,Ø
Solution
Total flux =
E x A =
80 x 96 =
7680 lumen
Flux required on working plane ,Ø
Total Flux
7680 = = =
19200 lumen Ø
UF x MF
0.5 x 0.8
Flux,Ø
19200
Total wattage = = =
480 watt η 40
9EE605A.9to10 21

22. Number of 40 watt fluorescent lamps
Solution
Number of 40 watt fluorescent lamps
Total wattage
480 12 = = = 40 40
12 m 3m 3m
8 m
1.5m 1m
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23. 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.
9EE605A.9to10 23

24. Coefficient of utilization, UF =0.5
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
9EE605A.9to10 24

25. Solution Total flux = E x A = 120x390 = 46,800 lumen
Flux required on working plane
Total Flux Ø = x DF UF
46800 = x
1.4 =
1,31,040 lumen
0.5
Flux,Ø
0.5 x 0.8
Total wattage = = η 40 =
480 watt
9EE605A.9to10 25

26. Solution Flux,Ø 131040 Total wattage = = η 40 = 3726 watt
Contd..
Flux,Ø
131040
Total wattage = = η 40 =
3726 watt
Number of 40 watt fluorescent lamps
Total wattage = 80
3726 = 80 =
40.95 =
say 40 lamps
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27. Disposition of Lamps Assuming mounting height = 3m 3
Then space height ratio = = 1 3
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28. Problem 3
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
Lamp Size
100w
200w
300w
Luminous Efficiency 12 15 18
9EE605A.9to10 28

29. Given Data Required 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
9EE605A.9to10 29

30. Solution Flux required on working plane ,Ø E x A = x DF Ø UF 100 x 240
Contd…
Flux required on working plane ,Ø
E x A = x DF Ø UF
100 x 240 = x
1.25
0.5 =
60,000 lumen
9EE605A.9to10 30

31. Solution Number of 100 watt lamps required 60000 = 50 = 12 x 100
Contd…
Number of 100 watt lamps required
60000 = = 50
12 x 100
Number of 200 watt lamps required
60000 = = 20
15 x 200
9EE605A.9to10 31

32. Solution Number of 300 watt lamps required 60000 = 12 = 18 x 300
Contd…
Number of 300 watt lamps required
60000 = = 12
18 x 300
Assuming mounting height as 3m and lamps are 200w
9EE605A.9to10 32

33. Disposition of Lamps 4 space height ratio along length wise = 1.33 = 3
space height ratio along width wise = = 1 3
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34. Summary In this class we have discussed about
Definitions of terms used in design of lighting scheme
Problems on design of lighting
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35. Quiz 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.
9EE605A.9to10 35

36. Quiz 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.
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37. Frequently Asked Questions
Define utilization factor and depreciation factor.
Define reduction factor and space height ratio.
State the factors affecting utilization factor.
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38. Frequently Asked Questions
Problem 1
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
Ans : 36 lamps in 3 rows, 12 lamps in each row
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39. Frequently Asked Questions
Problem 2
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.
Ans : a) 2.9 lux, b) 1.2 lux
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40. THANK YOU
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