Department of Technical Education
Andhra Pradesh
Name
Designation
Branch
Institute
Year/Semester
Subject
Subject Code
Topic
Duration
Sub Topic
Teaching Aids
Revised By
: 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
: K. Chandra Sekhar, L/EEE, GPT, HYD
9EE605A.9to10
1
Recap
In the last class you have learnt about
• Calculation of Illumination using
• Inverse Square Law
•
Lambert’s Cosine Law
9EE605A.9to10
2
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
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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4
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
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5
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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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.=
>1
Illumination under normal working conditions
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7
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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8
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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9
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.
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10
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
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11
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)
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12
Definitions
Some of the Examples of Luminous efficiency
sl Type of lamp
Colour
Efficiency
1 Sodium vapour
Yellow
40 to 80
2 Neon
4 Mercury vapour
Red
15 to 40
Bluish white
white
40 to 80
10 to 20
5 Incandescent
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13
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
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14
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
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15
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 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
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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.
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INDOOR LIGHTING
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Fig.1
18
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.
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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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20
Solution
Total flux
=
E x A = 80 x 96
= 7680 lumen
Flux required on working plane ,Ø
Ø =
Total Flux
=
UF x MF
Total wattage
7680
= 19200 lumen
0.5 x 0.8
=
Flux,Ø
η
9EE605A.9to10
19200
=
40
= 480 watt
21
Solution
Number of 40 watt fluorescent lamps
Total wattage
=
480
= 12
=
40
3m
1m
1.5m
8m
3m
12 m
40
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Problems on Indoor Lighting
Problem 3
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.
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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
=
E x A = 120x390 = 46,800 lumen
Flux required on working plane
Total Flux
x DF
Ø =
UF
=
Total wattage
46800
x 1.4 = 1,31,040 lumen
0.5
Flux,Ø
0.5 x 0.8
=
=
η
40
= 480 watt
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Contd..
Solution
Total wattage
=
Flux,Ø
η
=
131040
40
= 3726 watt
Number of 40 watt fluorescent lamps
Total wattage
=
80
=
3726
80
= 40.95 =
say 40 lamps
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Disposition of Lamps
13 m
3m
3m
1.5m
2m
30 m
= 3m
3 =1
= 3
Assuming mounting height
Then space height ratio
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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
Luminous Efficiency
12
9EE605A.9to10
200w
15
300w
18
28
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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Solution
Contd…
Flux required on working plane ,Ø
Ø =
ExA
x DF
UF
=
100 x 240
x 1.25
0.5
= 60,000 lumen
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30
Solution
Contd…
Number of 100 watt lamps required
=
60000
= 50
12 x 100
Number of 200 watt lamps required
=
60000
= 20
15 x 200
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31
Contd…
Solution
Number of 300 watt lamps required
=
60000
= 12
18 x 300
Assuming mounting height as 3m and lamps are
200w
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Disposition of Lamps
12 m
3m
4m
2m
1.5m
20 m
space height ratio along length wise
space height ratio along width wise
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4 = 1.33
= 3
3 = 1
= 3
33
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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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.
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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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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
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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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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THANK YOU
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