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
: 50 Mins
Sub Topic
: Units of wave length &
Definitions of light parameters
Teaching Aids
: PPT, Diagrams,Animation
Revised By : K.Chandra Sekhar, L/EEE, GPT, HYD
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2. Recap In the last class you have learnt about
Nature of Light and its Propagation
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3. Objectives On completion of this topic You would be able to know
The Units of Wave Length
Definitions of the terms used in Lighting
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4. Wave Length
Since wave lengths of light are very small , “Angstrom unit” is chosen (AU or AO) as the unit of wave length
Angstrom unit (AU or AO) =10-7 mm
=10-8 cm
=10-10m
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5. Wave Length Micron is also used to represent wave length
1 Micron ( μ ) = 10-6m
Wave length ( λ ) =
Velocity of light propagation (v)
Frequency (f)
Fig.1
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6. Definitions Plane Angle ()
A plane angle is the angle subtended at a point in a plane by two straight converging lines OR
When two straight lines lying in the same plane meet at a point, the angle between these converging lines at that point is know as “plane angle”
Arc
Radius 
Arc
Radius O
Fig.2
radians
 =
180 π
degrees
One radian =
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7. Definitions
2) Solid angle (ω)
A solid angle is the angle subtended at a point in the space by an area and is the angle enclosed In the volume formed by an infinite number of lines lying on the surface of the volume and meeting at the point
Solid angle(ω) = area/(radius)2 = A/r2 steradian
area S ω
Radius
Fig.3
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8. Lumen = candle power X solid angle
Definitions
3)Flux or luminous flux (Φ or F)
It may be defined as “ the rate of energy radiated in the form of light waves by a luminous body”
Radiant energy
time
Φ or F=
lumens
Lumen = candle power X solid angle
= c.p. X ω
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9. Definitions 4)Luminous intensity ( I ) or Candle power (C.P.)
It is the luminous flux per unit solid angle in a given direction
Luminous flux
I or C.P.=
Lumen/steradian or candela
Solid angle F
I or C.P.=
Lumen/steradian or candela ω
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10. Definitions 5) Illumination ( E ) =
Illumination of a surface is defined as the luminous
flux received by the surface per unit area
It is represented by the symbol E and is measured in
“lux” (or meter candle or lumen/m2).
Illumination E =
Flux
F or Φ =
Area A
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11. Definitions 6)Brightness (B or L)
It is defined as the luminous intensity of the lamp per unit projected area of either light source or the reflecting surface
B or L = I/A cd/m2
I=luminous intensity (candela)
A= Projected or normal area (m2)
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12. Definitions 7)Mean horizontal candle power (M.H.C.P.)
Is the average candle power in the horizontal plane passing through the luminous center of the lamp
8)Mean spherical candle power (M.S.C.P)
Is the average candle powers in all directions and in all planes emitting from the source of light
Total flux 4π
M.S.C.P.=
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13. Definitions 9) Mean horizontal spherical candle power (M.H.S.C.P.)
It is the mean of candle powers in all directions above or
below the horizontal plane passing through the source
of light. (usually lower part)
Total flux emitted in hemisphere 2π
M.H.S.C.P.=
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14. Definitions 10)Lamp efficiency
It is the ratio of the output i.e luminous flux in lumens
to the electrical power input in watts
Lamp efficiency =
Luminous flux
Lumen/watt
Electric power
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15. Definitions 11.Polar Curves
The luminous intensity or candle power is not uniform in
all directions, due to its unsymmetrical shape and design
It is essential to know exactly how the light is distributed
and is usually given in the form of polar curves
Polar curve is defined as a graph representing the
light distribution of a lamp (luminous intensity) in a
horizontal or vertical plane
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16. Lamp and horizontal plane
Polar Curves
Lamp and horizontal plane
On horizontal plane
On vertical plane
Fig.4b
Fig.4c
Fig.4a
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17. Horizontal Polar Curves
Fig 4a shows an incandescent lamp. If the luminous intensity is measured in a horizontal plane about a vertical axis, a curve is plotted between luminous intensity and the angular position as shown in Fig 4b
Fig.4a
Fig.4b
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18. Horizontal Polar Curves
Fig.4b
The drop in luminous intensity along OC at 00 of horizontal polar curve is due to break in the filament where the current enters and leaves
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19. Vertical Polar Curves On vertical plane
Fig.4c
On vertical plane
If the luminous intensity is measured in a vertical plane at various angles, a polar curve in a vertical plane is obtained
The drop or depression in luminous intensity at 1800 of vertical polar curve is due to the position of the lamp holder
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20. Summary Units of Wave Length So far we have discussed about
Definitions of
Plane angle
Solid angle
Luminous flux
Luminous intensity
Illumination
Brightness
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21. Definitions of M.H.C.P M.S.C.P M.H.S.C.P Lamp efficiency Polar Curves
Contd…
Definitions of
M.H.C.P
M.S.C.P
M.H.S.C.P
Lamp efficiency
Polar Curves
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22. Quiz 1Q. Lux is the unit of A) Illumination B) Flux
C) Luminous intensity
D) Solid angle
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23. Quiz 2Q. The unit of lamp efficiency is A) C.P./Watt B) Watts/ Lumen
C) Lumens/Watt
D) Lumens / Steradian
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24. Quiz 3Q. One radian is equal to_______ degrees. A) 180/2π B) 360/π
C) π/180
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25. Quiz 4Q. The largest solid angle subtended is ____steradian. A) π
C) π/4
D) 1/π
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26. Frequently Asked Questions
Define a) Plane angle and b) Solid angle
Define Luminous flux and intensity
Define Illumination and Luminous efficiency
Define M.H.C.P., M.S.C.P. and M.H.S.C.P
Draw and explain the vertical and horizontal polar curves
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27. THANK YOU
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