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Department of Technical EducationAndhra Pradesh

NameDesignationBranchInstituteYear/SemesterSubjectSubject CodeTopicDurationSub Topic

Teaching Aids

: P. Balanarsimlu: Lecturer: Electrical Engineering: Govt. Polytechnic Nizamabad: VI Semester: Electrical Utilisation and Traction: EE605A: Electric Lighting : 50 Mins: Units of wave length & Definitions of light parameters: PPT, Diagrams,Animation

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

Recap

In the last class you have learnt about

• Nature of Light and its Propagation

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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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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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Wave Length

Micron is also used to represent wave length

Wave length ( λ ) =Velocity of light propagation (v)

Frequency (f)

1 Micron ( μ ) = 10-6m

Fig.1

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Definitions

1) 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

One radian = 180 π

radians

degrees ArcRadius

O

Fig.2

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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

ω

are

a

Radius

S

Definitions

Fig.3

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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

timeΦ or F= lumens

Lumen = candle power X solid angle

= c.p. X ω

Definitions

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4)Luminous intensity ( I ) or Candle power (C.P.) It is the luminous flux per unit solid angle in a given direction

Luminous flux

Solid angleI or C.P.= Lumen/steradian or candela

F

ωLumen/steradian or candelaI or C.P.=

Definitions

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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

Area A

F or Φ

Definitions

=

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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)

Definitions

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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

4πM.S.C.P.=

Definitions

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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

2πM.H.S.C.P.=

Definitions

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10)Lamp efficiency It is the ratio of the output i.e luminous flux in lumens

to the electrical power input in watts

Lumen/wattLuminous flux

Electric power Lamp efficiency =

Definitions

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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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0 0

1 8 0 0

9 0 0A

D

B

C

La

mp

ax

is

A

D

B

C0 01 8 0 0

9 0 0

OA

D

B

C0 01 8 0 0

9 0 0

O

Polar Curves

On horizontal plane

On vertical plane

Lamp and horizontal plane

Fig.4aFig.4b Fig.4c

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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

A

D

B

C

La

mp

ax

is

Fig.4a

A

D

B

C0 01 8 0 0

9 0 0

OA

D

B

C0 01 8 0 0

9 0 0

O

Fig.4b

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Horizontal Polar Curves

A

D

B

C0 01 8 0 0

9 0 0

OA

D

B

C0 01 8 0 0

9 0 0

O

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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0 0

1 8 0 0

9 0 0

Vertical Polar Curves

On vertical plane

Fig.4c

• 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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Summary

So far we have discussed about

• Units of Wave Length• Definitions of

• Plane angle

• Solid angle

• Luminous flux

• Luminous intensity

• Illumination

• Brightness

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• M.H.C.P

• M.S.C.P

• M.H.S.C.P

• Lamp efficiency

• Polar Curves

Definitions of

Contd…

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1Q. Lux is the unit of

A) Illumination B) Flux

C) Luminous intensity D) Solid angle

Quiz

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2Q. The unit of lamp efficiency is

A) C.P./Watt B) Watts/ Lumen

C) Lumens/Watt D) Lumens / Steradian

Quiz

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3Q. One radian is equal to_______ degrees.

D) 180/π

B) 360/π

C) π/180

A) 180/2π

Quiz

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4Q. The largest solid angle subtended is ____steradian.

A) π

C) π/4

B) 4π

D) 1/π

Quiz

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1) Define a) Plane angle and b) Solid angle

2) Define Luminous flux and intensity

3) Define Illumination and Luminous efficiency

4) Define M.H.C.P., M.S.C.P. and M.H.S.C.P

5) Draw and explain the vertical and horizontal polar

curves

Frequently Asked Questions

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THANK YOU

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