Page 326 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Steradian
Steradian is the unit of solid angle. One steradian is defined as the solid angle that is subtended at the centre of
a sphere by its surface having area equal to radius square,
ω = area of surface/ square of radius
= A/ r² steradians

Candale power
The light radiating capacity of a source is called its candle power. The number of lumens given out by a source
per unit solid angle in a given direction is called its candle power. It is denoted by C.P.
Total flux emitted = CP x solid angle
= 1 X 4p = 4p lumens
= 4 p lumens
Luminious intensity

Luminous intensity in any particular direction is the luminous flux emitted by the source per unit solid angle in
that direction. It is denoted by i and its unit is candela or candle power (CP) .Luminous intensity of source in a
particular direction, I = φ / ω
Illumination
When light falls on a surface, it becomes visible, the phenomenon is called as illumination.
It is defined as luminous flux falling on a surface per unit area. It is denoted by E and measured in lumen per
square meter or meter- candle .
E = Ф / A lux
LUX
One-meter candle or lux is defined as the illumination produced by a uniform source of one CP on the inner
surface of a sphere of radius one meter.

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CITS : Power - Electrician & Wireman - Lesson 54-59