Page 325 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Terms used in illumination
1 Light
2 Luminous flux

3 Lumen
4 Plane angle
5 Solid angle
6 Steradian
7 Candle power

Luminous flux
The total quantity of radiant energy per second responsible for visual sensation from a luminous body is called
luminous flux.

It is represented as f of ø and measured in lumens

Lumen
It is the unit of luminous flux. One lumen is defined as the luminous flux emitted per unit solid angle from a point
source of one candle power.
Solid angle
The angle subtended by the partial surface area of a sphere at its centre is called as solid angle. It is measured
in steradians and equal to the ratio of area of the surface to the square of radius of sphere,
ω = area of surface/ square of radius
= A/ r² steradians

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