Question

The illuminance on a surface is 6 lux and the surface is 4 meters from the light source. What is the intensity of the source?

A. 24 candelas
B. 144 candelas
C. 72 candelas
D. 96 candelas

Answer 1

Answer: D. 96 candelas

Explanation: Illuminance is defined as the quantity of light incident on a surface per unit of area. It depends on the light’s intensity and its distance from the surface.

E=  illuminance on the surface (in lux)= 6 lux

I =  the intensity of the light from the source (in candelas) = ?

S= distance from the light source to the surface (in meters) = 4 m

$E=\frac{I}{S^2}$

$I=E\times S^2$

$I=6\times (4)^2=96candela$