Question

The luminous intensity of a light source is $300Cd$. The illuminance of a surface lying at a distance of $10$ $m$ from it will be if light falls normally on it

• A. $30$ lux
• B. $3$ lux
• C. $0.3$ lux
• D. $0.03$ lux

Answer 1

The correct option is B $3$ lux

Illuminance ($E$) is measured in lux. The lux is an SI unit used when characterizing illumination conditions of a surface:
$E=\frac{I}{R^2}lux$
where $I$ is the luminous intensity and $R$ is the distance.
Given $I=300cd$ and $R=10m$
$⟹E=\frac{300}{{10}^2}=3lux$