Question

A point source emitting 628 lumen of luminous flux uniformly in all directions is placed at the origin. Calculate the illuminance on a small area placed at (1.0 m,0 0) in such a way that the normal to the area makes an angle of ${37}^{\circ }$ with the X-axis

Answer 1

$\text{l=Luminous intensity}$

$=\frac{628}{4\pi }=50candela$

$r=1m,\theta ={37}^{\circ }$

$\text{So, illuminance}e=cos\frac{\theta }{r^2}$

$=50\times \frac{cos{37}^{\circ }}{1^2}$

$=50\times \frac{\left(4/5\right)}{1}=40lux$