A point source emitting 628 lumen of luminous flux uniformly in all directions is placed at the origin. Calculated the illuminance on a small area placed at (10 m, 0, 0) in such a way that the normal to the area makes an angle of 37° with the X-axis.

Given,
Luminous flux = 628 lumen

Angle made by the normal with the x axis
Distance of point, r = 1 m
Since the radiant flux is distributed uniformly in all directions, the solid angle will be
.




Illuminance E is given by:



On substituting the respective values, we get,



So, the illuminance on the area is 40 lux.


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