An illuminant shaped as a plane horizontal disc of raiud `R = 25 cm`  is suspended
Channel: Doubtnut
Date: 2020-08-16

An illuminant shaped as a plane horizontal disc of raiud `R = 25 cm`  is suspended over a table at a hight `h = 75 cm`. The illuminance of the table below the cnetre of the illuminant is equal to `E_(0) = 70 Ix`. Assuming the source to obey Lambert's law, find its luminosity.