Problem 5.6

An illuminant shaped as a plane horizontal disc $S=100 \mathrm{~cm}^{2}$ in area is suspended over the centre of a round table of radius $R$ $=1.0 \mathrm{~m} .$ Its luminance does not depend on direction and is equal to $L=1.6 \cdot 10^{4} \mathrm{~cd} / \mathrm{m}^{2}$. At what height over the table should the illuminant be suspended to provide maximum illuminance at the circumference of the table? How great will that illuminance be? The illuminant is assumed to be a point source.