Solution:
Solution

Luminous intensity, L = 20 Cd
Distance of source from center of table, h = 40 cm
Distance of center of table to midpoint of side of table = a/2 = 30 cm
Total distance between source and point, d = $$\sqrt{(h^{2}+(a/2)^{2})}$$ = 50 cm
As per attached picture Cos (theta) = 4/5
Lambert's law, $$I = L Cos \theta / d^{2}$$
$$\rightarrow I = 20 (4/5) / (0.5)^{2}$$
$$\rightarrow I = 64 lux$$