Dear Friends, My longtime pending doubt here...! When we focus a mirror on the wall we get bright spot of the light. Ok. Now say, there is cube 6" x 6" x 6" whose inner walls are of mirror surfaces and opaque surfaces are the outer surfaces of the cube. In the center of the cube, in the mid space, I install a lamp (say 100W electric bulb). There are mutiple reflections happening since all the 6 walls are facing each other. Now If I introduce an instrument to measure the intensity or brightness of the light, How much it will be? 2 times, 3 times or 4 times or infinity? But I feel the answer as the "intensity will be same as that of the light at the given distance". It wont get multipled. Still I want an detailed explaination with convincing reasons. Anybody to explain me please!?