Light in a sphere

If you put light inside a sphere, and the sphere was made out of reflective material - the light should bounce around it forever, right?

What would happen if you shinned a lazor in it? More and more light would get added,

Even if photons get reflected, the intensity of the reflection would be less than that of its source due to the multiple deflections. Light is only a photonic emanation, not something that will just go on forever. If you put a mirror on earth and make it visible to the stars, will the stars receive the same light back which they themselves emitted? Obviously not. The distances between mirrors within the sphere would have to be small in order to just carry such a reflection of light, but because there is distance, photons loose momentum.
No? Make a sphere of mirrors pass light into it and stop the source, what happens to the light inside the sphere? It eventually stops just as it source has. It's that simple.