|slowing light downPage 2 of 2 (1, 2)|
|Forgetting about the elements of light which are lost because of the two-way...either -|
1- your mirrors are perfect, and the light would just bounce around in there forever.
2- your mirrors aren't perfect...not perfectly clean...and so eventually more and more of the light that hits the not-perfectly-clean parts of the surface therefore transform into heat or whatever, until it just gets dark in there. And probably not so warm though.