For my money, if you catch visible light in a box, it's going to dissipate fairly regularly. In a classical sense, it will probably taper off to zero asymptotically; quantum mechanically, I guess, it may reach a point where (a) it just bounces around forever (no atoms in the wood absorb it because it's the wrong frequency or something) (b) it eventually is all gone (every photon eventually gets absorbed and emitted on the inside of the wood / outside of the box) (c) some crazy thing in between or (d) something completely and qualitatively different than anything I described above.
For my money... signal diminishes to zero, or so close to zero that you may as well assume it's zero. The point being, of course, is you can't carry light around in a box with you (maybe I'm wrong?)