Welcome to PF, Xcrunner.
It depends upon how you define 'light'. Anything within the visible spectrum will eventually be depleted, although there might be some tiny spontaneous photon formation. The wood itself will emit infrared based upon its temperature, and higher frequencies such as X-rays won't be blocked.
That's all that I've got; best wait for someone else to provide a better response.
Hmm. Interesting. I wonder if you put mirrors on the inside surfaces, if you could catch the light and keep it in case the lights go out.
Seriously, though, I'm not sure you could close the box before most of the light got out anyway. Light's sort of a slippery substance. Everything Danger said is true, but... I doubt that you'd catch *any* light to begin with, whether it dissipated or not. Particularly not with 2 inch thick wood... even if it were "air tight".
I don't mean visible light. I mean the entire light spectrum... x-rays, gamma rays, visible light, infrared, microwaves, etc. all of them as waves. Obviously there are still those waves when I seal up the box, but will the amplitude of those waves every entirely decrease to zero?
The short answer is 'no'. As mentioned, high-frequency EM won't even notice the walls, and low frequency such as radio will just slide on through as well. Wood is opaque only to visible and near-visible wavelengths.
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?)
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