Sealed or darkened windows?

[Mytran]

...didn't look as if it would have been there before...

That's pretty much my suspicion!
It's been a while since I saw the ep, but I seem to remember the window being in an impossible place - as in his bed alcove actually goes through the same wall!

 

[kent]

actually the windows on federation ships having a process that can tint them at the desire of whoever is in the quarters, or automatically in the public areas. it's like reading glasses that tint when sunlight hits them.

 

[RapidNadion]

To address the darkening effect seen in "The Child" ... I seem to recall the effect being clearly a post-production move, rather than an on-set practical "shade." The dimming does happen in a top-to-bottom motion, but even as the virtual shade is descending, the starfield below it is already fading to grey. So I always took that as the transparent aluminum changing its characteristics to become opaque, rather than a metal hatch sliding into place.

We already have this opaque/transparent glass technology, too - it's starting to make its way into "green" office buildings, and has been in many rich folks' shower doors for years.