Even with windows, and candles nearby, some rooms are pitch-black, like if you half a mile down a mineshaft:
People’s eyes adjust to darkness pretty well, and you can see a lot from even a few photons of light. But even adjusting my brightness up, I can’t see even the most basic of shapes.
This makes it totally impossible to interact with the environment at night. I assume that’s a bug, since being able to be a thief and rob people at night appeared to be part of the game’s design.