As day goes to night, some inside areas indirectly lit up by the sun will also get darker, but it won't be as drastic (like indoor lightning). Also, if there are any torches outside, they should only be lit during the night. Maybe you could activate the torches outside around dusk when it gets dark enough (but not pitch black). They'll stay lit until about halfway through dawn.
Also, how about adding certain NPCs that would only appear at night (vampires and other undead, thieves, people who work at night, etc.) or during the day (town defenders if any, most normal citizens, etc.)?