It doesnt get dark enouhg at night, and caves arnt that dark either, i really dont ever use a light source! Would like to see that change, have caves and many dungeons to be extemely dark so having a light or some kind of night vision (could play an alignment role) It would add extra danger to dungeons and the night if with a weak light spell or torch you could not fully see what was on your screen. Better torches could also be crafted by carpenters :P

Could play a good role in alignment, all Evil characters get a -5 stat penalty during day (while outside) but recieving night vision for seeing better at night and a +10% speed boost at night.

Nightfall would be the time for Evil to hunt, it would be easy, just look for the light sources.