I think it would be neat if they made it so that light and darkness has more effect on how well you see and how well enemy mobs can see. Like nibbles says he sees perfectly fine IRL when outside in the dark. But what if nibbles had to go from complete darkness to an area with light then back to complete darkness again? that kind of transition will mess up your natural night vision cause your pupils need time to adjust. Its why your eyes hurt when you wake up at night, go into the bathroom and turn the lights on. Your pupils are fully dilated and that sudden burst of light hurts, but your pupils gradually close letting less light in and then making it not hurt so much.

It would also be nice if there was also some tactical advantage to having lights. Sneaking up on a mob in a poorly lit area and hitting them with a high power flashlight can dazzle them. Or better yet what if mobs also reacted to your pipboy flashlight? that one would probably have to be a game option that you can turn off/on though cause it might be too hardcoe for some players. Also if at night with no moon out, the game was a looooot darker maybe that could give the devs or modders an excuse to add in night vision goggles or make it a standard feature/toggle in power armor helmets. Maybe also add in FLIR with white-hot/black-hot, or Predator vision or something like that.

In Fallout 3 there is a mod (Martigens Mutants Mod?) that introduces a lot of new NPC models and numbers of foes, and behaviours and so on... anyway, one thing that this mod added was Night Ghouls. They run like cheetahs on crack, and they have glowing eyes that vary from red to green to yellow to white, etc...

At night, in the distance, you will sometimes see a cluster of these lights ---- looks like a party! Yeh, a party of twelve night ghouls who will swarm over you in a terrifying wave! I don't recall ever seeing them during the DAY, though. At night, they certainly changed the way I behaved... considering how fast they were, I kept an alert eye on the horizon for their tell-tale glowing eyes, because where you see one, there are others nearby and they move F.A.S.T.

Having different foes at night would be great, in short. So long as we can actually SEE them (actually ~bumped~ into a ghoul in the metro once because I had my light off to avoid alerting foes as I was sneaking: scared the beeejeesus out of me).

If you want to go with realism, after the post nuclear apocalypse there would be very little light pollution. essentially making things extremely brighter during full moons, and much darker during new moons. I agree though, it would add a very interesting game mechanic if they could capture this lighting perfectly. My vote is to do whatever is realistic in a post nuclear apocalypse environment

It would be pretty spooky.

For the raiders, I mean. They'd be out in the darkness and see a small glimmer of light nearby, approaching them slowly. They'd sigh in relief, not knowing that it was the light from a power armor helmet.

I remember Fallout 3 having some dark nights.