Exactly what I was thinking, I am not a fan of camp fires on every floor, and it would be nice on the wall and outside in the night.
I'm all for oils lamps! They should also have hooks and stuff that you can nail into walls and hang the lamps onto. The lamps should be able to last quite a bit of time to before they need more oil. This way, I can light up my base without needing those damn campfires...
Edited:
Sounds like a good idea, that way it's not too OP. If it took a few days time then I wouldn't see a problem with that.
I like this idea as well, pigs have a lot of fat and that can be refined to make oil in real life,so why not use that to make a light source that lasts a long time. for realism though, i think it should take some time to do this because turning fat into oil takes time