I do almost all my cycling in the dark. In the winter it's because it's dark whenever I have time to ride. In the summer, it's because it's too damned hot to ride during daylight hours. Get yourself a good headlight. There are some crazy bright ones, but I find anything over about 200 lumens is adequate for my needs. Get a high quality tail light or two as well. If I have two tail lights, I leave one on in steady mode and put the other one in a blink mode.