Lights, if not required by law, are always a good idea when on the road. The odds of you actually being hit by a driver from behind are really quite small, however - particularly if you're riding predictably and legally. The most revolutionary thing I ever learned when riding in traffic was to take my lane. I feel much, much safer in a lane than in the gutter or bike(trash) lane and I get remarkably little aggression from drivers. The upshot to this, of course, is making sure that you obey EVERY rule of the road.
There's always the risk of an accident or a distracted driver, of course. But if you're riding safely and making appropriate precautions for visibility you should be in good shape.