All of the above:

Can't beat it being cooler. still of the night and there is relatively no wind, maybe a gentle breeze at best. Drunks scare me, tired night shift workers going home or those going to work can be scary too. I generally prefer the dawn head starts for a ride. I also ride street light lit roads, generally go slower and a more casual & safer night ride, but w/ 15-30 minutes head start, you can get well into your longer loop rides. Add that slower and layering clothes really isn't necessary often times in the city, now rural, that can get darn cold. At a certain point of the pre-dawn/post-dusk ride traffic is virtually non-existent, so you can cross a multi lane road easier and safer. Most drivers are still having breakfast or eating dinner when you are doing your thing. Even when I travel by car, I prefer night driving to eliminate traffic problems and pretty much a lot of the reasons for a bike commute. I'm not big on using my brakes if it's not necessary, reduced traffic is the best for that, otherwise you're on the road with drivers that stop for no reason at all. So annoying getting behind someone that keeps hitting their brakes like that. I don't think they realize that every time they do that, every single vehicle behind them has to also, just totally unnecessary stress if they leave safe following distance and actually try to get to where they intend to go ?

Lights, I have are the Wal-Mart $ 20 Zefal brand set to be seen not really to see. I'd need one of those multi-million candle power lights to actually see the road far enough in front of me to generate the kind of speed I do in broad daylight.