Totally depends on the place/space. Rural roads seem safe until you hit a critter or until you encounter the teenage(minded) dimwit doing 80+mph in a 45 b/c "no one is out there anyway." Good luck having any kind of lighting save you from that horror. Urban riding on roads you generally encounter a ton of cell-attached, chemically altered drivers. No fun, and not safe. Basically, night riding can be "safe" but with little to no room for error (on your part or the drivers') mixed with the likelihood of encountering unsafe traffic (drinkers, druggers, sleepy heads, bad night vision etc) means when things go wrong they generally go VERY, VERY wrong. Take that as anecdotal/experiential evidence from a longtime cyclist and former EMT.

All factors taken into account, day riding is IMHO WAY safer by every measure. That said, do my rides start/end in the dark at times... yes.