Lots of flashlights will. Ditto with DIY and good bike-specific lights (Dinotte, Lupine, etc). With the right lights, riding at night is just as easy as riding in the day.
This is basically going to turn into a thread full of A.) people afraid to go faster than 20 mph, and B.) people with real light rigs who don't think twice about it.
Or C.) People that can't go faster than 20 mph anyway
Actually there's probably a lot different circumstances that would affect how fast one feels comfortable going at night (or day for that matter):
Busy well lit roads
vacant well lit roads
MUPs
badly lit roads in good condition
badly lit roads in bad condition
streets with lots of intersections
streets with lots of pedestrians, etc.
I ride slower at night. I'm not sure how much slower since it's too dark to read my cyclocomputer. I drive more cautiously at night when I'm in my car too.
It's not just the road hazards, it's the ninjas and the sneaky critters. I may miss the guy who's been sitting in his car for twenty minutes and is now about to door me.
I don't care how bright your lights are, it's not sunlight. You can't get the big picture like you can during the day.
It's not that I would rule out going 30 at night depending on where I was so I guess my MAX speed may not be affected but my average speed sure is.