Adjust you monitor first. Most are in Torch Mode so everything is too bright. With my monitor, the nights are dark enough for me, but I can see where some might want it darker.
http://www.imaging-resource.com/ARTS/MONCAL/CALIBRATE.HTM
I am starting to think that people who make darker nights mods don't do this first as every mod I have tried makes it impossible to see the hand in front of my face. For me, its a game, and I need to see. Plus, it ain't that dark out at night as some of these mods make it.
Realistic Lighting Overhaul is one that I use, but I don't know if it works outside. It does make some interiors too dark for me, but most are nicely done. This one may have an outdoor version.