Ambient lights are bad they flatten everything out. Use a strong directional light and then use points/spots for some bounce light (not a lot though as the moon is weak compared to the sun). Make it very contrasty so thatthere is a big difference bewteen light and dark in the image and tint your lights blue (It's not how it is in real life but it's what makes everyone think it's at night)
Alan
Technical Director - Framestore
Currently working on: Your Highness
IMDB