Well that is a tricky question. It depends on so much, for example the mood you are going for. If it’s dramatic, almost like Batman, it’s more about the darkness than the light. If it’s night and outside with moon, maybe there’s no moon. There’s infinite possibilities and there’s no real formula of put this light there with a strength of 8 and you’re ok. It’s more of trying to get a feel and it’s all about your eye and perception. What I do is, I play around a lot, and I mean a lot. Trying with just a sun lamp with low power and a bit of blue/purple tint. Maybe if it’s a character, he is lit just by a orange lamp in the nigh, maybe on candle light. Maybe there’s fireflies around and you have tiny green bright spots all around. Maybe you have atmosphere and fog which makes the moon light rays visible.
So you have to play around a lot to try and define your look. Don’t be afraid to start over and over. Turn off almost of the lights and turn them on one by one to appreciate their influence in the scene and most of the time you realize you had 10 lights and with 3 was just enough. Try playing around with colors, etc. I did the night version of the Spice Vendor and I went through a lot of iterations.
Here’s the normal day scene:
https://www.youtube.com/watch?v=ANTHeNLNUSQ
And here’s that converted to night:
https://www.youtube.com/watch?v=2oalExV57RU
