I have noticed that when flying at night you can still see everything such as mountains and lakes and stuff, but in real life you can’t see this from a plane without ground lighting, usually there isn’t ground lighting in the mountains and it’s just pitch black.
This would very as it would add realism to the simulator.
I’m not sure making it darker is such a good idea, at night you can hardly taxi as it is…
Jokes aside I believe what Ed said is correct, I’ve noticed some nights are much darker than others.