depends on my mood. both light and dark can be good but the thing is with me, i only like natural light and there isn't such a thing at night (unless you count the moon) i love the dark as it calms me as long as i don't think about a monster or something coming after me (yes im a grown lady and still think that lol. never changed since i was a kid) i love the natural light from outside because it's beautiful and keeps me up. i hate artificial light because its orange/yellow and ugly. i would prefer a blue/white light in my room or non at all. my sweet spot is in the morning when everyone's still sleep i love to turn all the lights off and open the window, sit right near it and work on art, write or other things. i also like it closed with some light coming in and watching movies, shows or videos.
unlike most people, being on my laptop while the room is dark doesn't keep me up, it actually makes me more tired (i was still like this before i gave up on phones)