I've been doing the dark backgrounds for years, due to being farsighted. I recently switched to a high-contrast theme, and it is way easier on the eyes. I think not all dark themes are equal when it comes to amount of work the eye muscles have to do.
I see, kinda ;) I musn't grumble about my condition, just thought it relevant that its quite possible to try working in a dark background to see if it affects sleep cycle.
