Above the polar circle where I live, we have light all summer, and darkness all winter. Yeah, it has a huge impact on mood. The older I get, the more difficult it gets to deal with imo. I don't know what it is about sunlight but I can look out of the window, and if it's good weather outside, it just makes me happy for no apparent reason. I don't think the darkness depresses you, I think the lack of that positive feeling several times a day whenever you look at the sun and think "Gee, this is a beautiful day" makes all the things you normally have to deal with a bit more daunting, which in turn gives the impression that you are feeling more depressed, and it seems to have to do with the darkness.
