The day has a nice rise and fall to it. The sun rises in the morning, it sets at night. Artificial light disrupts that flow. Curtains do it to, closing off the world, putting us in a place that is unnatural.
I think it all started when I had a desk under some skylights instead of artificial lights. It was the only light that came in and I knew when I couldn't see anymore it must be time to go home.
I still do it. At school, early in the morning when it is still dark, I leave the lights off, my computer gives of enough light.
It makes me feel like the day has a rhythm. I don't live in Vegas, I like my days to start, live, and end. I like the dark of the night, it brings comfort, another day coming to an end.