There are quite a lot of people in my department who work in the dark - sounds strange, but they turn off all the lights apart from their desk one. I remember doing this in my undergrad and it made me feel more focused on the work. But I also remember my dad saying its really bad for your eyes!

I just wondered what everyone else does

Sometimes I like to have just my desk lamp and another lamp on. Means the rest of the room is dark but my area is completely well lit. The perfect non-eye-hurting focus-inducing compromise. Maybe that's why I get better work done after dark. Hmmn.