I installed f.lux on my computers Friday night, and my eyes and brain immediately felt better. I did not feel eye strain go away, as some people describe, but felt more relaxed and tired (as I was! it was late and I was feeling like going to bed!). It was soothing.You can read comments about it, pro and con, on Macupdate, idownloadblog, PCWorld, and etny.
I have known about it for a long time, but only recently tried it out. Links to scientific research on light and sleep are provided on their site.