Earlier this week I reformatted my hard drive and it took all of 30 seconds of running a clean OS to hit me: looking at the screen at night I was almost fucking blinded. I'd gotten so used to fl.ux It was literally painful not to have it.

fl.ux is a tiny app that sits in your menu bar that based on your location slowly starts changing the brightness and temperature of your monitor with the current time of day. 

It's way easier to just try it (it's FREE) than read my half assed explanation. It's one of a handful of apps I can't use a computer without.