f.lux adjusts your display based on time of day to avoid getting too much of the wrong light spectrum. Using an ultra-bright cool temperature display late at night not only disrupts sleep patterns, but is hard on your eyes — and with f.lux (OS X, Windows, and Linux binaries available) running, you’ll be gradually slipped into warmer colors as the night goes on.
The only caveat I have about using f.lux is that if you forget it’s running in the evening while you’re editing photos or video, you can get some unintended results. Thankfully, there is also an Alfred workflow I use to smack a hotkey and “snooze” f.lux for a while or enable/disable it entirely.
Alfred is for OS X and a fantastic utility for automation, I don’t know if there is a similar widget for non-Mac environments or not.