f.lux adapts the color of your computer's display to the time of day. It makes it eye-friendly at night and bright like sunlight during the day. f.lux makes your computer screen look like the room you're in, all the time. When the sun sets, it makes your computer screen to be no brighter than the indoor lights. In the morning, it makes things look bright again. Put in the info about what kind of lighting you have, and where you live - this is all needed for the program to work the right way. The control over your PC display color tone is performed automatically by f.lux.