F.lux is a utility designed to help you sleep better at night. Basically, it changes the color temperature of your screen depending on the time of the day and when you wake up. Research has shown that the amount of blue light emitted from standard displays is bad for your ability to sleep late at night; however, the blue light is good during the day. The standard display's color temperature is about 6500K. For reference, daylight is about 5500K, an incandescent bulb is about 2700K, and a candle is about 1900K.