f.lux is a freeware utility that changes the color of your computer screen to adapt to specific times of the day by adjusting light tones.
What this utility effectively does is makes your screen take the time of day into account and adjust itself accordingly. For instance, when the sun is setting, the screen will dim to a more warm light setting, and then conversely, when the sun is rising in the morning, your screen will brighten up.
A bright computer screen could be part of the reason you're staying up too late or experiencing eyestrain. Using f.lux can assist in balancing out those day/night rhythms and possibly help you sleep better. You can set f.lux to match the kind of lighting you have, and where you live, and it will do the rest, automatically.