Krish Raghav, my esteemed colleague, blogs about the most useful freeware application I have used in a while. Called f.lux, the app sits on your desktop and tries to match the lighting on your computer monitor to the ambient light around you. Thereby, I assume, reducing strain on your eyes. Most excellent. All you need to do is tell it what type of lighting you have and where in the world you live. The app will take care of the rest. Most highly recommended.