The most effective software you can download aren't always complex in their operation. For me, good software is simple,no steep learning curve, yet effective. Same can be said about F.lux, simple to use yet extremely effective.
What is F.lux? Its a computer program that adjusts the temperature color within your display. The sole purpose of the software is to reduce eye strain during evening hours and improve your sleep cycle.
How it works is simple, once you have installed the software, you can choose a location based on geographical coordinates, or you can choose to use your Zip code and name of location. F.lux will then calibrate your computer's display's color accordingly to the time of day, all based on sunrise and sunset at your place of location. Once at sunset, you'll notice a gradual change in the color temperature which then has a much warmer hue and the display will restore back to its original color at sunset.
Simple software, easy installation and practically works itself. F.lux is available for Windows, OS X and Linux and its free.