I came across this program and like it very much. It changes the "color temperature" of your display to better approximate natural sunlight. You can control how much, and how fast, it changes. Windows, Mac, IOS, and Linux versions, and an Android version in progress.
The main reason I think it is good is there is substantial evidence that blue-rich light keeps us awake at night and affects our internal "clock". You can read more about it on the site, under the "Sleep Research" and FAQ pages, and decide for yourself.
For people who might want to sleep a little easier after reading (or surfing) at night: this might help.