CF.lumen changes the colors of your Android device's display based on the position of the sun. With the default settings, your display will get a warmer tint (lower color temperature) when the sun is down, to look more like indoor lighting and less like the sun, which causes less strain on your eyes and doesn't keep you awake as much.

!!! This is an addon for Chainfire3D, you need to have both Chainfire3D and Chainfire3D Pro installed to be able to use CF.lumen !!!

With the default settings, blue tints will be reduced in brightness when the sun goes down. This reduces how much looking at the screen keeps your brain awake later at night. If you have sleeping problems, you should definitely be using this. Do yourself a favor and install similar software ("f.lux") on your PC as well - it fixed my sleeping cycle.

There is also a full-on sleep mode that runs on a pre-set schedule. By default it shows the entire screen in red, so as to not destroy your night vision when you look at it.

When you want the screen to look normal for a bit (for example for gaming or looking at pictures) simply tap the notification in the notification tray to disable CF.lumen until the next time you turn on the screen.

Additionally, it can also use the light sensor to automagically switch to sleep mode when it is fully dark. HOWEVER, you should be aware that most devices do not have a sensitive enough light sensor to detect the difference between house light and darkness, so this function may not work very well on your device.

Last but not least, a function is also provided to turn off the screen based on proximity sensor activity.

Links:

Android Market (Desktop)

Thread on XDA-Developers.com