A free app for Android, by justgetflux.

The purpose of f.lux is to give you a preview of what to expect when you install it. We plan to release a final version of f.lux that works on all devices. This version requires root and a special build of Lollipop or Marshmallow. You will not need to do anything special to use this version.

This currently has two main issues. One is it does not work on a lot of Samsung Galaxy devices. Another is that your device’s screen will flash anytime an app is updated through Google Play.