「Night Screen」is a Material Design Application which can protect your eyes from being hurt by screen, creating a mask at the top of screen in order to make screen darker. We can solve the problem that the lowest brightness is not low enough in some devices.
(PS: Even though you are using our application to make screen darker, you should reduce the time watching screen in a dark environment.)

( Enable permission in Android 6.0: "Settings" app - "Apps" - The gear icon - "Draw over other apps" - "Night Screen" - Then enable it )

Otherwise, this application is open source under GNU GPL v3 License.
Github Repo: https://github.com/fython/Blackbulb