Night light is an open-source app which uses KCAL to adjust blue light intensity of the display colors so that viewing the screen at dark becomes pleasant for the eyes and help you fall asleep faster (this is what science have proven so...).

Source - https://github.com/corphish/NightLight

Features
- Easy to use user interface. Settings are easier to find.
- Uses KCAL to adjust screen RGB colors hence its efficient and changes are seen everywhere on screen.
- Supports older KCAL implementations as well as newer KCAL implementation for v4.4 kernels.
- Simple color controls for normal users through color temperature control.
- Manual KCAL controls for advanced users.
- Maximum and minimum color intensities. Use minimum intensity at evenings under lighted conditions and maximum intensity at nights under pitch dark conditions.
- Support for user profiles which are collections of settings that user can apply with one click.
- Automatic switching on/off night light at user specified timings.
- Supports sunset/sunrise timings.
- Additionally dark hours start time is supported to make use of minimum and maximum intensities.
- And to fulfill your all kinds of automation needs app is supported as a Tasker plugin. You can use it with Profiles.
- Set on boot delay.
- Original KCAL settings of user is backed up and applied when night light is turned off. And it can be configured as well.
- Quick Setting tile for easy toggling on/off night light anywhere.
- Launcher icon shortcut for toggling Night Light on/off and toggling intensities.
- Dark and Light theme.

Requirements
- Kernel supporting KCAL.
- Root access.

Permissions required
- Location - It is used to determine sunset/sunrise times for your location. (Your location info isn't shared your privacy is maintained)
- Internet - It is used to determine approximate location (when exact location is not available) to determine sunset/sunrise times for your location.