f.lux makes your computer screen look like the room you're in, all the time. When the sun sets, it makes your computer look like your indoor lights. In the morning, it makes things look like sunlight again.

 

F.lux on Linux

 

Download the daemon https://justgetflux.com/linux.html

Then I put it into my PATH:

 /home/<user>/bin/xflux

In order to start it you have to provide your geographical location via command line.
https://justgetflux.com/map.html

If you want it to be started on boot, create a file called xflux.desktop in ~/.config/autostart (I'm using gnome maybe/probably this is different for other desktop environments, not sure though). The content of this file is:

[Desktop Entry]
Encoding=UTF-8
Version=1.0
Name=xflux
Comment=Adapts screen color temperatur according to daytime
Exec=/home/<user>//bin/xflux -l <latitude> -g <longitude>
Terminal=false
Type=Application
Name[en_US]=xflux

If you're living in the US you can also use -z <zipcode> instead of latitude and longitude.

Lisbon
38.7223, -9.1393