The website states:
"Redshift adjusts the color temperature of your screen according to your surroundings. This may help your eyes hurt less if you are working in front of the screen at night. This program is inspired by f.lux [...]."
The project is developed on launchpad.
Redshift will at least need your location to start, meaning the latitude and longitude of your location. Redshift employs several routines for obtaining your location. If none of them works (e.g. none of the used helper programs is installed), you need to enter your location manually: For most places/cities an easy way is to look up the wikipedia page of that place and get the location from there (search the page for "coordinates").
To just get it up and running with a basic setup, issue:
$ redshift -l LAT:LON
where LAT is the latitude and LON is the longitude of your location.
Redshift reads the configuration file
~/.config/redshift.conf, if it exists. However, Redshift does not create that configuration file, so you have to create it manually.
Example for Hamburg/Germany:
; Global settings [redshift] temp-day = 5700 temp-night = 3500 transition = 1 gamma = 0.8:0.7:0.8 location-provider = manual adjustment-method = vidmode ; The location provider and adjustment method settings ; are in their own sections. [manual] ; Hmaburg lat = 53.3 lon = 10.0 ; In this example screen 1 is adjusted by vidmode. Note ; that the numbering starts from 0, so this is actually ; the second screen. [vidmode] screen = 0 screen = 1
After you created that file, start redshift from the menu of your DE (called "gtk-redshift") or type the following in your terminal:
$ gtk-redshift &
Using "gtk-redshift" instead of "redshift" launches Redshift with a system tray icon for easier handling of the application. Finally, if you want to start Redshift automatically on system startup, rightclick the system tray icon an check "Autostart".
If -- for some reason --will not get installed automatically as dependency and Redshift refuses to start, check if python2-xdg is installed:
$ pacman -Qi python2-xdg
If it is missing, install it as dependency:
# pacman --asdeps -S python2-xdg