nixos-conf/services/redshift.nix

{ config, ... }:
{
  assertions = [
    {
      assertion = config.services.xserver.enable;
      message = "Redshift does not work without a desktop!";
    }
  ];
  services.redshift = {
    executable = "/bin/redshift-gtk";
    enable = true;
    temperature = {
      night = 2800;
      day = 6500;
    };
    brightness = {
      night = "0.5";
      day = "1";
    };
  };

  location = {
    latitude = 60.17;
    longitude = 24.94;
  };
}