[adlwalrus]

There are in fact a number of free solutions...

IIRC redshift was the most developed of them when I looked into it a while back.

http://alternativeto.net/software/f46lux/?license=opensource

[dfc]

Nice! Thanks for the tip:

  dfc@ronin:~$ apt-cache search redshift 
  gtk-redshift - Adjusts the color temperature of your screen with GTK+ integration
  redshift - Adjusts the color temperature of your screen

[agumonkey]

Another thanks, the benefits are instantaneous, incredible.