Redshift

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.

Run redshift -h' for help on command line options. You can run the program as redshift-gtk' instead of 'redshift' for a graphical status icon.

Website: http://jonls.dk/redshift/
Project page: http://launchpad.net/redshift