Wow… one more reason to love GNU/Linux…
Today I came to know about one more utility… xbacklight
xbacklight can be used to adjust screen brightness.
e.g. : $ xbacklight -set 50%
This will set screen brightness to 50%
Try $ xbacklight -help for more information.
Useful utility for laptop users. You can even set the Login Screen
brightness. Just find config file of your Display Manager (KDM, GDM, XDM)
and change it accordingly.