Archived note: this post was published in 2010. Commands, screenshots, and third-party integrations may no longer match current tools.

If you want to change the screen brightness in Ubuntu (I can’t change it using the keyboard shortcuts or the Ubuntu Power Management menu), open a terminal and execute the following:

sudo setpci -s 00:02.0 F4.B=xx

Where xx is the desired brightness in hex ranging from 0 (brightest) to FF (no brightness at all). I usually change it to CA when working on battery.

Cheers!