Brightness Problem in Ubuntu 12.10

description: brightness hot key does not work & can't change brightness in the setting: screen brightness is always at max eating up battery...

Below is how to solve this problem by editing "grub"

1. Run this command:
   

   gksu gedit /etc/default/grub
   

2. Change the line GRUB_CMDLINE_LINUX="" into GRUB_CMDLINE_LINUX="acpi_osi=Linux".
   Save the file and quit the text editor.
3. Then run: sudo update-grub
4. Restart.