Comment 25 for bug 537763

@SKid: these parameters go in /etc/default/grub. Simply do:

- Press Alt+F2, enter "gksudo gedit /etc/default/grub" and press enter
- Change the line that reads
    GRUB_CMDLINE_LINUX=""
  to
    GRUB_CMDLINE_LINUX="acpi_osi=Linux acpi_backlight=vendor"
- Save and exit
- Press Alt+F2, enter "gksudo update-grub", tick "Run in terminal" (to see
  the progress) and press enter

Notice the "acpi_backlight=vendor" bit. This is a suggestion from another user in a duplicate-ish of this bug (dealing with the same problem for a different eeepc model), which makes the brightness OSD and automatic brightness adjustment features work correctly.