I have a Dell Studio 1558. When I originally installed 13.04 on it, I had to modify my
/etc/default/grub with the following:
GRUB_CMDLINE_LINUX_DEFAULT="acpi_backlight=vendor dell_laptop.backlight=0 quiet splash"
Doing that made everything work, the keyboard brightness buttons, the OSD in the top right corner, and the brightness slider in System Settings. However, upon upgrading to 13.10, I once again am unable to adjust the backlight. This is also the case if I use either of the following:
GRUB_CMDLINE_LINUX_DEFAULT="acpi_backlight=vendor quiet splash"
The backlight is stuck at a single brightness level, at a guess I think it's somewhere around 50%. The OSD still comes up if I push the keyboard buttons, but the bar only goes down one division from 100% and resets back to 100%, if I press decrease again. The slider in 'System Settings' does nothing.
Any help is greatly appreciated!