I was using ubuntu 10.10 for long time, there also I had a brightness control problem in my laptop. By editing /etc/X11/xorg.conf it's fixed. Now I upgraded to 13.04, on this even after adding enable brightness in xorg, brightness control is not working. From other posts, I tried all combinations in /etc/default/grub, update grub and restart. None of the combination are working. My laptop model is lg r480, having nvidia g105M graphics card. Can anyone please give me a solution for this.