Well my friends have been facing brightness problem in Ubuntu 12.04 Precise Pangolin. And every one were facing and asking me to help me out with it. So, I viewed all over the Internet and helped them out. I helped with it myself too in Dell XPS 13. And for friends Acer Aspire, HP Pavilion DV6. So it might work on most of all the PCs.
My friends were just trying the xrand solution that just decreases the Contrast which had no effect on the power consumption. So, this solution was the most to be kept. I am feeling quite when the Fn(Function key) and the Brightness Up and Down are working great. You can follow up the procedure that I have kept in an easy steps.
Open terminal ( Ctrl+Alt+T ) and type:
sudo gedit /etc/default/grub
You will find this line in the new opened window:
1 GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
Change it to:
1 GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi_backlight=vendor"
Save and close the window and type this in the terminal:
This will update your grub and while rebooting your PC, it will set an extra parameter on the grub menu during boot. This problem might have occur on due to the upgrade on kernel.
Enjoy the power saving system.