On my Acer Aspire with Ubuntu 14.04, using function key to change the brighness did not yield any results. Brighness can not change. My laptop uses cards: Nvidia Graphics and Intel graphics.
FIND VIDEO/GRAPHICS CARD IN UBUNTU
Run the command below in terminal to know what video card is used for the backlight/brightness:
As you can see, the output for me is intel_backlight. An indicator that the graphics card in use is Intel.
If your graphics card is Intel, you can proceed with the fix below:
FIX BRIGHNESS CONTROL ISSUE WITH INTEL CARD IN UBUNTU 14.04
Open a terminal and create the following configuration file, if it does not exist:
sudo touch /usr/share/X11/xorg.conf.d/20-intel.conf
Now we need to edit this file. You can use any editor be it a terminal one or graphical.
sudo gedit /usr/share/X11/xorg.conf.d/20-intel.conf
Add the following lines to this file:
Section "Device" Identifier "card0" Driver "intel" Option "Backlight" "intel_backlight" BusID "PCI:0:2:0" EndSection
Save it. Log out and log in back. The brightness control should be working through function keys now.
Original post: http://itsfoss.com/fix-brightness-ubuntu-1310/