To fix brightness on an ASUS laptop in Ubuntu 14.04:

From askubuntu: http://askubuntu.com/questions/489247/14-04-asus-g56jr-fn-brightness-control

In the terminal:

sudo gedit /etc/default/grub

Change

GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash”

to

GRUB_CMDLINE_LINUX_DEFAULT=”quiet splash acpi_osi=”

Save, then

sudo update-grub

Restart computer.

The function keys (fn+F5/F6) should now be active.