brightness laptop

Ubuntu 14.04, xfce (xfce4),

create the file
 /usr/share/X11/xorg.conf.d/20-intel.conf

with content

Section "Device"
        Identifier  "card0"
        Driver      "intel"
        Option      "Backlight"  "intel_backlight"
        BusID       "PCI:0:2:0"

EndSection

source:http://itsfoss.com/fix-brightness-ubuntu-1310/