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