Fix Brightness control Issues in ubuntu 12.04 or 14.04.

The brightness control was not working and after trying several solutions, the one that worked for me was

Find if your computer is using onboard graphics card (On motherboard) or the discrete graphics card (Nvidia or ati radeon etc).

sudo cat /sys/kernel/debug/vgaswitcheroo/switch

On my computer I get the following.

Here IGD means Integrated graphics card which is Intel in my case.[See your computer specfication for this info].

And DIS means Discrete graphics card which is ATI in my case.s

Look for the '+' sign.
Since IGD has the plus sign that means that my computer is using the onboard graphics Intel card.

Now if your computer is INTEL too, then follow the below steps.

Create the file if it is not there.

sudo touch /usr/share/X11/xorg.conf.d/20-intel.conf

sudo gedit /usr/share/X11/xorg.conf.d/20-intel.conf
Add the below text into the file and save it.
Section "Device"
        Identifier  "card0"
        Driver      "intel"
        Option      "Backlight"  "intel_backlight"
        BusID       "PCI:0:2:0"EndSection


Save it and log out and log back in. Now your brightness will start working.