Comment 19 for bug 762670

I can also confirm that the suggestion posted by "Pierre Chifflier" works. Though myself not being a computer geek I had problems implementing it. Below is the example of how it looks on my xorg.conf file and this works for me.

Section "Screen"
    Identifier "Screen0"
    Device "Device0"
    Monitor "Monitor0"
    DefaultDepth 24
    Option "TwinView" "1"
    Option "TwinViewXineramaInfoOrder" "DFP-2"
    Option "metamodes" "DFP-0: 1680x1050 +1920+15, DFP-2: 1920x1080 +0+0"
    Option "RegistryDwords" "EnableBrightnessControl=1"
    SubSection "Display"
        Depth 24
    EndSubSection
EndSection

Note: this is just an example for those who don't know where the following line appears

Look above for => Option "RegistryDwords" "EnableBrightnessControl=1"

Thanks everyone, Special Thanks to "Pierre Chifflier"

Cheers,
Hemant