Brightness doesn't change on Sony laptop

I installed ubuntu 12.04 on my laptop for first time and every thing work well but the only thing doesn't work is the brightness doesn't change when I press F5 and F6 with Fn

So I can't adjust the Brightness and sometimes I need to decrease it for more time working on battery

and the bubble appear that it changed but nothing happens

My laptop is Sony VAIO series F with NVIDIA GEFORCE ...

and NVADIA accelerated graphic driver is activated

Solution 1:

LCD Brightness Control

Once you have installed the proprietary Nvidia drivers as suggested above, you may notice that your brightness control keys do not work properly. This is fixable by editing one's xorg.conf file. Open a terminal window and type the following:

sudo nano /etc/X11/xorg.conf

This will open your X server configuration (after prompting for your password). You should see a section titled "Device" that looks as follows:

Section "Device"
        Identifier      "Default Device"
        Driver  "nvidia"
        Option  "NoLogo"        "True"
EndSection

Append a line so it appears like this:

Section "Device"
        Identifier      "Default Device"
        Driver  "nvidia"
        Option  "NoLogo"        "True"
        Option "RegistryDwords" "EnableBrightnessControl=1"
EndSection

You will need to restart your graphical server (or reboot) for this change to take effect.