Brightness control doesnt work in Live Ubuntu 12.10 in Sony Vaio VPCCW15FN/R

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http://askubuntu.com – I am using Sony Vaio VPCCW15FN/R model..I am running Live Ubuntu 12.10 using USB.The problem I am facing is that after booting, in Ubuntu i am unable control brightness.I can control volume using Fn key shortcut but not brightness..i got to know that its Nvidia Graphics card issue..Due to extreme brightness, I am getting lots of stretch on my eyes..Please help ASAP..Thanks in advance.! (HowTos)