How can Light sensor be enabled for control brightness and keyboard back-light automatically?

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http://askubuntu.com – i have A SONY vaio laptop F-series () Nvadia and it has light sensor when i was using windows this light sensor controlled the brightness and the keyboard backlight automatically due to the surroundings state but when using Ubuntu 12.04 it only control the backlight without automatically adjust the brightness . so the question is : how can i enable light sensor to automatically adjustment the LCD brightness* without loosing the keyboard backlight adjustment due to surrounding state ?? (HowTos)