Can't adjust screen brightness on Ubuntu 12.04LTS

Try using xbacklight.

• Install it by running sudo apt-get install xbacklight in a terminal.
• Change brightness by xbacklight -set <level>, where <level> is an integer ranging from 0 to 100 (lowest brightness to highest).

For example, to set medium brightness one would use

xbacklight -set 50

Your laptop is Optimus-enabled. That means that it has two video cards: an Intel card and a Nvidia one (meant to be used for games only). This is problematic because Optimus has been designed to work with Microsoft Windows, and Ubuntu won't play very good with it.

Please check your BIOS setup, whether the Optimus option is enabled or not --if there's even any Optimus settings.

With Optimus enabled, your display will be managed by the Intel card. The brightness controls should work out-of-the-box. The Nvidia card will be fully-powered all the time though, and you need to setup Bumblebee to avoid this and to be able to use the Nvidia card for gaming.

With Optimus disabled, your display will be managed by the Nvidia card, and you'll lose the brightness controls, since the Nvidia card is not capable of accessing them.