I have prepared a python script which you can use to control brightness of your laptop. Download brightness.py and save the file some where on your system.
Install xbindkeys to map keyboard shortcuts.
sudo apt-get -y install xbindkeys
Execute following command to initialize your xbindkeys configuration file.
xbindkeys --defaults > ~/.xbindkeysrc
Now copy and paste following snippet at the end of your .xbindkeysrc file.
"python [script path]/brightness.py down" m:0x5 + c:100 Control+Shift + Left "python [script path]/brightness.py up" m:0x5 + c:102 Control+Shift + Right
Make sure you replace [script path] with the path of the folder that contains downloaded python script. Open up your terminal and execute following command to start xbindkeys.
Now test your shortcut keys Control+Shift+Left Arrow and Control+Shift+Right Arrow. Make sure you add xbindkeys command to ubuntu sessions so that xbindkeys is automatically started every time you login.
Enjoy ubuntu :)