If the brightness controls don’t works in your system or you’re not satisfied with the default Fn function key, here’s an app indicator allows to change screen brightness in all the possible brightness values. The applet works in Ubuntu and its derivatives, such as Linux Mint and Elementary OS Luna.
It’s useful for me because the Fn+Arrow key in my laptop only change the brightness in 4 levels (zero, one third, two-thirds, full).
Install Brightness Indicator:
Press Ctrl+Alt+T on your keyboard to open terminal. When it opens, run below commands one by one to install the indicator from PPA:
sudo add-apt-repository ppa:indicator-brightness/ppa sudo apt-get update sudo apt-get install indicator-brightness
Or you can download the .deb package and double-click to install it from Launchpad.net
Once installed, open it from the app menu. Add these commands to your custom keyboard shortcuts to control brightness with your keyboard. You need Elementary Tweak to add a custom shortcut key.