Here's how you can enable the brightness applet on your Cinnamon desktop in Linux Mint 14 or 13.
1. Click the caret icon on the bottom panel.
2. Choose Settings.
3. Choose Applets.
4. On the applets menu, click the box next to Brightness to enable the applet.
You can now easily adjust screen brightness on your Linux Mint desktop.
For more, see the original article at the link below.