The laptop brighness control is not software driven it is hardware driven. The desktop LCD also has a brightness control, and it is also hardware driven. It is a button on the monitor itself.
You can adjust brightness with certain graphics controllers, example, ATI's Control Center will adjust brightness in the menu called Color Control. You can do that from the keyboard following the menu commands. There is no indicated direct key command or macro for that.
The quickest and easiest way is to use the monitor's control buttons.