A simple application that works on both Windows and Linux to change the system backlight level.
Ubuntu will need the package libmono-system-management4.0-cil, since System.Management is used for the Windows Portion.
Once built (open in Visual Studio or MonoDevelop and hit Build) you can run it by:
(Linux)
sudo mono IBC.exe 10 (Sets backlight to 10% of max)
(Windows)
IBC.exe 10 (Same effect, but Windows doesn't require root.)
Valid Values are 1 to 100.
I shouldn't have to mention this, but I will anyway: This obviously requires you to have a screen whos brightness can be controlled by software - IE most Laptops, and almost never Desktops.