Easily select the existing brightness level or set it manually. All easily and from your Android home screen
This is widget, which allows you easily change screen brightness.
RE ADD WIDGET AFTER UPDATE!!!
If you have problems with ad window int ICS - it's a bug in Launcher/Play/Market:
1. remove auto created shortcut from desktop
2. launch the BrightnessLevel from apps list
3. if you still can see ad window, press back until you get to desktop
4. try to run BrightnessLevel from apps list again, it should disappear.