Shades is a FREE utility for controlling the brightness of your screen. It runs in the background providing always-available fine-grained control over the brightness of your display via a slick Mac-like interface
via Shades | Software | Charcoal Design.
My new Thunderbolt Apple Display seemed to be rather dark, compared to other displays and what I expected. Thanks to the Shades app I then found out that the display had a factory brightness setting of only about 50% of its maximum brightness. Shades now lets me control the Apple Display’s brightness.