When you're working with internal and external displays, the brightness settings do not automatically match. BrightnessSync for Mac links these two settings together, but its operation is more complicated than necessary.
BrightnessSync for Mac is available as freeware, and there are no payments necessary to unlock full functioning. The program's download and installation occurred as quickly as expected. While there were no instructions in the program itself, a Readme file explained the program's operation and how to use it. Technical support was not present and it did not appear there were updates available. Upon starting, the program installs a new menu in the display preferences section of the Mac system menu. A series of sliders controls the picture for both internal and external display. A line indicating the ambient light present did not appear to work. During testing, upon clicking the internal menu, the brightness immediately went to the lowest setting and the computer had to be moved to a brighter room in order to see the screen to reset the settings. The change was also made in the native screen menu rather than the program's own window.
While basically functional, BrightnessSync for Mac would only be a useful option for people who constantly use external displays.
When you own a MacBook Pro with a Mini DisplayPort and a LED Cinema Display, you have noticed that you can control the brightness of the internal display of the MacBook Pro with the brightness keys of the keyboard. And in the Displays preferences, you can enable automatic brightness adjustment when ambient light changes for the internal display. To modify the brightness of the LED Cinema Display, you always have to use the Displays preferences, and the brightness of the external display can't be adjusted automatically.
BrightnessSync is a preference pane that eliminates this shortcoming: it enables automatic brightness adjustment for both the internal and the external display. And because the LED Cinema Display is more brilliant than the internal display of the MacBook Pro, BrightnessSync lets you set brightness levels for different ambient light conditions for the two displays independently. With this, there is nearly no need for manually adjusting the brightness for one of the both displays.
BrightnessSync was only tested with a MacBook Pro and a LED Cinema Display. It might not work with other hardware configurations, esp. with external displays that don't support software brightness control.
BrightnessSync is published unter the conditions of the GNU General Public License. The source code for BrightnessSync is included on the download image.