Apparently, there’s a macOS bug that if your Mac has been connected to a Thunderbolt Display for a long time, the brightness of the display can no longer be adjusted (neither by pressing the according F1/F2 keys on your keyboard nor by using the brightness slider in the display settings of the system preferences).
The simple yet surprising fix is:
- Unplug your Thunderbolt Display’s Thunderbolt cable, and plug it in again
- The display’s brightness will be adjustable again
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.