The brightness of old Apple Cinema Displays can no longer be controlled in the modern versions of macOS.
This little tool lives in the menu bar and can control the following Apple Cinema Displays connected by USB to the machine:
Apple Cinema Display 20", 23" & 24"
Apple LED Cinema Display 24"& 27"
Apple Cinema HD Display 30"
The tool is provided for free as is. You use it completely at your own risk! I do not guarantee anything.
VERSION HISTORY
Version 1.1 published on 17 November 2025
support for reading and decoding EDID information
Version 1.0 published on 15 November 2025
initial version with support for multiple Cinema Displays