Darkness

Keep brightness levels consistent between built-in and external displays

How to use this app

1. Clone and build, or download a pre-built copy and unzip it.
2. Open the Privacy tab of the Security & Privacy pane of System Preferences, and drag Darkness to the list of apps in Input Monitoring and/or Accessibility (this varies depending on the version of macOS).
3. Run Darkness. You should see all displays dim slightly, which indicates it's working.
4. Set the brightness level of all displays attached to your Mac to the maximum level each is capable of.
5. Unless all displays have the same maximum brightness level, reduce the brightness of the brighter displays to that of the dimmest display. The idea is to have all displays at the same level of brightness, and for that level of brightness to be only as bright as the dimmest display is capable of, because this app can only make displays appear darker.
6. Use the F1 and F2 keys (i.e. the brightness keys with the fn key held down) to adjust the apparent brightness of all attached displays consistently.

By default, this app has no visible user interface. To quit it, you can activate the app by re-opening it from the Finder, and then press command-q. Alternatively, you can use the shell by doing e.g. pkill Darkness. To enable a Dock icon and menu bar with a Quit item, change the value of the LSUIElement key in Info.plist to false.