Awesome

Lumen

Lumen is a menu bar application for macOS that magically sets the screen brightness based on your screen contents.

You control Lumen simply by using your brightness keys - it'll automatically learn your preferences.

Lumen will automatically brighten the screen when you're looking at a dark window (for example, a full-screen terminal) and it'll automatically darken the screen when you're looking at a bright window (for example, a web browser). This makes for a much more pleasant experience, especially at night.

Demo

Without Lumen, web pages are too bright, and the terminal is too dark to read. With Lumen, it's perfect.

Download

The easiest way to install Lumen is to use Homebrew Cask:

brew install --cask --no-quarantine lumen

On macOS 11, you will need to grant screen recording permission to Lumen (it grabs the screen to see whether dark or light content is being displayed). You can grant the permission when it's first requested, or you can go to System Preferences > Security & Privacy > Privacy > Screen Recording and check the box next to Lumen.

If you prefer, you can manually install the binary. You can find pre-built binaries here.

As of now, releases are not signed with a developer key. To open unsigned applications for the first time, use this method.

Notes

Lumen isn't supposed to work with auto brightness enabled, so be sure to disable the "automatically adjust brightness as ambient light changes" feature in System Preferences. Lumen also isn't compatible with f.lux or Night Shift, so it may not work properly while you are using those.
Lumen does not natively support external monitors. If you want to control the brightness of an external monitor with Lumen, you can use Lunar to sync your external monitor's brightness with your laptop screen.

Contributing

Feature requests, bug reports, and pull requests are all appreciated.

Related Projects

bencevans/lumenaire - a cross platform implementation of Lumen written in Node.js
epilande/lux - a cross platform implementation of Lumen written in Node.js
meh/dux - a Linux implementation of Lumen (with some extra features) written in Rust
maximbaz/wluma - a Linux implementation of Lumen (with some extra features) written in C
autolume/autolux - a Linux implementation of Lumen written in Python
AlaaAlShammaa/Luminance - a Windows implementation of Lumen written in Java

Note: I haven't personally audited the code from these projects.