Try this: 1. Start Lumen 2. Open up a dark window (e.g. a terminal) and make your display bright according to your preferences 3. Wait a second 4. Open up a li

Try this: 1. Start Lumen 2. Open up a dark window (e.g. a terminal) and make your display bright according to your preferences 3. Wait a second 4. Open up a light window (e.g. a web browser) and make your display darker according to your preferences 5. Wait a second Now try switching back and forth between the two, and you should see it automatically doing stuff.