Darker is an app that can help prevent eyestrain during the night by lowering your screen brightness to extremely low levels. It also includes a built-in color filter that can adjust the color of your display, perfect for filtering out harsh white backgrounds during the night. The app is fully functional and does not include advertisements, but additional paid features are unlockable through an In-app purchase. Xiaomi device / MIUI users need to enable "Display pop-up window" for Darker to work correctly.

Paid features include Auto-On & Auto-Off, Start at boot, Lower brightness below 20%, Darken navigation bar, Custom filter colors, Root mode, and Customizable notification buttons. The color filter is similar to how the desktop version of f.lux works. Selecting a redder color will reduce more bluelight emitted from the display. Darker also has Tasker support, which allows users to send commands to Darker using intents.

To use Darker with FlickStart, an app that can send commands to Darker using the sensors on your phone or Android Wear device, users can download the command set from the FlickStart website and import it into FlickStart.

Note that when manually installing APK files, Android blocks the "Install" button from being pressed when Darker is running. This is a protective measure to prevent malicious apps from camouflaging the install button. Pausing Darker will solve this issue.

Overall, Darker is a useful app for those who want to reduce eyestrain during the night and customize their screen brightness and color filter settings.