A few weeks ago, the makers of the popular desktop screen filter f.lux started testing an Android version in private beta. Now, the app is live in the Play Store for everyone. You will need to be rooted, but the app is completely free.

The premise of apps like this is that blue light can interfere with your sleep cycle, so it's best to filter it out in the evening. There are a few Android apps that do that like CF.lumen and Twilight, although the latter uses a non-root red overlay that may or may not work as well as the root methods. f.lux includes scheduling, various color temperature features, and more.

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The developers say the app should work on most rooted Marshmallow and Lollipop devices, as well as some earlier builds of Android on certain devices. The developers originally said you'd have to sign up for this beta, but it appears to be available to everyone without signing up. Maybe they're just throwing caution to the wind now that Android N is adding a more robust night mode.

f.lux (preview, root-only)
f.lux (preview, root-only)
Developer: justgetflux
Price: Free