Like other smartphones, Android phones use an ambient light sensor to automatically adjust your phone’s display brightness. This often doesn’t work too well.

It’s up to each Android phone’s manufacturer to correctly calibrate the auto-brightness feature, and they generally don’t do an amazing job. The phone may go from too bright to too dim without anything in between.

Lux is a third-party app that allows you to easily calibrate your phone’s brightness sensor, saving you battery power and reducing eye strain if your phone is normally too bright in dark rooms.

Getting Started

We’ll be using the free Lux Lite app for this. It offers the paid version’s most important features and doesn’t even contain any advertising.

If you find the app useful, you can get the full version of Lux Auto Brightness for about $3. The full version allows you to set your screen brightness to very low levels — good at night — and offers modes that tint your screen different colors, similar to how f.lux works on Windows.

To get started, open the Lux Dash app after installing Lux.

Creating Linked Samples

To train Lux, you’ll have to create “linked samples.” Whenever you feel that your phone’s display brightness level isn’t ideal for the current level of ambient light in the room — whether it’s too bright or too dark – you can create a linked sample. This means that you’ll adjust the brightness level manually, then tell Lux that this brightness level is ideal for the current level of ambient light. Create several of these linked samples and Lux will learn what the appropriate levels of brightness for different situations are.

This works much better than automatic brightness does on stock Android. If you’re not happy with your automatic brightness level, you have to disable automatic brightness entirely and adjust the brightness level manually. If you use Lux, you can adjust the brightness level manually and teach Lux to do a better job in the future. Android’s default automatic brightness feature can’t learn in this way.

The two values at the top of the Lux dash are screen brightness level, measured as a percentage, and ambient brightness level, reported by the ambient brightness sensor as an lx value. To create a linked sample, just adjust the brightness slider in the Lux app and tap the link button.

The ambient brightness and screen brightness levels will be linked after you confirm the values.

If you make a mistake and aren’t happy with how you’ve trained Lux, you can also view your linked samples and delete any of them or reset Lux to its default settings.

Setting Your Adjustment Type

By default, Lux is set to only change your phone’s brightness level on wake. When you take your phone out of your pocket and wake it up, Lux will take a measurement of the ambient brightness level from your phone’s ambient light sensor and set the appropriate brightness level. It won’t continue to adjust the screen’s brightness level as you use your phone.

On the one hand, this can be useful. You won’t be distracted by your phone’s screen brightness changing as you use it. On phones with bad brightness sensors, the screen brightness may normally fluctuate as you use it,  distracting you — not so with this setting. On the other hand, if you go from a bright location to a dark location, or vice versa, your phone won’t automatically adjust its display brightness.

To tweak this behavior, you can choose one of several different adjustment types:

  • Manually: This mode disables automatic brightness entirely, allowing you to adjust your screen’s brightness manually.
  • On Wake: Lux changes your screen’s brightness when you wake up your phone. This is the default setting.
  • Dynamically: Dynamic mode adjusts your screen’s backlight brightness whenever a “significant change” in ambient brightness occurs. There’s some delay to prevent the brightness level from fluctuating wildly, and these delays are customizable in Lux’s settings.
  • Periodically: Lux periodically checks the ambient brightness level and then adjusts your screen’s brightness. Lux does this every five seconds by default, but you can customize the time period.
  • Ascendingly: Lux will increase your phone’s screen brightness when the ambient brightness level increases, but won’t decrease it when the ambient brightness level decreases. The brightness level will be reset when your phone goes to sleep. This is particularly useful for phones with inaccurate brightness sensors that swing back and forth or rooms with constantly changing brightness levels.

On Wake works well if you regularly take your phone out of your pocket to use for short bursts, as your phone will choose an appropriate screen brightness level each time. if you’re using your phone for longer periods and want the screen’s brightness level to adjust automatically, the Dynamically setting will be your best bet — although if light levels continue to change or your phone’s brightness sensor is unreliable, you’ll want to try the Ascendingly setting.

To use Lux, all you really need to do is keep creating linked samples to train its automatic brightness algorithm for your phone and your personal preferences. You should also choose the adjustment type that works best for you. Other options are available, but these are the most important ones.

Profile Photo for Chris Hoffman Chris Hoffman
Chris Hoffman is Editor-in-Chief of How-To Geek. He's written about technology for over a decade and was a PCWorld columnist for two years. Chris has written for The New York Times and Reader's Digest, been interviewed as a technology expert on TV stations like Miami's NBC 6, and had his work covered by news outlets like the BBC. Since 2011, Chris has written over 2,000 articles that have been read more than one billion times---and that's just here at How-To Geek.
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