How iPhone Auto-Brightness Works

By Mary Jo Megginson

The auto-brightness feature on your iPhone can conserve battery power and reduce eye strain.
i Andrew H. Walker/Getty Images Entertainment/Getty Images

Many smartphones come with an auto-brightness feature that aims to both conserve battery power and make the screen easier to see when you are using it. The iPhone's auto-brightness feature has been on every model since the smartphone was introduced by Apple in 2007. Although at least one study has questioned the effectiveness of the auto-brightness feature, it can still help to reduce eye strain and conserve battery power if enabled.

iPhone Screen Specifications

The glass touch-screen LCD display of the iPhone measures 3.5 inches diagonally. It has a resolution of 480 by 320 pixels at 163 ppi (pixels per inch).

Turning Auto-Brightness On

Turn on your iPhone and tap "Settings" on your Home screen. Tap "Brightness" to open the display brightness settings. Slide the "Auto-Brightness" slider until "On" appears. Press the "Home" button to return to the Home Screen.

How It Works

The iPhone uses a sensor to detect ambient light in your environment. It dims the screen in a dark environment and brightens it when you are in an area with ample ambient light. The brighter screen helps to counteract the washed-out nature of screen images caused by glare and takes into account the decreased sensitivity of your eyes to brightness as light levels increase.


Your iPhone's display is a heavy battery consumer. When auto-brightness works properly, it ensures that you are never using more battery power than you need by adjusting the screen brightness to your environment. With extended battery life, you will be able to use your iPhone for longer periods of time before you have to charge it.

How to Test Auto-Brightness

Remove your iPhone from its case (if you have one) and peel off any protective film. From the Home screen, tap "Settings" and then "Brightness" to ensure that Auto-Brightness is set to "On." Press the "Home" button and then lock your iPhone by pressing the "Sleep/Wake" button. Move into an area with bright ambient light and use your hand to cover the top third of your iPhone screen. Press the "Home" button and move the slider to unlock your phone. The screen should appear dimmed. Remove your hand from the top third of the display. If auto-brightness is working properly, your screen will get brighter.