How to Turn Off Auto-Brightness on iPhone

Auto-Brightness adjusts the screen to match the light around you. If the screen keeps dimming when you do not want it to, the switch is buried in Accessibility, not in Display & Brightness.

Open Accessibility settings

Open Settings and tap Accessibility.

Tap Display & Text Size

Under the Vision section near the top, tap Display & Text Size.

Scroll to the bottom and turn off Auto-Brightness

Scroll all the way down. Auto-Brightness is the last toggle on the screen. Turn it off. The screen stays at its current brightness and will no longer change on its own when you walk outside or into a dark room.

Set the brightness yourself

Open Control Center by swiping down from the top-right corner (or up from the bottom edge on an iPhone with a Home button) and drag the brightness slider, the tall one with the sun icon, to the level you want. You can also drag the slider under Settings, Display & Brightness. Whatever you set now stays put until you change it again.

If you are looking under Display & Brightness. That screen has the manual brightness slider, True Tone, and Night Shift, but the Auto-Brightness toggle has lived under Accessibility since iOS 11. Nothing is missing from your phone, and True Tone is a separate feature that adjusts color, not brightness.

If battery life gets worse. With Auto-Brightness off, the screen stays as bright as you set it even in a dark room, which uses more power and, according to Apple, can affect long-term display performance. Lower the slider when you can, or turn Auto-Brightness back on and adjust the slider, which sets the baseline it works from.