The iPhone 15 uses Auto-Brightness to adjust the display according to ambient light. You can turn the feature off, but the screen will then stay closer to the brightness level you choose manually until another feature or condition changes it.
Disable Auto-Brightness
- Open Settings.
- Tap Accessibility.
- Select Display & Text Size.
- Scroll to Auto-Brightness.
- Turn the switch off.
Afterward, use Control Center or Settings > Display & Brightness to choose a manual brightness level.
Why brightness can still change
Turning off Auto-Brightness does not disable every display-management behavior. Low Power Mode, thermal protection, HDR content, attention-related features, or other current iOS behaviors can affect how bright the display appears.
If an iPhone becomes unusually warm, iOS can reduce display brightness to protect the device. Do not try to defeat thermal protection; move the phone out of direct heat, stop demanding activity, and let it cool naturally.
Leaving the screen very bright can increase battery use. If the goal is only to make the display easier to read, consider text size, bold text, contrast, or other Accessibility options instead of running maximum brightness continuously.
Matt Jacobs has been working as an IT consultant for small businesses since receiving his Master’s degree in 2003. While he still does some consulting work, his primary focus now is on creating technology support content for SupportYourTech.com.
His work can be found on many websites and focuses on topics such as Microsoft Office, Apple devices, Android devices, Photoshop, and more.