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yacine04
User level: Level 1 (4 points)

MacBook Air M4: screen brightness increases by itself since macOS 27

Since updating to macOS 27, the screen brightness on my MacBook Air M4 increases on its own, without any input from me.

  • Model: MacBook Air M4
  • macOS version: 27.0
  • No external display connected (built-in display only)
  • Frequency: intermittent, not sure how often it happens

Users on Tahoe 26.4 have described similar behavior, even with automatic brightness turned off.

Is anyone else seeing this on macOS 27, or has anyone found a fix?

Posted on Sep 19, 2026 2:11 AM

1 reply

Owl-53
User level: Level 10 (123,805 points)

Sep 19, 2026 5:44 AM in response to yacine04

If the brightness on your MacBook Air M4 increases without user input, first go to System Settings >> Displays and make sure Automatically adjust brightness is turned off. 


Apple documents this as the setting that automatically adjusts display brightness. (Apple Support)


As a diagnostic step, temporarily turn True Tone off. Apple states that True Tone uses ambient-light sensors to adjust the display's colour and intensity. (Apple Support)


Next, install any available macOS 27 update under System Settings >> General >> Software Update. 


Keeping macOS updated is one of Apple's recommended troubleshooting steps for software-related problems. (Apple Support)


If the brightness still changes with Automatically adjust brightness and True Tone disabled, note exactly when it occurs, for example, after waking from sleep, while connected to power, or while using a particular application. 


This can help establish whether the behaviour is reproducible under specific conditions.


If it continues, test the Mac in Safe Mode. 


On an Apple-silicon Mac, shut down, press and hold the power button until Loading startup options appears, select the startup volume, hold Shift, then click Continue in Safe Mode. 


Use the Mac in Safe Mode long enough to determine whether the brightness changes again. Apple provides the startup instructions here: Mac startup options.


If the problem also occurs in Safe Mode, Apple Diagnostics can be used to check for a possible hardware issue. 


On an Apple-silicon Mac, shut down, press and hold the power button until the startup options appear, then press and hold Command-D. (Apple Support)


At that point, if Diagnostics reports no hardware problem but the brightness continues to change unexpectedly, the documented troubleshooting does not establish a specific cause. The circumstances and frequency of the brightness changes should then be provided to Apple Support for further investigation.

Originally posted at discussions.apple.com/thread/256360339