Screen randomly dims or brightens on its own — not a bug, it's a feature
You're in a meeting and your screen suddenly dims. Or you turn on a lamp and the brightness jumps. The keyboard backlight does the same thing. First instinct is that something's wrong with the hardware, but nope — Mac is just doing it on purpose.
Why does this happen?
MacBooks have a built-in ambient light sensor that automatically adjusts display brightness and keyboard backlight based on the lighting in your environment. The intent is to save battery and reduce eye strain, but the sudden changes can feel totally random.
How to fix it
To disable auto-brightness: System Settings → Displays → uncheck Automatically adjust brightness.
To disable keyboard backlight auto-adjustment: System Settings → Keyboard → uncheck Adjust keyboard brightness in low light.
You can keep one enabled and disable the other independently.
Discussion
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