Stop your MacBook screen dimming when you unplug it

Why it happens

Mac laptops save power by lowering the brightness a little as soon as they run on battery. That's the Slightly dim the display on battery setting, and it's on by default. Low Power Mode can also dim the screen to make the battery last longer.

How to fix it

1. Open the Apple menu, choose System Settings and click Battery in the sidebar.

2. Click Options… near the bottom of the Battery page and turn off Slightly dim the display on battery. Click Done.

   Battery›Options…›Slightly dim the display on battery

3. Back on the Battery page, look at Low Power Mode. Set it to Never if you want full brightness on battery. Some Macs show Energy Mode instead: there, choose Automatic for On battery.

   Battery›Low Power Mode

4. Unplug the charger to test. The screen should stay at the same brightness.

Still not fixed?

1. If the brightness drifts up and down with the light in the room, that's the light sensor. Turn off Automatically adjust brightness in Displays settings if you'd rather set it yourself.

   Displays›Automatically adjust brightness

2. If the screen dims after a minute or two of not touching anything, that's the step before the display turns off. Choose a longer time for Turn display off on battery when inactive in Lock Screen settings.

   Lock Screen

3. To bring the level back up, press the brightness up key (F2, with a sun on it) on the top row. On a MacBook Pro with a Touch Bar, tap the brightness button at the right of the Touch Bar.

4. If the screen dims, flickers or goes dark on its own even while plugged in, the display or its backlight may be faulty. Contact Apple Support or an Apple Authorized Service Provider to have it checked.