Why does my MacBook's screen continually dim and brighten without my input?

Solution 1:

Go your System Preferences, select "Displays", and uncheck Auto-adjust Brightness.

Solution 2:

Might be an issue with the power supply when “Slightly dim the display when on battery power” is checked in Energy Saver prefs. This would dim the display when the power adapter is lost and become brighter again when not running on battery anymore.

Solution 3:

The "Auto-adjust Brightness" didn't fix it for me, but disabling the option right under it, "True Tone", did.

Solution 4:

This could be a keyboard issue. If other things are going wrong with keys, such as the backspace or caps lock, the keyboard (top case) needs replacing.

You can get a temporary fix by using a keyboard remapper program and change the keys for brightness and turn off the usual F1 and F2 ones.

Solution 5:

I'd try to reset the System Management Controller (SMC).

Apple's documentation on the SMC states that this may resolve issues related to the power management. The document specifically mentions:

The display backlight doesn't respond correctly to ambient light changes on Mac computers that have this feature.

As the guidelines on how to reset the SMC depend on your kind of Mac, I will not list them all here. Please follow the link and go to the section with the title Resetting the System Management Controller (SMC) for more information on how to apply the reset.

Should that not work, you're left with two other avenues to remedy this:

• software errors - you might need to troubleshoot or restore the OS
• hardware fault - the display and sensor might simply need repair