Taking Manual Control of Your Screen Lighting
By default, Apple enables a feature called “Automatically adjust brightness” on every single MacBook and iMac. This system relies on a tiny ambient light sensor hidden in the top bezel of the screen (right next to the webcam). As the lighting in your physical room changes throughout the day, the sensor detects it and automatically dims or brightens your Mac’s screen to compensate.
In theory, this is designed to save battery life and reduce eye strain in dark rooms. In reality, it can be incredibly frustrating. If you are sitting near a window on a cloudy day, the screen might constantly flicker brighter and darker every few minutes as the sun moves behind the clouds. Furthermore, if you are a photographer or graphic designer editing images, you need your screen brightness to remain completely consistent to accurately judge colours.
If you prefer to manually control your screen brightness using the keys on your keyboard, you must disable the automated sensor.
How to Disable Auto-Brightness in macOS
Apple places this setting inside the main Displays menu, though it is slightly less prominent on modern versions of macOS than it used to be.
- Click the Apple Logo in the extreme top left corner of your screen.
- Select System Settings from the dropdown menu (if you are using an older Mac, this will be called System Preferences).
- In the left-hand sidebar, scroll down and click on Displays.
- Look closely at the settings available for your built-in display. You will see a slider allowing you to manually adjust the brightness.
- Directly beneath that slider, look for a toggle switch labelled Automatically adjust brightness.
- Click the toggle switch to turn it to the Off position (the switch will turn from green to grey).
Your Mac will instantly stop listening to the ambient light sensor. From now on, the screen brightness will only change when you explicitly press the F1 (dim) or F2 (brighten) keys on your keyboard.
What About “True Tone”?
While you are in the Displays menu, you will likely notice a second, closely related setting located right next to the auto-brightness toggle called True Tone.
While auto-brightness changes how bright the screen is, True Tone changes the colour temperature of the screen. It uses the exact same sensor to detect whether the light in your room is cool (like fluorescent office lighting) or warm (like a yellow bedside lamp). True Tone then subtly shifts the white balance of your Mac’s screen to match the room, making a white digital page look more like a physical piece of paper.
While many people find True Tone comfortable for reading text, it is disastrous for colour accuracy. If you are editing photos, watching movies, or doing any form of graphic design, your whites will often look slightly yellow or orange.
To ensure your screen colours are perfectly accurate and consistent, you should toggle True Tone to the Off position at the same time you disable auto-brightness.
Why Is the Auto-Brightness Option Missing?
Occasionally, you might open the Displays menu and find that the “Automatically adjust brightness” checkbox simply isn’t there.
This is completely normal if you are using a Mac Mini or a Mac Studio connected to a third-party external monitor (like an Asus or Dell screen). Because third-party monitors do not have Apple’s proprietary ambient light sensors built into them, the Mac operating system cannot detect the lighting in your room, and therefore automatically hides the setting entirely.
The setting is only available on MacBooks, iMacs, and Apple’s own premium external monitors (like the Studio Display or Pro Display XDR).
