A MacBook that keeps changing brightness is almost always reacting to one of 6 things: the ambient light sensor, True Tone, battery dimming, Low Power Mode, the idle timer, or an app. Each has its own switch in System Settings.
Why does my MacBook keep dimming?
Match what you see to the cause, then use the switch in the last column.
New macbook air M2 brightness keeps changing
“Hi, I just got my first ever mac, I have an issue with the brightness, it keeps changing automatically whenever I close the lid and open it back again.”
| What you see | Cause | Where to change it |
|---|---|---|
| Brightness drifts as the light around you changes | Automatically adjust brightness (ambient light sensor) | System Settings > Displays |
| Colors turn warmer or cooler and the screen looks dimmer | True Tone (or Night Shift on a schedule) | System Settings > Displays |
| Screen dims the moment you unplug | Slightly dim the display on battery | System Settings > Battery > Options |
| Screen dimmer on battery or after changing power settings | Low Power Mode | System Settings > Battery (or Control Center on macOS Sequoia 15.1 and later) |
| Screen goes dark after a few idle minutes | Turn display off when inactive, or the screen saver | System Settings > Lock Screen |
| Brightness jumps when an app opens, closes or plays video | An app, or HDR video on screen | Quit the app or pause the video to test |
How do I turn off auto brightness on a Mac?
Open System Settings from the Apple menu.
Click Displays in the sidebar.
Turn off Automatically adjust brightness.
Set brightness by hand with the slider or the brightness keys.
The switch only appears on Macs with an ambient light sensor. Apple describes the feature as adjusting brightness "based on current ambient lighting conditions" and notes that turning off auto-brightness "may affect battery life, energy consumption, and long-term display performance." If you mostly work in one steady light, leaving it on is fine. If you move between shade and sun, or the changes distract you, turn it off and set the level yourself.
The sensor reacts to light you may not notice yourself. One MacBook owner on MacRumors had a screen that dimmed and brightened while they typed, and found the cause the next day:
“Apparently it automatically adjusts to light. So when I was in the library all day it was the same light and everything was fine. In my room it was adjusting to the pockets of light and shadow as I was moving around.”- A MacBook owner on MacRumors Forums, July 2015
Does True Tone change brightness?
True Tone changes the color of the screen to match the light around you, not the brightness level. When it shifts whites toward warm, the screen can look dimmer, especially outside next to a bright sky. Turn it off in System Settings > Displays to test. Night Shift, in the same place, warms the screen on a schedule, so a screen that changes at the same time every evening is usually Night Shift.
Why does my MacBook dim when I unplug it?
On a MacBook, System Settings > Battery > Options has Slightly dim the display on battery. With it on, the screen steps down each time you unplug and back up when you plug in. Turn it off if you want the same brightness either way.
Low Power Mode is the other battery setting that lowers the screen. Apple says it "reduces energy use to increase battery life" (About Power Modes), and when Apple brought it to the Mac it said it reduces the display brightness. You can set it to run only on battery, always, or never in System Settings > Battery, and on macOS Sequoia 15.1 and later from Control Center.
The same Options sheet also has "While on battery power, play high-dynamic-range (HDR) video in standard dynamic range (SDR)". It changes how HDR video plays on battery, not the rest of the screen.
Why does my MacBook screen go dark after a few minutes?
A screen that goes dark after a few idle minutes is following the idle timer, not the brightness setting. In System Settings > Lock Screen, Turn display off on battery when inactive and Turn display off on power adapter when inactive set how long the Mac waits before the screen saver starts or the display turns off (Apple's Lock Screen settings). Choose a longer time if the screen goes dark while you are reading.
Why does brightness still change with auto-brightness off?
Then another setting is doing it. A MacBook Pro owner on MacRumors Forums had turned off both Automatically adjust brightness and Slightly dim the display on battery in 2025: "Yet, the brightness still self adjusts and as soon as I unplug my MBP, the screen dims a bit." Work through these in order.
Check Low Power Mode in System Settings > Battery. Set to run only on battery, it lowers the screen the moment you unplug, even with battery dimming off.
Quit display and brightness apps one at a time, and pause any video.
Try a new user account. Create a test account in System Settings > Users & Groups and log in to it. If the brightness holds steady there, a setting or app in your own account is the cause.
Update macOS in System Settings > General > Software Update.
On an Intel MacBook, reset the SMC. Apple's SMC reset steps note that "SMC resets automatically on Mac with Apple silicon", so on those a restart does the same job.
Why is my brightness adjustment not working?
If the brightness keys do nothing, they may be set to work as F1 and F2: hold the fn (Globe) key while you press them, or turn off "Use F1, F2, etc. keys as standard function keys" in Keyboard settings (Apple's keyboard guide). The Display slider in Control Center works either way. On a 14- or 16-inch MacBook Pro, a studio Preset in System Settings > Displays can also limit the controls; Apple says "the number of options available in Displays settings changes or is limited, depending on the mode you select" (Use the Preset menu). Most external monitors set brightness with their own buttons, not the Mac keys.
Can an app change my MacBook brightness?
Yes. Display managers such as BetterDisplay and Lunar can set brightness themselves, and HDR video in a browser or player can make the rest of the screen look dim next to its highlights. To test, quit display and brightness apps one at a time and pause any video.
Brightness apps that go past the slider change the screen only when you turn them on. Outshine for Mac, for example, switches on and off with Option-Command-O, and its optional "Suggest Blazing when bright" setting offers a one-tap switch to the Blazing preset when it gets brighter around you; it never switches by itself. If the screen changes when you didn't expect it, check the menu bar for any app that is on.
Should you keep brightness steady when working outside?
Outside, a steady full brightness usually serves you better than a sensor that reacts to every cloud. One Mac user on MacRumors Forums put it simply: "Personally, I don't like my monitor brightness changing when the sun goes behind a cloud…so I turn that stuff off and just adjust it myself when I need to." Turn off auto-brightness, turn off battery dimming, keep Low Power Mode off while you need the full screen, and set the slider to the end. Why that still may not be enough in direct sun, and what helps next, is in MacBook at full brightness but still too dark and MacBook Air brightness, explained.
When the slider is at the end and daylight still washes the screen out, Outshine for Mac adds brightness past it using the reserve macOS keeps for HDR video (EDR). Its Reading and Outdoor presets lift white pages and backgrounds and leave text and dark interface alone. Reading is the preset Mickey Switzer, who makes Outshine, uses most: it aims at easy reading rather than full brightness. The lift is largest on a 14- or 16-inch MacBook Pro with Liquid Retina XDR and smaller on a MacBook Air. Without a license it works on the left half of the screen with no time limit.
The Mac app that handles all of this for you.
Four presets - Reading, Outdoor, Blazing and Dark - for every kind of light. Switch from your menu bar in one click. No settings archaeology.
- System Settings > Displays: Automatically adjust brightness off, True Tone off, Night Shift schedule off.
- System Settings > Battery > Options: Slightly dim the display on battery off.
- System Settings > Battery: Low Power Mode set to Never (or only when you don't need full brightness).
- System Settings > Lock Screen: a longer time before the display turns off.
- Menu bar: no display or brightness app changing things you didn't ask for.
Questions people ask
Why does my MacBook keep dimming by itself?
Usually Automatically adjust brightness in System Settings > Displays, which follows the ambient light sensor. Other causes are Slightly dim the display on battery (System Settings > Battery > Options), Low Power Mode, True Tone, and the idle timer in System Settings > Lock Screen.
How do I turn off auto brightness on a Mac?
Open System Settings, click Displays and turn off Automatically adjust brightness. Then set the level with the slider or the brightness keys.
Why does my MacBook brightness change when I unplug it?
The setting Slightly dim the display on battery is probably on. Turn it off in System Settings > Battery > Options, and check that Low Power Mode isn't set to run on battery.
Why are my MacBook brightness keys not working?
The top-row keys may be set to act as F1 and F2. Hold the fn (Globe) key while pressing them, or turn off "Use F1, F2, etc. keys as standard function keys" in Keyboard settings. The Display slider in Control Center changes brightness either way.
Why does my Mac screen look washed out?
Outside, daylight reflecting off the glass washes the picture out; tilt the screen and set brightness to full. Indoors, check System Settings > Accessibility > Display for a lowered Display contrast slider or a color filter, and choose the recommended Color profile in System Settings > Displays.
Does Outshine change my MacBook brightness on its own?
No. Outshine for Mac changes the screen only when you turn it on, with the menu-bar icon or Option-Command-O. Its optional Blazing suggestion is a one-tap prompt and never switches by itself.
Read next: Make a MacBook brighter than max, How to see your MacBook screen in sunlight and The outdoor laptop setup, start to finish.