Fix Screen Flicker Headaches on MacBook (2026 Guide)

MacBook screen flicker comes from two invisible display mechanisms: PWM backlight dimming (a backlight switched on and off far faster than you can see) and temporal dithering (pixel-level color alternation on all Apple Silicon Macs). Restarting, resetting SMC, or turning on Night Shift won’t change either one. Sundown works on both mechanisms in one app, because its Flicker-Free Mode holds the backlight at full power and dims through the gamma table instead, and its anti-dithering mode goes after the pixel-level alternation.

Twenty minutes into the workday you start to feel a pressure behind your eyes that wasn’t there when you sat down, and by lunch it has spread into a dull ache across your forehead. You’ve been to the optometrist and your prescription is fine, and you’ve tried the 20-20-20 rule, adjusted your chair height and cleaned your screen, but none of it has helped. (If your symptoms go wider than flicker, with dry eyes, blurred vision or tension headaches, read our guide to reducing eye strain on Mac, which covers all seven root causes.)

So this post goes through both of them, which models are affected, and why the generic fixes the internet keeps recommending don’t work.

PWM Flicker: The Strobe You Can’t See

You would expect your MacBook to dim its screen by having the backlight produce less light, since that’s the intuitive way to do it, but that isn’t how it works. It uses a technique called Pulse Width Modulation, or PWM.

Picture a ceiling fan with a strobe light attached. To make the room look dimmer, the light doesn’t glow at a lower wattage; it blinks on and off so fast that the room looks less bright on average. At 50% brightness the light is fully on for half of each cycle and fully off for the other half, and your eyes see the average.

On a display that uses it, the backlight runs through this on-off pattern far faster than you can see. That sounds fast enough to be harmless, although for some people it may not be.

What the flicker and eye strain studies do and do not show is collected in Screen Flicker and Digital Eye Strain: The Evidence.

On a display that dims with PWM, the off phase of each cycle gets longer the lower you set the brightness.

Temporal Dithering: The Second Flicker Nobody Talks About

PWM gets the occasional mention in tech forums, but temporal dithering almost never does, even though the two are entirely separate sources of display instability.

Your MacBook’s display panel can physically render a certain number of distinct color values per pixel. To show a color that falls between two of those values, macOS alternates the pixel rapidly between the two neighboring colors, frame by frame, and your eye blends the alternation into the shade in between. You get smoother color gradients, and the price is per-pixel flickering across the entire display surface, every frame, all the time.

That makes it a different thing from PWM. PWM is the backlight turning on and off, while temporal dithering is individual pixels changing color values, so you end up with two independent sources of visual instability layered on top of each other.

At standard color temperatures the dithering is subtle. Push the display toward deep warm tones, though, which is exactly what blue light filter apps do after sunset, and the dithering shows up as a crawling noise pattern across the screen. On a display that also dims with PWM, that makes two flicker sources at once: the backlight strobing far faster than you can see, and every pixel on the panel shifting values at your refresh rate.

Which MacBooks Are Affected (And How to Test Yours)

Some MacBook displays dim the backlight with PWM, and whether yours does depends on the model (NotebookCheck found it on the 2020 MacBook Air's Retina display).

Older Intel MacBooks: PWM characteristics vary by model year, and Sundown’s anti-dithering switch works on Apple Silicon only.

You can test your own display with your phone. Open the camera in slow-motion mode (240fps if you have it) and point it at your MacBook screen with the brightness set to 30%. Horizontal bands rolling across the display in the recording are PWM, because what you are seeing is the camera catching the backlight’s on-off cycle.

Temporal dithering is harder to capture on camera. The easiest visual test is to push any blue light filter app to its deepest red setting and look at the solid areas of color, because a shimmering, sand-like noise pattern there is temporal dithering making the color alternation visible.

How to Fix Screen Flicker Headaches on MacBook: 7 Myths Debunked

1. Restart your Mac. PWM is how the hardware behaves, so there is no software glitch for a restart to clear, and restarting changes nothing about how the backlight modulates brightness.

2. Reset SMC / NVRAM. These resets affect power management and startup settings, whereas the display’s PWM frequency is set by the LED driver IC on the display board, which no software reset touches.

3. Disable True Tone. True Tone adjusts color temperature to match the ambient light and has no effect on PWM frequency, duty cycle, or temporal dithering. Turning it off changes how warm or cool your screen looks, and that’s all it changes.

4. Update macOS. The flicker frequency is set by the hardware.

5. Use Dark Mode. Dark Mode changes the color of interface elements and leaves the backlight alone, so your display still uses PWM whether the pixels are showing white or black content.

6. Enable Night Shift or install f.lux. We compared these tools in our Night Shift vs f.lux breakdown, and our guide to installing f.lux on a Mac covers setup. Both change color temperature and neither changes how the backlight controls brightness, so Night Shift at its warmest with PWM is the same PWM, just warm white, and f.lux at its warmest with PWM is the same PWM, just deep orange. If you're looking for a Night Shift alternative for Mac that does address flicker, Sundown pairs blue light filtering with a Flicker-Free Mode that dims through the gamma table instead of the backlight.

7. Adjust brightness manually. Brightness changes how long PWM’s off phase lasts, but it does nothing about temporal dithering, which runs at every brightness level.

What the Science Says: IEEE 1789 and Flicker Frequency Thresholds

IEEE 1789-2015 is the Institute of Electrical and Electronics Engineers’ standard for evaluating health risks from LED flicker. It counts flicker above 1,250 Hz as low risk, which is low risk rather than no risk.

Research by Wilkins and colleagues, whose work informed the IEEE standard, studied how flicker relates to headaches in sensitive people.

Software Solutions Compared: BetterDisplay vs StillColor vs Sundown

Three macOS applications deal with display flicker.

BetterDisplay is a display management utility with a PWM avoidance feature that works by setting a brightness floor. You configure it never to let your hardware brightness drop below a certain level, which is meant to keep the backlight out of the range where it dims with PWM. That avoids PWM dimming, and since version 2.3.0 it can also switch off GPU dithering on Apple Silicon.

StillColor is a small, focused utility aimed at temporal dithering and nothing else. It changes how macOS renders color values so that Apple Silicon GPUs don’t apply the frame-by-frame pixel alternation, and it is free and good at that one job. It doesn’t touch PWM at all, though, so if your macbook screen hurts your eyes and the cause is backlight flicker and not pixel dithering, StillColor won’t help.

Sundown works on both. Its flicker-free mode holds hardware brightness at maximum and dims the screen through the gamma table, so the dimming doesn’t rely on the backlight’s PWM, and its anti-dithering mode targets temporal dithering on Apple Silicon. It also adds blue light filtering down to a deep red, which cuts back the short-wavelength light that Harvard Health describes as the strongest melatonin suppressor.

Sundown also warms the screen, down to a deep red. Start your 7-day free trial at trysundown.com.

How Sundown’s Flicker-Free Mode Works

Sundown handles PWM differently from a plain brightness lock. When you turn on flicker-free mode, the app tells macOS to hold the hardware backlight at 100% brightness. With the backlight at full power, the dimming no longer depends on turning the backlight down, which is where PWM’s off phase grows longest.

A screen at 100% hardware brightness would be blinding, so Sundown dims the image through the gamma lookup table, the same mathematical transform macOS uses to map pixel values to display output. Adjusting the gamma curve lowers the perceived brightness of every pixel without ever touching the backlight.

For temporal dithering, Sundown’s anti-dithering feature talks to the Apple Silicon display coprocessor through IOKit and sets the framebuffer property enableDither to false. The display coprocessor then stops applying temporal dithering, so pixels that would normally alternate between two values snap to the nearest available value and stay there, without the sand-grain shimmer.

The app sits in your menu bar and stays out of your way, so you pick a warmth, turn on the modes you need, and get back to work.

Quick Reference: MacBook Flicker Types and Fixes

Sundown addresses both mechanisms in a single app. For more on eye comfort, see our guide to Apple Silicon display dithering, our comparison of f.lux alternatives for Mac, and our complete guide to MacBook blue light filters. Our comparison of every Mac display health app covers how each handles flicker, our roundup of Mac screen dimmer apps covers the brightness side of the same discomfort, and our science page goes into light and sleep.

FAQ

What is the difference between PWM flicker and temporal dithering on MacBooks?
PWM controls screen brightness by switching the backlight on and off far faster than you can see, and the lower the brightness, the longer the off phase. Temporal dithering simulates color depth by alternating individual pixel color values between frames. PWM is something the backlight does and dithering is something the GPU does when it renders, so they are independent sources of flicker and fixing one does not fix the other.

Does keeping MacBook brightness at 100% stop PWM headaches?
It depends on the model. Whether a MacBook display dims with PWM, and how, varies from model to model (see the section on affected MacBooks above). Brightness also does nothing about temporal dithering, which runs at every level on Apple Silicon.

What Hz frequency is safe for screen flicker?
IEEE 1789-2015 classifies frequencies above 1,250 Hz as “low risk.” There is no single “safe” frequency that removes the risk for every user. The approaches aimed at avoiding backlight PWM are DC dimming, or software-based brightness reduction that keeps the backlight at a steady level. If you are choosing an external monitor, PWM Monitor Flicker: Why Your Screen Hurts covers how to test one for PWM.

Your screen may be flickering in two separate ways at once, and a restart won’t change either of them. Sundown starts at $4.99/mo (or $79 lifetime) and works on both PWM and temporal dithering in a single app. Start your 7-day free trial at trysundown.com.

Further reading

• Computer vision syndrome on a Mac: the other reasons a screen can leave your eyes tired.
• Blue light filters for a computer screen: software, screen protectors and built-in modes compared.