PWM Dimming Flickers Your Screen Faster Than You Can See It

A 2025 study in the Journal of the Optical Society of America A put an oscillating arm in front of an OLED smartphone display and asked observers whether they could see a stroboscopic effect. The effect was visible when the dimming frequency was 480 Hz and 960 Hz with the display luminance below 40 cd/m². Above 960 Hz, it disappeared. That threshold is the whole problem in one number.

PWM dimming is a way of controlling screen brightness by switching the light source on and off very quickly. The percentage of time the light is on is the duty cycle. Your eye averages the pulses into what looks like a steady, dimmer image. The flicker is real, but it happens faster than conscious perception. Some people feel it anyway.

The OLED constraint that made PWM necessary

Liquid crystal displays have a backlight. The backlight is always on, and the liquid crystals in each pixel act as shutters, controlling how much of that light reaches your eye. To dim an LCD, you can simply reduce the backlight current. The light source gets less power, it produces less light, and the color stays consistent. This is called DC dimming, and it has been the standard for LCD screens for decades.

OLED displays have no backlight. Every pixel is its own light source. To dim an OLED, you might think you could reduce the current through each pixel the same way. But you cannot, because the color changes. A 2019 analysis from Notebookcheck explains the problem: if you feed less voltage to the organic diodes, they not only limit their brightness, but their color also changes. The red, green, and blue subpixels do not respond to voltage reduction at the same rate, so a dimmed OLED shifts its white point and loses color accuracy.

The industry’s solution was to stop reducing the current. Instead, PWM dimming keeps the pixel current at its nominal level and switches the pixel on and off rapidly. At 30 percent brightness, the pixel is on for 30 percent of each cycle and off for 70 percent. The current is always either full or zero, so the color is consistent across all brightness levels. The TI video on PWM dimming explains the trade-off plainly: PWM minimizes color shift that can occur during analog dimming, but it adds complexity to the design.

The frequency is where the trouble starts

The flicker from PWM is invisible to the human eye if the frequency is high enough. A TI technical article states that the dimming frequency must be faster than the human eye can detect, 200 Hz or above, to prevent visible flickering. But visibility is not the same as biological effect. The PNNL’s 2022 review of flicker research explains that PWM introduces rectangular modulation with high Fourier frequency content, which can increase unwanted responses, especially among more sensitive individuals who are more likely to experience eyestrain, headaches, or migraines in their daily activities.

The IEEE published a standard in 2015 to address this. IEEE 1789-2015, Recommended Practices for Modulating Current in High-Brightness LEDs for Mitigating Health Risks to Viewers, defines modulation frequencies and recommends limits. The standard’s low-risk threshold is a percent flicker of less than 9.6 percent, according to a California Energy Commission filing that references the standard. At frequencies below 90 Hz, the allowed modulation is even lower. The standard exists because there was no guidance before it, and vendors were choosing frequencies with no common reference.

The phone measurements tell the story

Not all PWM is the same. Notebookcheck measures the PWM frequency of every phone it reviews, and the 2026 results show wide variation between manufacturers. The Samsung Galaxy Z Fold8 Ultra uses a PWM frequency of 240 Hz to 480 Hz. The Vivo X Fold6 uses 1,920 Hz. The Honor Magic V6 uses 4,320 Hz. Motorola’s Razr Fold uses DC dimming by default and switches to PWM at 720 Hz below 30 percent brightness.

The difference between 240 Hz and 4,320 Hz is the difference between a flicker that some people can feel and one that almost no one can. The 2025 stroboscopic study found that the effect was visible at 480 and 960 Hz below 40 cd/m², which means the Samsung display at 240 to 480 Hz is in the range where sensitive users may notice it. The Honor display at 4,320 Hz is far above the threshold where the stroboscopic effect disappears.

A 2025 IEEE conference paper compared PWM and DC dimming on visual function. At a brightness of 45 to 55 nits, PWM dimming had a significantly greater impact on ocular imaging quality than DC dimming during continuous visual tasks. The paper also found that the difference in visual fatigue indices between the two technologies was not statistically significant, which suggests that the measurable optical effects do not always translate into reported discomfort. The science is still working out the relationship between the physical flicker and the subjective experience.

Why some people feel it and others don’t

The variation is real. The PNNL review notes that individuals with visual sensitivity may exhibit alterations in their response to temporal light modulation. The same flicker that one person never notices can trigger a migraine in another. The mechanism is not fully understood. The 2025 IEEE paper suggests that PWM’s high-frequency brightness oscillations affect the eye’s wavefront aberration distribution, including spherical aberration and coma, which degrades retinal image quality. But the cumulative effect on retinal neural adaptation fatigue appears similar to DC dimming.

The practical implication is that you cannot rely on a specification sheet to know whether a phone will bother you. You have to look at one. If you are sensitive to flicker, the PWM frequency is the number to check. Higher is better. Above 2,000 Hz is good. Above 3,000 Hz is better. The Honor Magic V6 at 4,320 Hz is the current benchmark among the phones Notebookcheck has measured.

What changed and what to check

DC dimming is not a perfect fix. A Xiaomi support page explains that enabling DC dimming can result in color gradient loss at low brightness levels, because the OLED pixels lose color accuracy when you reduce their voltage. Some manufacturers use a hybrid approach: DC dimming at high brightness, PWM at low brightness. Motorola does this on the Razr Fold, switching to PWM below 30 percent. Xiaomi’s 15T uses DC dimming at high brightness and PWM at 3,840 Hz at low brightness.

The direction of travel is clear. High-frequency PWM is the current solution, and the frequencies are going up. If you are shopping for a phone and you care about flicker, look for a measured PWM frequency above 2,000 Hz. If you already have a phone that bothers you, try raising the brightness. The flicker is worst at low brightness, and the stroboscopic effect study found that the effect was only visible below 40 cd/m². Turning the brightness up moves you out of the range where the flicker is most noticeable.