u/BearNecessary4141

I created a visualization of how many OLEDs actually flicker and use PWM: https://www.sundiallabs.tech/pages/oled-flicker

I made this because I was inspired by a post by u/NoFlickerPhone, who made a great PWM simulation webpage. The goal of my page is to explain how and why OLEDs flicker, and also describe how to properly measure OLED flicker. I've been doing lots of flicker measurements on OLEDs lately, and it can be confusing to get right. I've also seen lots of PWM test results on OLEDs that were not done completely correctly and end up underestimating the flicker depth. Incorrect results are especially common to see at high / moderate brightness.

The first visualization shows how the dimming works on mobile OLEDs, specifically modeled after the iPhone 17 Super Retina XDR OLED. It appears to use DC-dimming for some of the brightness range, then switch to PWM. This is done because most OLEDs can only be DC-dimmed to a certain point.

The second visualization explains why OLEDs need to be measured carefully. The basic idea is that if your measurement device is detecting light from multiple rows, the waveform will be "smeared" or averaged and the flicker will look less bad than it actually is. This averaging isn't what our eyes do (they form an image of the screen which preserves the flicker pattern). So ideally, we need to be measuring the flicker from a single row (or only a few adjacent rows).

https://youtu.be/xYikB5m553E?si=N27FGTIbop_S8pg5

I did some testing on various reading lights (book lights), some cheap, some expensive. I found that even reading lights sold as PWM-free still have high frequency PWM (often around ~1-5 kHz). This is especially true of book lights that have multiple brightness settings. Based on what we know about phantom array effects and stroboscopic effects, I don't think it's ideal to have a light that flickers at multi-kHz frequencies. We know that PWM at these frequencies is detectable by our visual system, but we don't have enough data to understand the health effects.

When we read, we make fast eye movements across the page (saccades) that allow our visual systems to detect flicker / PWM at frequencies we can't usually detect. We know that low frequency flicker can cause the visual system to "overshoot" when reading which results in eye strain. Historically, high frequency (>1 kHz) flicker was thought to be benign, but this idea is largely based on findings for sources with low modulation depths. LEDs often have close to 100% modulation, which does seem to produce visual effects event at high frequencies when studied.

I think we should aim for reading lights (including those used with e-ink devices) that have a PAVM (phantom array visibility measure) and SVM (stroboscopic visibility measure) of less than 0.1, which should adequately minimize the risk for most people.

I've tested dozens of reading lights (I'll make a full post with results soon) and found that the best way to search for PWM-free reading lights is not using the terms "zero flicker" or "PWM-free" but instead looking for "constant current driven". Ideally, ask the manufacturer specifically if it's driven by a constant current driver. And of course, it's ideal to measure flicker meter; some of the reading lights I've tested were sold as flicker free but upon testing had 500 Hz - 1 kHz flicker.

OLED Flicker Visualization (iPhone 16/17): Understanding and Measuring OLED Flicker