Re-posting this from yesterday to fix some typos and content issues :)

Part 1. AMOLEDs: do they all have ~100% modulation?

A few weeks ago, I made a post about how people should be careful when measuring OLEDs. Depending on the content on the screen, the measurement can be drastically different (and often completely incorrect). In the video, I used an iPhone app I made that let me display a small number of white rows to more accurately measure the flicker exhibited by each pixel. As I detailed in my post, measuring with the whole screen active will underestimate the modulation depth and distort the flicker waveform for OLEDs.

The famous OLED brightness dips seen in every OLED flicker measurement. This example is from my video where I showed that the iPhone 16 has nearly 100% modulation at max brightness.

The finding I shared in my video has now been replicated by others, including one person who reported their OnePlus 15R measured 95% modulation depth (also called flicker percent) at maximum brightness, instead of the commonly reported 5-10% modulation depth. u/Rx7Jordan tried the measurement technique on a Xiaomi 17 Pro Max and found 100% modulation depth on max brightness. I started to wonder, do any AMOLEDs actually have less than 100% modulation depth? People often call the dip in brightness from AMOLED a "refresh dip" or "PWM dip", but this isn't fully correct. OLED devices that do not use PWM (often TVs) still have this dip.

The "blanking" (brightness dip) occurs for two reasons:

1. Pixel compensation for display uniformity
2. Prevention of ghosting

Without compensation, OLED would have very poor color uniformity, especially as it ages (due to TFT threshold-voltage drift). This is known as OLED mura, and has been a known problem since before AMOLED was commercialized. Mura can show up as an issue even for compensated OLEDs. Without compensation, the problem would be bad enough that OLED would likely not be commercially viable. As such, I don't think any commercial AMOLED displays were produced without at least basic compensation. So even without PWM, the device needs to reconfigure the drive transistor so that compensation can be performed. This means that the pixel can't be driven during this phase.

Residual charge from the last frame has to be drained as well to prevent ghosting, which is a visual artifact seen when past frames leave faint afterimages. I think it's likely that OLEDs attempt to fully turn off each pixel during the compensation / refresh phase. I am proposing that every AMOLED device may have close to 100% modulation depth if measured correctly, and if so, then there may be no point in trying to select an OLED based on its modulation depth, and we should look at things like pulse width and frequency instead.

Kim, J.S., Lee, I.S., Park, J.Y. et al. LTPO-based pixel circuit with highly uniform luminance and low flicker for variable refresh rate in AMOLED displays. Sci Rep 16, 3865 (2026).

Here's a bit of the technical detail: In the image above, you can see a driver circuit for OLED pixels, from a 2025 paper. In (c), T6 is the transistor that shuts the OLED pixel off (called the emission transistor or EM), and T8 is the transistor that will discharge the pixel capacitance, causing it to go black. There are many different variations on the AMOLED pixel driver, but from what I can tell, they all have these features, meaning they should all drop to nearly complete darkness, resulting in high modulation depth at any device brightness.

I am interested to see if anyone can come up with an OLED device that has significantly less than 100% modulation depth (when measured in a way that isolates a small number of adjacent rows). I would think that if the pixels aren't fully discharged, the compensation would fail, and there would also probably be ghosting.

There is potential that an "externally compensated" OLED might not have this ~100% modulation, since these would not need to discharge the OLED storage cap to compensate. But to prevent ghosting, these devices need to discharge the OLED pixel anode, so they might also have nearly 100% modulation. I also don't believe DC-like dimming solves this issue, since it still needs the compensation phase where the pixels are shut off.

Part 2. I made an app to help people accurately measure OLED flicker.

I made this web tool that can be used with a flicker meter like the Opple LightMaster or TLM-110 to measure OLED flicker accurately: https://tools.sundiallabs.tech/test-mode/

Since my original post, a number of people have asked me for access to the app I used in the video to help produce the OLED test patterns. However, getting an app on the app store and porting it to Android is a lot of work. Until I have time to do that, I remade the app as a simple website that has almost all of the functionality of the app I used in the video.

The app allows you to create a test area on your screen of any color and height you choose. This lets you isolate a small number of rows when testing an OLED display, which is important for getting accurate flicker waveforms with a flicker meter. I'll provide more detailed info on my suggested measurement technique in a separate post, but I suggest trying to measure between 1 and 8 pixel rows when performing OLED flicker measurements. The reason for using more than one pixel row is that a few extra rows will give extra light, but won't affect the waveform significantly.

There are a few other features in the tool, including checkerboard patterns and gradients that can be used to look for various display artifacts. Please be aware that the checkerboard in particular could be visually stressful to some people.

If you try the site to help measure some of your OLED devices, please let me know and post your results below!

TM-39-25 is a document from the Illuminating Engineering Society that puts forth a classification system that seeks to reduce human responses to flicker. I often call the classification system itself "TM-39-25".

The system utilizes three different flicker effect visibility metrics, Mp, SVM, and PAVM. These metrics are scores computed from the flicker waveform that seek to predict the likelihood of a "temporal light artifact". I go over each metric in detail in the video, but here's a summary table:

https://preview.redd.it/wcv2st4dl8kh1.png?width=2720&format=png&auto=webp&s=959251de6d086b0e7e14ac6f2db3e2f29c9538ed

Simply put, a temporal light artifact is a visual disturbance of some kind due to flicker. TM-39-25 classifies light sources based on all three metrics simultaneously. I see this classification system as a vastly improved (but not perfect) replacement for IEEE-1789 classification, which are the frequently posted here as part of the results the Opple Light Master produces. Here's how the metrics scores map to the classifications:

https://preview.redd.it/eu77sdtkl8kh1.png?width=1505&format=png&auto=webp&s=bdaab419feb5c6a00f6c45dcbbc1bf5b39487d0b

I think this standard can be used as a replacement for the IEEE-1789 classification. The three metrics or "scores" it uses provide much more useful information and were created based on the results of experimental studies.

I have built this system into the flicker meter I'm working on (TLM-110), and used it to measure a variety of bulbs:

https://preview.redd.it/k6h1yilfk8kh1.png?width=2300&format=png&auto=webp&s=4bc5c3624bc7fd71a4c7f82ab347d5ebf3180e51

You can see there's a wide range of classifications in the bulbs I tested, as well as a large spread in the scores. The bulbs that are "Not Recommended" are unbearable to me, while the bulbs that are "Better" are much more tolerable.

I think this system has the ability to be broadly useful, especially for non-experts. However it isn't perfect. Firstly, while it technically applies to all light sources (displays included), it is most relevant to lighting such as bulbs and lamps. There are likely screen-specific flicker effects that haven't been described yet. Also, it mainly predicts the visibility of flicker artifacts, which are visual disturbances, not health effects. I think flicker artifacts and visual disturbances may be correlated, but there is not a one-to-on relationship.

Thanks to u/Rx7Jordan for making me aware of this standard.

I've been looking for a decent phone that I can replace my current iPhone 16 with, since I can only tolerate it for a few minutes a day. I've been looking at a lot of OLED test reports, and I think I've noticed a problem with many of them: the measured flicker is falsely low, since the photodiode is measuring multiple OLED rows at once. In my opinion this results in a loss of information about what the screen is really doing.

In some extreme cases, I've seen devices which actually have 100% modulation depth be measured at ~5% modulation depth. All the OLEDs I've measured with this method (using my meter or the Opple) actually show 100% modulation depth at all brightness settings. I'm not confident this is true for EVERY device, but I think there are a lot of measurements online that underestimate the OLED flicker.

I showed this in the video, but to avoid this error you simply have to reduce the number of OLED scanning rows that the flicker meter detector is exposed to. Ideally, we'd only measure one row since this contains all the relevant information. In practice multiple rows are needed to get enough light onto the detector.

For me, it might be time to just buy an e-ink phone.

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).