[demosthanos]

> The frequency of 239 Hz is relatively low, so sensitive users will likely notice flickering and experience eyestrain at the stated brightness setting and below.

Do you have a source for this claim that 239 Hz is low enough to be noticeable by some measurable fraction of people? People report being sensitive to all kinds of things that end up repeatedly failing to reproduce empirically when it's put to the test (e.g. WiFi and MSG), so that there's a PWM sensitivity subreddit is not the evidence that TFA thinks it is.

The source that TFA links to backing up the idea that between 5% and 20% of people are sensitive to PWM flickering is a Wikipedia article which links to a Scientific American article which does not contain the cited numbers, and even if it did the study it discusses was researching the significantly slower 100 Hz flickering of fluorescent bulbs.

[_3yjt]

Here is one: https://www.nature.com/articles/srep07861

They mentioned in Results section: > For the median viewer, flicker artifacts disappear only over 500 Hz, many times the commonly reported flicker fusion rate.

[demosthanos]

Yes, that's an interesting source that at least shows that our eyes can perceive things at those high frequencies, but I'm not sold that it generalizes.

The study actually demonstrates that perception of flicker for regular PWM does in fact trail off at about 65 Hz and is only perceptible when they create the high-frequency edge by alternating left/right instead of alternating the whole image at once.

It looks like the situation they're trying to recreate is techniques like frame rate control/temporal dithering [0], and since this article is now 10 years old, it's unclear if the "modern" displays that they're talking about are now obsolete or if they actually did become the displays that we're dealing with today. From what I can find OLED displays do not tend to use temporal dithering and neither do nicer LCDs: it looks like a trick employed by cheap LCDs to avoid cleaner methods of representing color.

It's an interesting study, but I don't think it redeems TFA, which isn't about the risks of temporal dithering but instead claims harms for PWM in the general case, which the study you linked shows is not perceived above 65 Hz without additional display trickery.

[0] https://en.wikipedia.org/wiki/Frame_rate_control

[_3yjt]

What they are trying to do is recreating the situation that is more similar to actual light sources in computer screens and TV (varying flickering rate from different pixels/ areas). They are saying that the current threshold of 65Hz commonly reported are tested on light sources that are uniformed in flickering, which is not the case for actual screens. It is not about dithering.

Basically the claim is that when there are varying flickering frequency, the requirements for non-flicker frequency is much higher.

[demosthanos]

No, they're specifically contrasting two types of displays and identify that the traditional way of measuring flicker effect does work for the traditional displays, regardless of image complexity:

> Traditional TVs show a sequence of images, each of which looks almost like the one just before it and each of these images has a spatial distribution of light intensities that resembles the natural world. The existing measurements of a relatively low critical flicker fusion rate are appropriate for these displays.

> In contrast, modern display designs include a sequence of coded fields which are intended to be perceived as one frame. This coded content is not a sequence of natural images that each appears similar to the preceding frame. The coded content contains unnatural sequences such as an image being followed by its inverse.

What's unclear to me 10 years down the road is if the type of display they're worried about is common now or obsolete. "Modern" in 2015 could be the same as what we have today, or the problems the study identified could have been fixed already by displays that we would call "modern" from our reference frame.

I don't know enough about display tech to comment on that, but they're very clear that if your display is showing frames in sequence without any weird trickery that the research method that gets you a 65 Hz refresh rate is a valid way to test for visible flickering.

EDIT: Here's another quote that makes the contrast that they're setting out even more clear:

> The light output of modern displays may at no point of time actually resemble a natural scene. Instead, the codes rely on the fact that at a high enough frame rate human perception integrates the incoming light, such that an image and its negative in rapid succession are perceived as a grey field. This paper explores these new coded displays, as opposed to the traditional sort which show only a sequence of nearly identical images.

It's possible that this is actually a thing that modern displays have been doing this whole time and I didn't even know it, but it's also possible that this was some combination of cutting-edge tech and cost-saving techniques that you mostly don't need to worry about with a (to us) modern OLED.

[_3yjt]

That is just the motivation, the experiment is much more general and is not related to display technology:

> The work presented here attempts to clarify “the rate at which human perception cannot distinguish between modulated light and a stable field

Otherwise, they would have tested the dithering directly for the full image. Here they are testing a more simpler model: varying flickering causes higher flickering-free requirements (due to eye movements). This would applies to dithering, but potentially other situations.

[demosthanos]

You can't say "that is just the motivation", because the motivation is what dictated the terms of the experiment. I read the whole study: the contrast between the two types of displays permeates the whole thing.

They repeatedly say that the goal is to measure the effect of flickering in these non-traditional displays and repeatedly say that for displays that do not do the display trickery they're concerned about the traditional measurement methods are sufficient.

You're correct that they do demonstrate that the study shows that the human eye can identify flickering at high framerates under certain conditions, but it also explicitly shows that under normal conditions of one-frame-after-another with blank frames in between for PWM dimming the flickering is unnoticeable after 65 Hz. They go out of their way to prove that before proceeding with the test of the more complicated display which they say was meant to emulate something like a 3D display or similar.

So... yes. Potentially other situations could trigger the same visibility (I'd be very concerned about VR glasses after reading this), but that's a presumption, not something demonstrated by the study. The study as performed explicitly shows that regular PWM is not perceptible as flicker above the traditionally established range of frame rates, and the authors repeatedly say that the traditional measurement methods are entirely "appropriate" for traditional displays that render plain-image frames in sequence.

EDIT: Just to put this quote down again, because it makes the authors' point abundantly clear:

> The light output of modern displays may at no point of time actually resemble a natural scene. Instead, the codes rely on the fact that at a high enough frame rate human perception integrates the incoming light, such that an image and its negative in rapid succession are perceived as a grey field. This paper explores these new coded displays, as opposed to the traditional sort which show only a sequence of nearly identical images.

They explicitly call out that the paper does not apply to traditional displays that show a sequence of nearly identical images.

[user_7832]

> People report being sensitive to all kinds of things that end up repeatedly failing to reproduce empirically when it's put to the test (e.g. WiFi and MSG), so that there's a PWM sensitivity subreddit is not the evidence that TFA thinks it is.

I know you’re looking for large sample size data, but PWM sensitivity absolutely exists, and I wish it didn’t. The way my eyes hurt in less than a minute while looking at an OLED phone (when I can handle an LCD phone for hours just fine) is too “obvious”. This occurs even on screens I didn’t know were OLED till I got a headache, btw.

(I’m also insanely sensitive to noticing flicker and strobe lights - I say a light flickers, everyone disagrees, I pull out the 240fps mode on my phone… and I’ve never been proven wrong till now.)

[gblargg]

I used a 240 Hz PWM-dimmed monitor for a couple of years and I adjusted, but when I switched to a flicker-free one, it was very noticeable and bothersome to use the old one. Even though it's not perceptible when looking at a fixed point, when moving one's eyes around the after-images are easy to see. Even 1000 Hz PWM-dimmed LED strips are easy to notice when looking around the room. The light is basically being panned across one's retina like a panoramic camera/oscilloscope, logging its brightness versus time.