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Comment by mrob | Hacker News Reader

>Many people don't care about FaceID or OLED screens.

The OLED screen is arguably a downgrade because it uses flickering PWM brightness control.

I’m not familiar with this. I have a X and haven’t noticed any flickering of the screen and really love it generally. Can you expand on this?

The OLED display on the X uses pulse-width modulation, which is basically where the OLED panel flickers at different frequencies to adjust its brightness. Most people (like me) don't really notice it, but for some it can cause headaches over prolonged use, and in some extreme cases really bad migraines.

Ah interesting. I definitely don’t notice it at all.

Nit pick. Pulse Width Modulation holds the frequency steady and varies the duty cycle, that is the ratio of on time to off time.

See here for more info: https://en.wikipedia.org/wiki/Pulse-width_modulation

Does this mean that the R, G and B values of any pixel is either 0 or 1 at any given instant? And how is it different from FRC: https://en.wikipedia.org/wiki/Frame_rate_control

Basically yes. But the frequency used for PWM is usually _way_ higher than what should be realistically visible to the human eye - If it was me, I'd probably use a couple of kilohertz.

Not sure how specifically it's done for OLED though.

Is PWM for varying the brightness of each pixel separately, or for adjusting the brightness of the entire screen? How are these two implemented generally on modern screens? Are PWM and FRC complementary or does one supersede the other? You can tell me about LCDs since you know them better.

At least on my Samsung Galaxy S3, turning the brightness to 100% stops the PWM flicker. If the current to each individual sub-pixel is also PWMed, it's done at a much higher frequency than the global brightness control PWM frequency.

I thought I was imagining it until I saw your comment. Interesting that some see it, while others don’t though.

I found it noticeable at first, it left my eyes feeling slightly tired and “scratchy” and the flicker was particularly noticeable in dark environments with low brightness (which probably makes sense, I guess the “off” part of the duty cycle is longer at lower brightness). I don’t notice it at all now, though I can still spot it if I look for it in a dark environment.

Can you cite any evidence that PWM results in either poorer image quality or a poorer experience?

I don't believe it exists, and I place this in the same category of people who think that wifi makes them sick.

Image quality is improved by PWM brightness, because the alternative is running at 100% duty cycle and changing brightness in software, which causes color banding because you're throwing away bit depth. Additionally, even slow (200Hz approx) PWM is well above the flicker fusion threshold for all humans, so no flicker is visible when your eyes are still.

The problem is phantom array effect artifacts when you move your eyes. These appear and disappear in response to eye movement, so they can be perceived as motion, which is distracting to some people. I personally find PWM very obvious and annoying, but I suspect I have unusually weak saccadic masking.

That's a big reason I didn't move to the XS. I use my phone on low brightness a lot, and the flicker is worse with brightness lower.

Is this intrinsic to oled, or will future versions be able to avoid this?

I use my X in a pitch black room on the lowest brightness setting a lot. I never notice any flickering. All I notice is a vastly better quality screen compared with every other prior iPhone device.

Take another smartphone, and point the camera at yours. Try the X on max brightness and at 10%. You should see some flicker in what the camera sees at 10% but not 100%.

You may not be bothered by it, mind you. I just tend towards dry/sensitive eyes and don't want to aggravate it.

I have very sensitive eyes with classic night blindness and an iPhone X. I don't think I've noticed any problems with headaches or eye strain. Did you notice them after usage or is it just a hypothetical outcome? Does the auto brightness control feature mitigate the problem or push it front end center? I'm curious as I also do not want to aggregate my situation.

I didn't use an X long enough. I didn't want to chance it. So, hypothetical.

However, you can use reduce white point and a higher brightness at night to avoid the flicker. Can be triggered with accessibility shortcut.

Cool, I will check out that setting and keep this in mind for future displays!

I also have really dry eyes pretty much year round (and I'm in Denver which unfortunately makes that worse!) and it's still no issue.

I have seen the videos (especially review videos) where the flicker on the camera is present from another camera, but I haven't noticed any eye strain or any problems with this device. If anything, I'm using it more than my previous ones because reading text on it is so enjoyable with the better screen.

Oh interesting. So, while this affects some people, it may not affect me.

The main people affected are those who get headaches, would you say? Maybe I should reconsider.

Your eyes become less sensitive to flickering in low light. That's how movie theaters could work at 24fps.

That's not to say no one can be bothered by it. But it's much less likely to bother anyone. I have sensitive eyes and tend to notice flickering at anything less than ~70hz. My Xs hasn't bothered me and I tend to use very low brightness even in well lit env.

Traditionally, movie theaters showed each analog film frame two or three times, so the flicker would be 48Hz or 72Hz, not 24Hz. 24Hz flicker is very obvious and annoying to everybody. Digital projectors might sample-and-hold like LCD displays and therefore have no flicker despite the low framerate.

See https://en.wikipedia.org/wiki/Movie_projector#Shutter

Huh? The screen on my X is noticeably better in so many ways from my prior generation iPhone.

Yeah. I thought I just had a busted phone—bad component somewhere, causing flickering. The fact that that's not recognized as a defect is shocking.

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