I believe I have found a method to test computer monitors, TVs, phones, laptops, etc. for headache-inducing flicker using a powerful photodetector (Thorlabs PDA100A2) and oscilloscope. It can zoom 3000x, which I believe is way beyond what anyone on this forum has used. Hats off to @KM who had mentioned it in a previous post and also described how to build a DIY device that I’ve been using. Like many on this forum, I have a handful of devices that work for me and a growing junkyard of devices that I thought would be usable but in fact give me headaches. So I set about looking at each of my screens using the Thorlabs photodetector to see if I could tell the difference between the screens that give me headaches and the screens that do not. When I zoomed to 100x magnification, I was able to see significant differences in the amount of flicker between screens that bother me and screens that do not. I then went to Best Buy and spent about 3 hours wandering the store testing 100+ devices (phones, TVs, laptops, etc.) in search of truly flicker-free devices. I was able to find about five laptops/chromebooks, one iPad, zero TVs, zero phones, and zero computer monitors. Let me try to boil it all down to three screen shots: My trusty Dell 5567 laptop that I’ve been using for five years without symptoms. There is barely any flicker. A used Dell 5567 that I bought a few weeks ago as a backup. I cloned the SSD drive, so everything should be the same. But this one gives me headaches within minutes. The flicker is clearly visible. An example flicker-free device that I found at Best Buy, just to prove that such a thing exists. This happens to be a laptop that I went ahead and ordered but have not yet received. I really want to get some more people involved in this as I think this testing could have a huge impact. I have two ideas, but I’m sure there are others I’m not thinking of. Idea #1: If someone with a variety of good and bad devices is willing to repeat my experiment, I’m happy to loan you my equipment. It’s not terribly difficult, but there are some steps that must be followed precisely. If you’re good at things like setting up your home theater system, you’ll probably be able to do this without any problems. Idea #2: I could visit some other stores and find a truly flicker-free monitor, buy a dozen of them, test them for flicker (just because the display model doesn’t flicker doesn’t mean the ones I actually get won’t flicker), return the ones that flicker and re-sell the flicker-free ones to people on this forum for cost + shipping. Then the people who buy these monitors could then confirm whether they are usable for them or not. We could conduct the purchase through eBay so you’d be protected if something went wrong (I have a 100% positive rating on eBay). I plan to do this for myself anyway because I’ve been wanting a new monitor (I have a decade-old 22” monitor that’s been good for me but it’s not working as well as it once was and I’d like something a little larger). I’ve got tons of more details, ideas, theories, etc., but don’t want to overwhelm you with information. In short, is there anyone who is willing to help validate my findings? Here’s those three screen shots.

Help wanted to measure flicker and/or test a flicker-free monitor

GregAtkinson

I believe I have found a method to test computer monitors, TVs, phones, laptops, etc. for headache-inducing flicker using a powerful photodetector (Thorlabs PDA100A2) and oscilloscope. It can zoom 3000x, which I believe is way beyond what anyone on this forum has used. Hats off to @KM who had mentioned it in a previous post and also described how to build a DIY device that I’ve been using.

Like many on this forum, I have a handful of devices that work for me and a growing junkyard of devices that I thought would be usable but in fact give me headaches. So I set about looking at each of my screens using the Thorlabs photodetector to see if I could tell the difference between the screens that give me headaches and the screens that do not.

When I zoomed to 100x magnification, I was able to see significant differences in the amount of flicker between screens that bother me and screens that do not. I then went to Best Buy and spent about 3 hours wandering the store testing 100+ devices (phones, TVs, laptops, etc.) in search of truly flicker-free devices. I was able to find about five laptops/chromebooks, one iPad, zero TVs, zero phones, and zero computer monitors.

Let me try to boil it all down to three screen shots:

My trusty Dell 5567 laptop that I’ve been using for five years without symptoms. There is barely any flicker.
A used Dell 5567 that I bought a few weeks ago as a backup. I cloned the SSD drive, so everything should be the same. But this one gives me headaches within minutes. The flicker is clearly visible.
An example flicker-free device that I found at Best Buy, just to prove that such a thing exists. This happens to be a laptop that I went ahead and ordered but have not yet received.

I really want to get some more people involved in this as I think this testing could have a huge impact. I have two ideas, but I’m sure there are others I’m not thinking of.

Idea #1: If someone with a variety of good and bad devices is willing to repeat my experiment, I’m happy to loan you my equipment. It’s not terribly difficult, but there are some steps that must be followed precisely. If you’re good at things like setting up your home theater system, you’ll probably be able to do this without any problems.

Idea #2: I could visit some other stores and find a truly flicker-free monitor, buy a dozen of them, test them for flicker (just because the display model doesn’t flicker doesn’t mean the ones I actually get won’t flicker), return the ones that flicker and re-sell the flicker-free ones to people on this forum for cost + shipping. Then the people who buy these monitors could then confirm whether they are usable for them or not. We could conduct the purchase through eBay so you’d be protected if something went wrong (I have a 100% positive rating on eBay). I plan to do this for myself anyway because I’ve been wanting a new monitor (I have a decade-old 22” monitor that’s been good for me but it’s not working as well as it once was and I’d like something a little larger).

I’ve got tons of more details, ideas, theories, etc., but don’t want to overwhelm you with information.

In short, is there anyone who is willing to help validate my findings?

Here’s those three screen shots.

Garman

GregAtkinson I was able to find about five laptops/chromebooks, one iPad

Could you tell us which iPad model was flicker-free? Do you happen to know the installed iOS version as well?
I have been looking to upgrade my iPad for a few years and testing the model you identified as flicker-free might be worth a try.

AlanSmith

To understand if there is a difference between Dell 5567 laptops, you need to install the AIDA64 program and see the panel model. Then enter panel model on the panelook website.

GregAtkinson

AlanSmith That's helpful. Thank you. It turns out the two panels were made by different manufacturers. That's somewhat encouraging. It would be worse if two panels from the same manufacturer were bad.

AlanSmith

If the laptop does not have a flicker of 100% brightness, this does not mean that it will not appear if you (suddenly) do not decide to reduce the screen brightness below 50% (before going to bed). The brightness curve works very cunningly (especially on Apple phones with OLED screens).

HP 17-cp2033dx -> 1600x900 SVA (TN + Film) | 60Hz | NTSC 60% | 220 cd/m2

Dell Inspiron 15 5000 5567-1753 (i7-7500U + AMD M445) -> PWM no detected

AlanSmith

GregAtkinson Did you go to the store, but did not write models of (bad) laptops & monitors? You can make the table "do not buy / bad for the eyes". Chromebooks do not flicker (because they are 6-bit). Write links to BestBuy (good) Chromebooks for (good) people.

AgentX20

Please keep us posted on your testing and that laptop…

Lauda89

Interesting. I want to buy an oscilloscope too because at the moment I'm using the 27GR95QE-B (OLED 2K 240hz) as a monitor which, connected to the gaming PC (13700K+4070 W11 21H2) causes me migraines after an hour of use, while connected to the MBA 15" It doesn't give me migraine problems and I can work all day.
I would like to see if an oscilloscope can measure a tangible difference.

Lauda89

Lauda89 The result: https://ledstrain.org/d/2577-im-testing-as-many-macbooks-as-possible-here-are-the-results/66

GregAtkinson

AlanSmith I had thought about creating something similar to a product catalog where each device would have a screen shot of how much it flickers. Ideally each panel within each model would have its own screen shot.

But I figured I'd start with figuring out whether truly flicker-free screens do solve the problem. Next time I go to Best Buy I'll make a note of the ones that are truly flicker free.

GregAtkinson

AlanSmith I went back to Best Buy today. Here's a chomebook with the least flickering that I could find. I didn't do extensive testing, but it's something to maybe take a look at.: "HP Chromebook x360 14b-cb0033dx"

GregAtkinson

Well, I received the HP laptop but it flickers way more than the store model. Here's an example screen shot. The flicker varies based on the color displayed on the panel, but this is pretty representative (except that white doesn't flicker).

Best Buy won't let me get into Device Manager (not surprisingly), so I have no info on whether the panel of the store model has the same model number of the device I received.

This laptop does seem to give me a headache (my headaches often come on less suddenly than many others on this forum, so I don't always know the cause of my headaches). I may use it a bit more, but I'll likely return it.

At this point, I'm still on the hunt for an external monitor that doesn't flicker.

KM

I wonder what exactly we are seeing here and why its form differs so much between devices. Seeing that the oscilloscope is running in AC mode, the flicker percentage must be very small. I have seen similar 60 Hz oscillations with the BPW34 sensor, but until now I didn't think that they contributed to eye strain or headaches.
If it is a scan line, like expected, the screen's pixel density and perhaps the total time it takes for a scan line to run from top to bottom could have a great influence on how the waveform appears on the oscilloscope. The sensor's angle and distance to the screen may be equally important.

Another thing that I ask myself is if there are any other, higher frequencies. The waves seem like they could be carrying a higher frequency signal, though it may just be some electronic disturbances. Perhaps caused by the Thorlabs amplifier? Usually backlights do have another frequency.

GregAtkinson

KM I have a couple answers for you. I'll start with the percent of flickering.

Here's a waveform that varies between += 10mv AC (so a 20mv variance)

Here's the same waveform on DC that is right at 2v:

So the variance is very close to 1%.

GregAtkinson

KM Regarding the higher frequency signal, I am finding that (as you mentioned) most panels have two (or more) frequencies, one about 60 hz and one about 100,000 hz.

Here are two screenshots from two different devices. Both are set to 100x zoom and 20 us/div. So it's measuring the high frequency flicker from the backlight.

My device with the least amount of backlight flicker (to prove that it's possible to have a pretty flat waveform):

A device with some significant backlight flicker:

It's worth noting that I can use some CCFL monitors without headaches, and these monitors flicker quite a bit at about 100khz. So I don't think the backlight flicker bothers me. For now I'm on the hunt for devices that don't have any flicker, just to be safe.

GregAtkinson

KM I have found that for some screens, the 60 hz flicker comes from pixel inversion.

Here's a screen shot of my newly-arrived HP laptop using https://pixelinversion.com/ (disclaimer: I made this web site). When you locate the correct pixel inversion pattern you can clearly see the flickering with the naked eye and detect it using the Thorlabs photodetector on 100x zoom (actually, it's so bad you can see it at lower zooms as well but it's really hard to make out at 0x zoom).

So half the pixels are always flickering with the above pattern and the other half are flickering with the same pattern but offset by 16.6 ms (or something like that - my formula might be off by a bit). In theory, the two waveforms would cancel each other out, but because the waveforms are not perfectly symmetrical, the screen flickers.

Here's what the combined waveform actually looks like:

GregAtkinson

KM Last post for a bit…

I'm not sure if this is new to PicoScope 7, but in PicoScope 7 you can download the raw data. So I downloaded it to Excel and created this graph to show how pixel inversion causes flickering if the waveforms aren't perfectly symmetrical.

jen

GregAtkinson how pixel inversion causes flickering if the waveforms aren't perfectly symmetrical.

Thanks so much for sharing all of this!

I found the same thing with subpixel flicker asymmetry creating gross combined flicker patterns that can be detected with a meter measuring a larger screen area - data posted here: https://www.flickersense.org/testing-leds-and-screens

For me, assuming there isn’t much backlight flicker, it seems like my symptoms are worse when there’s more pixel flicker, especially when the flicker of the red, green and blue subpixels are different from each other.

I’m just skimming because I can barely look at screens anymore, so I might have missed it - does your system allow you to measure the flicker of subpixels of different colors separately? If so, have you noticed any correlation with symptoms if there’s more color-to-color flicker? For some screens that hurt me I couldn’t detect much flicker grossly with my flicker meter, but once I started quantitating the subpixel flicker with Photoshop luminosity quantitation of individual subpixels in microscope slow-motion video frames, the patterns for which screens and screen settings hurt me most started to make some sense. For example, Nightshift on my Apple devices has always been awful for causing my concussion-like symptoms and it has some extra green and a lot of extra blue subpixel flicker compared to red. When the subpixel colors flicker similarly it seems to be less harmful for me.

AlanSmith

On Dell U2711 (CCFL) 140W also do not see flicker. Good monitor

Children go to school with the Chromebooks. Red Eye mode is off.

GregAtkinson

Garman It was the 11 inch iPad Pro. I don't know the iOS version. A couple caveats:

The biggest caveat is there's really no way to tell whether the panel that you get will be the same as the one I tested. I haven't figured out how to solve that problem (any ideas are welcome).
I don't remember which colors I tested, so it's possible a more extensive test would turn up flickering for other colors. I believe the screen shot below was taken while the screen was displaying white. Often with pixel inversion there won't be any flicker for white but there will be for lighter colors (light blue, light gray, etc.).

AlanSmith

The problem is Direct LED backlight (on new IPS, OLED and AMOLED panels). Imagine that an hundreds of lasers shine right into your eyes. Until 2018, the Edge LED monitor backlight was hidden from view (on the sides) by a thick frame. Eyes do not hurt from "old" monitors with Edge LED backlight. LG's AH-IPS panel is "safe." Good "old" 10bit AHVA likes.

AlanSmith

Can protective glass (for phone / monitor or TV) help eyes when flickering Direct LED screen backlight? Who wants to check if the eyes will hurt less with and without protective glass?

smilem

AlanSmith

No I do not think so. I tried museum glass that is AR coated, but does change spectrum. Tried on laptop with screen Screen is FHD 15.6" AUO B156HAN09.0 - € 130,10

https://ledstrain.org/d/1772-acer-v3-571g-with-8bit-ips-screen-dithering-is-very-bad-why

Can't use it more then 15min, it has dithering ! No noticeable flicker measured with Radex Lupin.