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"#5 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: 1. My trusty Dell 5567 laptop that I’ve been using for five years without symptoms. There is barely any flicker. 2. 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. 3. 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](https://www.bestbuy.com/site/hp-17-3-hd-laptop-amd-ryzen-3-7320u-8gb-memory-256gb-ssd-natural-silver/6554443.p?skuId=6554443) 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. [upl-image-preview url=https://i.imgur.com/ObWFCnY.png] [upl-image-preview url=https://i.imgur.com/HMO8S30.png] [upl-image-preview url=https://i.imgur.com/cVSxMUD.png]

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. ](https://www.panelook.com/M133NWF4+R0_IVO_13.3_LCM_overview_30696.html) ![](https://i.ibb.co/LPkjrxn/image-png-b36c288657ab1dff845e7a0d89c7e85d.png)

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 (](https://www.notebookcheck.net/Dell-Inspiron-15-5000-5567-1753-Notebook-Review.194950.0.html)**[i7-7500U + AMD M445)](https://www.notebookcheck.net/Dell-Inspiron-15-5000-5567-1753-Notebook-Review.194950.0.html)** -> PWM no detected

@"AlanSmith"#p31750 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.

Please keep us posted on your testing and that laptop…

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.

@"GregAtkinson"#p31759 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.

@"AlanSmith"#p31797 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.

@"AlanSmith"#p31797 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" [upl-image-preview url=https://i.imgur.com/0gdvMLl.png]

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). [upl-image-preview url=https://i.imgur.com/75fYGpY.png] 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.

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.

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

photon78s

jen

Have you tried these lights? I have a couple of these "flicker free" bulbs but don't have the high end measurement setup of Greg's. So far they are ok eyestrain wise.

https://www.waveformlighting.com/flicker-free-led-lighting

jen

photon78s https://www.waveformlighting.com/flicker-free-led-lighting

Yes, I can use the Waveform Centric Home A19 bulbs when they're new, but they start to flicker badly and cause brain injury for me as they age. You can see my measurement of the flicker of these bulbs over time here:
https://www.flickersense.org/testing-leds-and-screens

I stopped using Waveform Centric Home bulbs at home and switched back to incandescents with low flicker, but we still use Waveform bulbs at a family member's home. I just test their flicker periodically with a meter now. I'm glad they're still working for you!

We also tried some of their commercial lights at my workplace, but they flickered and injured my brain even when they were new:
https://www.flickersense.org/testing-leds-and-screens-before-2023

photon78s

jen

Thank you for sharing and for that wealth of information that is your website. Not sure if this is some kind of bias, but I recently been testing some old incandescents and they seem more comfortable than the waveform products I have (a19 bulbs and their led strips). The led strips are 12 volt battery powered.

For pixel flicker recordings, I am considering upgrading from my samsung 240 fps phone camera to a sony a7s III (also 240 fps capable) or some similar camera with very good sensor noise performance to reduce the impact of video noise on the analysis. I also feel eyestrain just from doing measurements with the samsung phone itself as it uses PWM OLED screen.

smilem

I wonder what store reps said when you showed up with ghostbusters kind of gear, and "I want to test all your phones and screens in the store !" ???

GregAtkinson

smilem I wonder what store reps said when you showed up with ghostbusters kind of gear, and "I want to test all your phones and screens in the store !" ???

We had a nerd fest! It was pretty cool. About five of them stopped by one at a time and asked (in a nice way) what I was doing so I showed them the non-flicker of my own laptop and then the flicker of the monitor I happened to be testing at the time. A couple of them even asked to see me test a particular monitor. Even a couple customers got into the mix.

This was at Micro Center, which is kind of a nerdy place. (I use Nerd as a compliment, btw).

smilem

Please can you clarify you measuring methodology?

At what distance you measure from screen, what C mount lens you have attached that makes ZOOM possible?

The sensor PDA100A2 is uber expensive "at what it does". The Lupin old model (that cost 100Eur) without white diffuser measures really well up to 3000Hz sampling at 6000Hz and even outputs to android with 3 band peaks identified.

GregAtkinson

smilem I hold the device up directly to the screen. The device's housing blocks out all external light. The zoom/gain is a feature of the device. There are 8 gain settings that go from 0x all the way up to 3,000x.

I've had the old Lupin for quite a few years. I did not find it useful for testing screens. I found the DIY light detector described elsewhere on this forum to be quite a bit better. The Thorlabs PDA100A2 was $450, but worth every penny to me.

GregAtkinson

smilem BTW if you want a more detailed explanation, here's a how-to video I created a few weeks ago. My thinking has changed slightly since I created the video, but it's still 90% accurate.

https://youtu.be/AoJ2jFgpBik

smilem

"I've had the old Lupin for quite a few years. I did not find it useful for testing screens. I found the DIY light detector described elsewhere on this forum to be quite a bit better."

The Lupin can measure up to 3Khz, why you found it not good?

Why not use Thorlabs DET36A2 biased photodetector 124USD ? 11Mhz vs. 25Mhz for cheaper version is faster. Why not use OSRAM BPW34S PIN (cost 1.7Eur) photodiode up o 400Khz it works the same as Thorlabs DET36A2.

GregAtkinson

smilem The Lupin can measure up to 3Khz, why you found it not good?

Two things I didn't like about the Lupin. First, I like to see the actual graph, not just a flicker percentage. It's not just how much the light source is flickering, but how abrupt the light is flickering that affects me. For instance, incandescent bulbs flicker with 120hz, but they don't bother me. Second, maybe it was the 3Khz limit, but it wasn't reliable in detecting PWM.

smilem Why not use Thorlabs DET36A2 biased photodetector 124USD ? 11Mhz vs. 25Mhz for cheaper version is faster. Why not use OSRAM BPW34S PIN (cost 1.7Eur) photodiode up o 400Khz it works the same as Thorlabs DET36A2.

The big feature with the PDA100A2 is the switchable gain/zoom. For nearly all the graphs on this page, I'm using 100x zoom.

There may be cheaper alternatives. For instance, I know there's a 10x/100x gain amplifier on eBay for about $70. So maybe you could hook that up to the BPW34S and get good results. (In fact I bought it a few weeks ago, before I got the PDA100A2, and just never got around to using it.)

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.

AlanSmith

smilem

Acer V3-771G (2013) is flicker.

MVA panel / PWM 200Hz.

Checked through Radex Lupin.

GregAtkinson

FYI, I've been using the new monitor daily for the past three days for 4+ hours/day and it's great. No headaches. (I'm confident that I could put in full 8 or 12 hour days without headaches, but the nature of my life right now is that I'm not at my desk all day.)

Later this week I'll head to Micro Center and buy as many as I can (they say they have 12 in stock), test them for flicker, and let you know what I find. They are still on sale for $130 plus tax.

GregAtkinson

And of course by the time I got to Micro Center on Friday they were out of stock. So I'll check back daily until they're back in stock. (One of the staff said they should get them this week.)

Also, I counted the number of monitors on display and they actually have about 100. Some may be duplicates of the same model, but my point is that it's not easy to find a monitor with no flicker. Only 3 out of those 100 (one 27" and two 24") were flicker free/virtually no flicker.

qb74

You could also use Rtings' tests for monitor flicker, which is pretty reliable
https://www.rtings.com/monitor/tests/motion/image-flicker

GregAtkinson

qb74 You could also use Rtings' tests for monitor flicker, which is pretty reliable

My hypothesis is that I'm sensitive to very small amounts of flicker (too small to show up on the Rtings tests). I have a number of devices that are supposedly flicker-free that give me headaches.

jen

GregAtkinson qb74 I'm also sensitive to very low amounts of flicker. The screen flicker can be virtually nonexistent when measured grossly with a flicker meter. For me it seems that for screens lacking dramatic backlight flicker, my symptoms are worse with higher flicker of the individual subpixels that can be quite high and visible with a microscope and slow-motion video, but masked when measured collectively with a flicker meter so that it's virtually undetectable. And my symptoms are even worse when the pattern of subpixel flicker differs for the red, green, and blue groups of subpixels. I've also found that the pattern and magnitude of subpixel flicker varies widely for different colors and on different screens. Testing data and methodology here. Unfortunately, methods used currently on rtings or notebookcheck that only use some form of flicker meter/oscilloscope to grossly measure flicker of a relatively large screen area identify dramatic backlight flicker, but aren't able to detect what's happening with the subpixels and also generally aren't able to detect any color-to-color flicker. They should also be checking flicker when different colors are displayed. It's also true that even if only backlight flicker is considered, even extremely low flicker can cause brain injury for me, since some LED lights with less than 0.1% flicker cause injury for me.

GregAtkinson

qb74 You could also use Rtings' tests for monitor flicker, which is pretty reliable
https://www.rtings.com/monitor/tests/motion/image-flicker

Now that I look closer at the site, I shouldn't have dismissed it so quickly. If you really look at the waveform closely, you can see whether it flickers or not. Here's a good example that I took from their site that doesn't seem to flicker:

https://www.rtings.com/monitor/reviews/asus/rog-strix-xg27aq

I kinda got thrown off by the fact that nearly all of their monitors receive a rating of 10 for flicker (10 being the best). But if you ignore their numerical rating and look very closely for a perfectly flat, thin waveform, you could probably find a flicker-free monitor that way.

GregAtkinson

jen I've also found that the pattern and magnitude of subpixel flicker varies widely for different colors

I've noticed with pixel inversion that the light colors (light green, light red, light blue and combinations of those colors) often flicker more than darker colors or fully bright colors. I'm thinking it's probably technologically easier to be fully on or fully off, but the colors in the middle have more variation when switching polarity from positive to negative.

GregAtkinson

I bought 10 of the LG 27MQ450-B monitors today. I tested one today and it looks great.

White at 100x zoom (brightness 100%, contrast 40%)

#D0D0D0 at 100x zoom (brightness 100%, contrast 40%)

GregAtkinson

Here's the eBay listing for the ten monitors. I am charging the exact price I paid. Hopefully we can get 10 people to give it a shot. The only thing you have to lose is the cost of shipping both ways (and maybe some monitor-induced headaches). But on the upside you could get a usable monitor and help the community understand a bit more about what causes headaches and what doesn't.

https://www.ebay.com/itm/145603787681

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