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.

      jen 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?

      I found something fascinating on your site: "It turns out that on every screen I've tested, Nightshift works by flickering green subpixels somewhat more and flickering blue subpixels a lot more, thus reducing the average amount of green and blue light. The overall effect is to create much more color-to-color flicker, since the screen flickers between very red and somewhat more blue/green."

      I never knew why nightshift bothered me. I have lent my equipment to a friend, but I'll take a look when I get it back. I can isolate the red/green/blue subpixels using this page, which has all 256 shades of gray, red, green and blue.

      The subpixel flicker mentioned on your site is what's called pixel inversion. I created this site (https://pixelinversion.com) to help visually see this flickering without a microscope. I can detect the pixel inversion flickering with the Thorlabs PDA100A2 (which has a gain/zoom feature) but I was not able to detect it with my homemade photodetector.

      I see that a lot of your work has been on lightbulbs. I'm super-happy with some MaxLite bulbs that I bought that have a completely flat waveform. For testing lightbulbs with a photodetector, I've just bought a color lens filter kit so I can see the waveforms of the different colors. I'll test that as well when I get my equipment back.

          GregAtkinson Thanks for the suggestion of light bulbs! I'll have to try those.

          When detecting differences in the flicker of different color subpixels, for Nightshift, I measured the flicker of the different subpixels (using the microscope and slow-motion video) on a completely white (or sometimes gray) screen without Nightshift and then using the same white (or gray) screen, but with Nightshift turned on at its warmest. It's super labor-intensive to do this using the Photoshop histogram/luminosity function, but I was glad I did. Before doing this test, I could feel that Nightshift was doing something that badly hurt me, but before this test, I didn't have good evidence for why. It's dramatic how much more the green and especially blue subpixels are fligckering than the red supixels during Nightshift.

          I could also detect differences in the flicker of different color subpixels (without Nightshift) using other colors on the screen. To find dramatic examples to measure with the microscope (since microscope/video measurement Photoshop analysis so labor intensive and triggering of symptoms for me), first I measured flicker with a flicker meter of different colors when only a single R, G, or B value was nonzero, at many settings. Then I chose to make 2 of the R, G, or B values nonzero, choosing combinations of values that on their own gave different flicker meter readings. Then when I recorded slow-motion microscope videos, i could see and quantify differences in luminosity of differently colored subpixels as they flickered. I could also put camera color filters between the flicker meter and the screen to get readings for different colors (Tiffen Red25, Blue47, and Green58 filters were the most useful for me). However, the microscope slow-motion video measurements tended to show color-to-color flicker best because I could measure individual subpixels and didn't have the interference between differently-phased flicker patterns that obscures readings with the flicker meter. Different screens had different colors with the most dramatic color-to-color flicker. On the screen I use most, i can mostly limit the colors that are used. I immediately feel pain/pressure in my head if I have even a small part of the screen displaying something with high color-to-color flicker.

          I'll be interested to hear what you find out with your method!

              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

                  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 !" ???

                    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).

                      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.

                        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.

                          "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.

                            smilem

                            Acer V3-771G (2013) is flicker.

                            MVA panel / PWM 200Hz.

                            Checked through Radex Lupin.

                              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.)

                                  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.

                                  6 days later

                                  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

                                  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 replied to this.
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