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.

    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:

      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.

          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.

              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.

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

              1. 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).
              2. 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.).

                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?

                  KM By the way, here's a graph of ambient sunlight at 300x magnification (all the other graphs on this page are 100x). You can see that it's pretty flat, so the device isn't adding much noise.

                  Here it is at 100x magnification. Again, virtually no noise.

                    4 days later

                    I found a monitor today that has very low flicker. It's an LG 27MQ450-B. I paid $130.

                    My hypothesis, of course, is that I can use this monitor without headaches since the flicker is so low. It comes with a 30 day return policy, so I'll use it for a couple weeks and let you know what I think.

                    If it works well, I'll buy a handful of these, test them with my setup, and re-sell them at cost. Hopefully some of you will participate in this experiment.

                    Here are some screen shots. All screen shots are at 100x magnification.

                    Flicker at contrast setting of 40 and 100% brightness. This is the setting I plan to use

                    Same as above, except the contrast is set to 100. Interesting how the shape of the flicker changes with a higher contrast. This setting is roughly twice as bright as the previous setting.

                    Same as above, except the contrast is set to 0. This setting is about 1/3 as bright as when the contrast is set to 40. This is a bit too dim for me.

                    Also interesting: when I adjust the color settings, it changes the shape of the flicker. The default for this monitor is for R G and B to be at 50, but this screen shot has them all set to 100. Contrast is set to 40.

                      GregAtkinson definitely keep us updated! I need to find a safe monitor.. I'm worried polarization is also a factor for me.

                        GregAtkinson (1) So your eyes do not hurt from the flickering of pixels? And you can "safely" use the 6bit + FRC panel, right. (2) There are a lot of people with "photophobia" when their eyes hurt at 100% screen brightness. It is better to make tests at brightness close to zero. Radex Lupin (for $70) can do that. (3) The real 8bit AH-IPS monitor LG 27BK550Y-B has a PWM of 1% at brightness zero. Apple Cinema Display 27 (2011) is also safe for the eyes. Thank you.

                            Sony SDM-S205F S-IPS (2005).

                            100% brightness - > PWM 30%

                            The monitor burns out the eyes.

                            (in 2007, my eyes did not get tired)

                            Laptopmedia tests laptops from different manufacturers for flickering. Table rated (good/bad laptop). Even panel models. Why didn't I know about this site before? Add to Favorites.

                              AlanSmith I bought the radex lupin a few years ago. I found it helpful, but the the photodiode + oscilloscope was much more useful for me because I could see the shape of the graph, rather than just a percentage. For instance incandescent lights flicker, but it's a very smooth, gradual flicker (like a sine wave).

                              I do get headaches and tinnitus from the flickering of pixels, but I wouldn't say that my eyes hurt.

                              I can use a 6bit panel, but I generally use Intel integrated graphics which I don't think uses temporal dithering by default (I believe the default is spacial dithering, which doesn't bother me).

                              Bright screens bother me if they're excessively bright, but for me I don't need to turn the brightness all the way down to 0.

                                  AlanSmith The problem with Laptopmedia is they only test for PWM, and for me, PWM is only part of the problem.

                                    GregAtkinson I too also get tinnitus and headaches too from screens.

                                    Which model Intel graphics ? And what 6bit screen? I have heard this from someone else too! Very interesting

                                        GregAtkinson I found a monitor today that has very low flicker. It's an LG 27MQ450-B. I paid $130.

                                        My hypothesis, of course, is that I can use this monitor without headaches since the flicker is so low. It comes with a 30 day return policy, so I'll use it for a couple weeks and let you know what I think.

                                        While I appreciate your enthusiasm for this project there's something prudent I think you should know. Think I read somewhere that the vast majority of 1080p IPS panels are 6-bit+FRC (i.e use integrated dithering to achieve 8-bit color). You may be thinking "were there not good monitors in the past?". I think historically, 24" 1920x1200 IPS panels didn't use dithering and were often relegated for professional use, as opposed to a "consumer" product.

                                            JTL I read a couple places that this monitor supports 167 colors. I assume that means 167 out of a possible 256. So I assume it would dither (temporal and/or spatial) to get those 89 missing colors. Another site said it uses 8 bit + FRC.

                                            That said, my light meter can't detect any flicker caused by temporal dithering. I've tested 100+ shades of gray, red, green and blue. I'm not saying there isn't temporal dithering, but any decent* temporal dithering algorithm would be very difficult to detect with a light meter.

                                            Personally, I believe things like backlight flicker (not just PWM), OLED refresh cycles, pixel inversion and other pixel flicker are more likely to cause headaches because those things are detectable with a light meter. I don't think temporal dithering (or spatiotemporal dithering) will cause me headaches as long as it uses a decent algorithm. The flicker is so much smaller for temporal dithering than it is for those other causes of flicker.

                                            * I did use Ditherig to turn on temporal dithering for my laptop and on certain shades of gray the screen literally flickered from one shade to another and the flicker was visible (both with the naked eye and on my light meter). I'm assuming that most decent dithering algorithms use spatiotemporal dithering and are more intelligent about randomly spreading the use of adjacent colors through space and time.

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