Please keep us posted on your testing and that laptop…
Help wanted to measure flicker and/or test a flicker-free monitor
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.
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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.
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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.
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"
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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.
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.
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%.
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.
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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 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.
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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.
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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.).
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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?
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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.
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.
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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.