Optical qualities of prism sheet and glass substrate (LCD screen)

[informerkh]

TL;DR Summary

Need help with defining optical qualities of two LCD screen layers that can severely hurt eyes when the screen is disassembled (what do they do to light to make it dangerous)

Hi! I am an electronics engineer and I would be very grateful for some help and suggestions with my problem. I am experiencing severe discomfort when working with almost any LCD screen (smartphones, laptops, monitors). Ophthalmologists say that I am completely healthy and they cannot understand why I experience pressing pain and painful or burning sensation in my eyes. It happens only when I am using an LCD screen. In my daily life I do not experience any slightest discomfort in my eyes. The problem is much more complicated than the most common causes of PWM flickering and blue light. I tested PWM and blue light and they have no impact to my problem. I also have a very old LCD monitor that is safe for me. I can't replace it with any other monitor, as I tried about 50 monitors (both new and old) and all of them hurt my eyes.

I experimented with monitors a lot, and came to the conclusion that the problem is optical. I completely disassembled the LCD screen, took a table lamp with an incandescent light bulb, applied all the screen layers above the lamp one by one, and directed a lamp light onto a white wall. I noticed that my eyes hurt when looking at two layers - a prismatic sheet and a lower glass substrate. Moreover, my eyes hurt even from the reflected light from the wall! The symptoms are exactly the same as when working with the monitor. Does anyone know what these two layers do to light and why it can hurt eyes? I have found many people who have the same problem, to a greater or lesser extent. I have not found any research other than the effect of PWM on flickering and blue light, so any information will be appreciated.

 

[Baluncore]

Welcome to PF.
There is another explanation.
Maybe you stare at the screen and forget to blink.

 

[informerkh]

Welcome to PF.
There is another explanation.
Maybe you stare at the screen and forget to blink.

Hello and thank you!
Symptoms start immediately, so there should be something else. This is also pretty obvious so I checked it at the very beginning.

 

[anorlunda]

Maybe this?
https://www.physicsforums.com/threads/ophthalmic-migraine.71816/

Maybe flicker?
https://www.physicsforums.com/threa...amp-result-in-flickering.933119/#post-5893420

That thread discusses the variability of people's sensitivity to flicker. Some people can perceive flicker at frequencies that most other people don't.

What about when you use an old fashioned CRT screen? (if you can find one.)

What about when you watch TV at home?

What about when you go to a movie theater? (If you can find one still open.)

 

[berkeman]

Welcome to PF. I moved this thread to our Biology/Medical forum, since the issue is most likely more biology-related versus Physics-related.

Summary:: Need help with defining optical qualities of two LCD screen layers that can severely hurt eyes when the screen is disassembled (what do they do to light to make it dangerous)

Ophthalmologists say that I am completely healthy and they cannot understand why I experience pressing pain and painful or burning sensation in my eyes. It happens only when I am using an LCD screen.

How many Ophthalmologists have you seen? What specific tests did they do to try to determine the source of your sensitivity?

 

[informerkh]

Welcome to PF. I moved this thread to our Biology/Medical forum, since the issue is most likely more biology-related versus Physics-related.
How many Ophthalmologists have you seen? What specific tests did they do to try to determine the source of your sensitivity?

Hello, thank you!
I replied to you in PM.
My problem has no connection to flickers and there were plenty of Ophthalmologists and flicker tests.

 

[berkeman]

Hello, thank you!
I replied to you in PM.

Please answer my question about the tests done by the doctors. Thank you.

 

[informerkh]

Thank you for the first suggestions but they are flicker and eye health related.
This is a 4th year of my struggles and moreover I am not alone. A plethora of people have similar problem without any ophthalmological problems found. So it is not only me doing tests, but a lot of other people.

I do not want to bring the discussion into the medical field as it brings no help.

Neither prism sheet nor glass substrate have an ability to flicker, they are just screen layers.

 

[informerkh]

Just wanted to add that under some conditions every person will feel pressure or discomfort or even pain: wearing someone else's glasses, looking at cross-view stereograms, looking at the tip of one's nose etc. It is obviously not a response to a flickering image of one's nose but a normal response to complicated accommodation conditions.
Probably light coming through these layers acquires some qualities that affect vision, focus or accommodation.
Glass substrate is not a simple layer of glass, it is covered by something that bends the laser ray: laser ray looks like big cross and not a small dot after coming through this layer. Prism film turns laser dot into a line.

 

[berkeman]

This is a 4th year of my struggles and moreover I am not alone. A plethora of people have similar problem without any ophthalmological problems found. So it is not only me doing tests, but a lot of other people.

If this is true, there must be some published studies on this problem. Are you sure nobody is studying it and publishing about it? What did your doctor(s) say when you asked them this question?

I do not want to bring the discussion into the medical field as it brings no help.

Well, so far from my perspective, it is most likely a medical issue. The LCD layers you are asking about don't change how the eye is stimulated AFAIK, and it seems like a waste of time to try to pursue that line of investigation.

Which of these tests did your doctors do?

https://medicine.uiowa.edu/eye/patient-care/clinics/neuro-ophthalmology/special-tests

And some other references:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3808926/

https://www.mayoclinic.org/diseases-conditions/optic-neuritis/diagnosis-treatment/drc-20354958

 

[informerkh]

If this is true, there must be some published studies on this problem. Are you sure nobody is studying it and publishing about it? What did your doctor(s) say when you asked them this question?

Unfortunately I found none. Doctors have no idea, one said she has other patients like this but have no idea about the cause. Some doctors who examined other people suggest binocular vision dysfunction and provided exercises, but BVD was so minor a questionable (compared to people with severe BVD and no screen complaints) and exercises bring no relief.

The layers you are asking about don't change how the eye is stimulated AFAIK

Prism layer is a lens that obviously bends the light, and another person said that looking at it clearly resembled looking at stereogram.

Again, as I said, discussion of medical conditions and medical tests here is very, very misleading. There is no problems with my peripheral vision, retina, neural path or flicker sensitivity. Neither can those layers flicker or add more light to my table lamp or affect my peripheral vision etc. They are just two unmoving pieces of material with some optical qualities.
Nothing among those medical tests also can't explain why some screens with absolutely same specs and absolutely same software are safe. Unless there are differences in the manufacturing.

 

[informerkh]

Tests for malingering in ophthalmology?
"manifestation of underlying psychopathology", "hysteria"

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3808926/

https://www.mayoclinic.org/diseases-conditions/optic-neuritis/diagnosis-treatment/drc-20354958

This is highly unpleasant and disrespectful.
The initial question covered solely optical qualities of two specific things. How this discussion proceeded makes no sense and no respect.

 

[anorlunda]

Have you tried working with the backlights of the LCD panels without the panels?

This is highly unpleasant and disrespectful.

That reaction is not appropriate. Everyone is subject to suggestion. I'm sure you have heard of the the placebo and nocebo effects? Psychopatholgy merely refers to those effects. There is nothing disrespectful about suggesting that any person can be affected by placebos/noceboes or by nurturing/hostile environments.

 

[berkeman]

I am experiencing severe discomfort when working with almost any LCD screen (smartphones, laptops, monitors). Ophthalmologists say that I am completely healthy and they cannot understand why I experience pressing pain and painful or burning sensation in my eyes. It happens only when I am using an LCD screen.

It was this pain that I was trying to address. That was the reason for listing the medical studies that I found with a fair amount of Google searching.

I also have a very old LCD monitor that is safe for me. I can't replace it with any other monitor, as I tried about 50 monitors (both new and old) and all of them hurt my eyes.

This may be an important key in your investigation. Since you are an EE, you might be able to figure out some sensors that help you to determine what are the differences between your old monitor and the newer ones that cause the pain. You can check both electrical noise, flicker depth and rates, and perhaps use some optical tests to see if the spectrum or divergence of the images are different.

 

[BillTre]

This is highly unpleasant and disrespectful.

You do realize that you are making a bunch of usual claims, but have provided no references for anything.
You are claiming everything else has been ruled out, and are dismissive of professionals, but do not explain why.

There are several possible alternative explanations which you dismiss, but don't explain why.

I could imagine possible neurological mechanisms for reactions to certain optical effects, but I don't know if its worth pursuing.

 

[informerkh]

This topic is discussed for years in communities like ledstrain.org and similar, in several languages, this is why. I came here for solely physical suggestions, not neurological. There are several screen problems that affect vision:
- PWM
- dithering/FRC
- this problem I came with
- blue light
They all are separate, because a person may react to PWM but not to FRC and vice versa. There are real people who are struggling with PWM and have immediate relief when PWM is 'turned off' (by dc-dimming or Oled Saver) at the very same screen. But there are almost no scientific researches about PWM, even though PWM is known for a pretty long time.
These layers I am talking about are way more new. And the problem itself became relevant to many people starting from 2016-2017, when something changed significantly in these particular LCD screen technologies. Also all the brands of mobile phones, where this particular problem is way stronger and affects the most people, were fighting last few years for max brightness and readability under the bright sun, and those particular tech is used for that purpose.

This is why I came strictly for physical suggestions and I have all the right to call 'hysteria' tag that was present via link another person posted as highly disrespectful both for me and for other people who share my problem.

 

[BillTre]

You are providing any links to anything supporting your claims.
It is your responsibility to provide those. I am not going to do your homework.
You are also using abbreviations I don't know and I am uninspired by you to look them up for you.

 

[informerkh]

You can check both electrical noise, flicker depth and rates, and perhaps use some optical tests to see if the spectrum or divergence of the images are different.

I've done all these tests. There's no difference. Moreover, I replaced the very LCD panel without any circuitry and backlight, put it into another comparable monitor, used it with the very same PC and drivers and the problem moved together with the LCD panel.
So I run out of ideas but I clearly see the same effect on those layers without any actual screen or image or flicker or spectrum etc.

 

[informerkh]

Have you tried working with the backlights of the LCD panels without the panels?

That reaction is not appropriate. Everyone is subject to suggestion. I'm sure you have heard of the the placebo and nocebo effects? Psychopatholgy merely refers to those effects. There is nothing disrespectful about suggesting that any person can be affected by placebos/noceboes or by nurturing/hostile environments.

Placebo have little to do with it, as that is easy to check. Placebo is the very first thing that is suggested by friends and family in these cases. But placebo can't make eyes bright red and lead to immediate appearance of red visible blood vessels on conjunctiva, but this thing can.

I replaced the very LCD panel, put it into a different monitor with a different backlight and problem clearly moved with the panel.

 

[berkeman]

I've done all these tests. There's no difference.

What is the part number of the old monitor that works for you? What screen resolution do you run it at? What screen resolution do you run the newer monitors at?

Do you wear contacts or glasses when using the computer LCD screen? Are they corrected for the distance to the screen?

 

[informerkh]

What is the part number of the old monitor that works for you?

Do you mind rephrasing it, please? English is not my first language and I am not sure if I understand the question.

What screen resolution do you run it at? What screen resolution do you run the newer monitors at?

Screen resolution had been also ruled out at the very beginning, there is no direct correlation neither for me nor for other people. Also there's no connection to ppi.

Do you wear contacts or glasses when using the computer LCD screen?

No, neither do the majority of people with this problem.

 

[informerkh]

What is the part number of the old monitor that works for you?

If you mean parts that are listed on the image at the first post, here is a full story about LCD replacement:
I had another safe monitor, but it is now partially broken and unusable. But I can still see a part of an image on the screen. I purchased a very same monitor model and it turned out to be unsafe. I did it 5 times and all the 5 screens were bad. I learned afterwards that this very device model had 20 different screen panels.
I placed good LCD panel without backlight and backlight unit (so everything from top to bottom polarizer) into a bad monitor and it became safe. It also had no prism layer at the very beginning and all the bad screens had it.
All the bad screens provided slightly different symptoms.

 

[Baluncore]

They are just two unmoving pieces of material with some optical qualities.

The optical properties of a layer will change significantly when a screen is delaminated. I doubt that a layer would have the same effect when assembled as it does when disassembled.

Have you tried looking at the screen through linear polarised sunglasses, or a circularly polarised anti-glare screen ?

 

[berkeman]

If you mean parts that are listed on the image at the first post, here is a full story about LCD replacement:

No, sorry if I wasn't clear. You said that you have an old LCD monitor that does not cause you the pain. I'm asking what make/model it is, like "Toshiba XYZ-56" or similar. And I'm asking what screen resolution you ran it at (1024x768 or smaller most likely), since older monitors would only be capable of limited resolution...

 

[hutchphd]

One thing you might try (depending upon what you are running) is to use white lettera on a dark background. Most desktops will offer that as a software switch; I have a friend who is a programmer and we used to use a special moniter cable to invert the stuff. Might help

https://www.eyeinfluence.org/post/d...e7SMbdxrSPCTsexRNDY-XgRDCsGgB0ShoCoMoQAvD_BwE

 

[informerkh]

I doubt that a layer would have the same effect when assembled as it does when disassembled.

Sure, it is possible. I think that if these layers lead to symptoms when disassembled, it might indicate a similarity of the cause. At the very least defining their optical qualities can help to find out what I am reacting to.

Have you tried looking at the screen through linear polarised sunglasses, or a circularly polarised anti-glare screen ?

Tried both linear and circular polarizers with no success. But I noticed that top polarizer have some influence. I removed it and replaced it with a polarizer from a good screen, and some part of burning sensation decreased. I found its patent later, it is a polarizer that improves image clarity and sharpness by making thin light rays (10-40% of the size of the subpixel).

 

[Tom.G]

After reading the thread a few things come to mind.

Does it help if the 'bad' screens are using only a single color (not White) and Black for display?

I am thinking the prisms may be redirecting the different colors in slightly different directions over the screen. This may cause your vision system to try to merge the colors into White depending on where they are on the screen. The different convergence across the screen may be overworking your vision system.

Another condition where this is a problem; some people have trouble looking at a fake 3D image using glasses with one Red lense and one Blue lens. (try a Google search for: anaglyph 3D)

Cheers,
Tom

 

[informerkh]

You said that you have an old LCD monitor that does not cause you the pain. I'm asking what make/model it is, like "Toshiba XYZ-56" or similar. And I'm asking what screen resolution you ran it at (1024x768 or smaller most likely), since older monitors would only be capable of limited resolution...

My safe monitor is LG l1717s, I am using it with the native resolution 1280*1024@60 Hz. All the other screes I also use with the native resolution.
And my less safe monitor is Eizo L985, it is way better than the others but still problematic. I am using it for 6 hours per day. Other screens are way worse.

I doubt there can be any connection to screen resolution. For example, people who have troubles with phone screens have them no matter what the ppi is. Someone can purchase a phone with higher ppi or with lower ppi and get the same pain as a resut.

 

[informerkh]

One thing you might try (depending upon what you are running) is to use white lettera on a dark background. Most desktops will offer that as a software switch; I have a friend who is a programmer and we used to use a special moniter cable to invert the stuff. Might help

https://www.eyeinfluence.org/post/d...e7SMbdxrSPCTsexRNDY-XgRDCsGgB0ShoCoMoQAvD_BwE

It seems that colors have little to do with it, I tried that and all the other people also tried. All modern phones have this feature as a software switch, and it doesn't help unfortunately.

 

[informerkh]

Does it help if the 'bad' screens are using only a single color (not White) and Black for display?

I am thinking the prisms may be redirecting the different colors in slightly different directions over the screen. This may cause your vision system to try to merge the colors into White depending on where they are on the screen. The different convergence across the screen may be overworking your vision system.

Another condition where this is a problem; some people have trouble looking at a fake 3D image using glasses with one Red lense and one Blue lens. (try a Google search for: anaglyph 3D)

Hello Tom, thank you for an interesting idea!
It doesn't help, and we also tried to check what happens if only one color is displayed. So if screen shows only pure red, green or blue RGB colors, with no text or other image, just one color, it still hurts (there's additional problem with displaying pure RGB with DCI-P3 screens, it requires more skill, but at least it was majorly one color).

But I feel that there should be something here... And I have this suspicion that something similar in light may be overworking vision system.
I haven't tried anaglyph yet.
I also can't understand what is special about this glass substrate, as it shouldn't be a lens. But it definitely bends laser light. It doesn't look like a lens. Maybe it has some sort of an anti-reflective coating. It reflects some part of a light and very slightly resembles a mirror.

There's also one experiment I've done: I removed the polarizers from a bad monitor and tried to look at a white screen (without polarizers, the screen is white with no image). The eye pressure, of course, was present, but I was surprised. Usually it took 5 minutes until the pain started, and when everything was white and bright and no image, it became so much easier for the eyes. I realized that my eyes were... they were like looking to nowhere. Then I took a black thread and hung it on top of the screen. And when I looked at this thread, the pain appeared in full force. And the eyes became like focused in the wrong place.

 

[anorlunda]

This account reminds me of software debugging. Tracking down the actual cause of these complaints can be very similar to finding a bug in software. Therefore, software debugging techniques may be useful.

Finding a bug in complex software can be a daunting detective task. The most common mistake in debugging methods is to prematurely jump to conclusions as to what causes can be excluded. That is why the ultimate solution is frequently to bring in a "fresh pair of eyes". The fresh person will not start with his/her brain contaminated with certainty about what the bug can not be. When the cause of an elusive bug is ultimately found, it is often the case that it is something that had earlier been excluded by the investigators.

There are parallels between software debugging and cold case murder investigative methods.

The most productive methodical way to track bugs is to begin with the collection of thorough and accurate records of how and when the symptoms appear. (Who remembers Jack Webb. "Just the facts madam. Nothing but the facts.") Any statement like "many people" hints that such record keeping has not yet occurred.

 

[informerkh]

This account reminds me of software debugging. Tracking down the actual cause of these complaints can be very similar to finding a bug in software.

You are totally correct!
Few month ago there appeared another person who was geeky enough to deal with this in a 'detective' way. She is probably less sensitive (her list of bad screens is smaller) but have a very severe reaction. I unfortunately can't share her research (actually I can, it is posted in this thread https://4pda.to/forum/index.php?showtopic=943228&st=0#entry111127837) because everything is written in Russian. GoogleTranslate makes text gibberish but if you want some details I can translate.
It is super detailed and covers probably whatever comes to your mind. Or I can ask her directly for more data. She also posted a few small details on ledstrain.org in English.
She had her first symptoms when purchased a new phone (Samsung Galaxy Note 10 lite, oled) this spring. She had symptoms on the second day. She sold it three weeks later and symptoms disappeared completely. Her safe screen was Samsung Galaxy Note 5 (also oled, very same SuperAmoled technology with PenTile). She used it with no symptoms for many years before and she used it with no symptoms up to this September. Phone died in September and she tried to replace it. She found out that she has same symptoms from every modern phone, both IPS and oled. She tried maybe 50. She have done a lot of tests since September.
I can translate other stories or post something from ledstain.org.

 

[informerkh]

What is interesting is that she also find that looking at those layers is problematic (eventually she disassembled one not so good but also not super bad screen). But it is early to jump to conclusions as she only just started her disassembling journey and she wants more screens to compare.

 

[anorlunda]

Reliable fact gathering can never be personal, and never collected by the persons involved. If there are many people with this complaint, and you are collectively ignored, then the only possibility may be to pool your money to hire a team of experienced investigators to do it the right way. Be prepared for a professional investigation to be very expensive. $1 million would not surprise me.

Perhaps more difficult, those putting up the money must accept the possibility that the evidence may point in a direction they consider offensive and insulting.

 

[informerkh]

Reliable fact gathering can never be personal, and never collected by the persons involved. If there are many people with this complaint, and you are collectively ignored, then the only possibility may be to pool your money to hire a team of experienced investigators to do it the right way. Be prepared for a professional investigation to be very expensive. $1 million would not surprise me.

That seems to be way expensive, I hope we can start from a cheaper way. Also it is hard to be this organized. People instead just purchase and sell 10-20-30 different monitors or phones or laptops.
And also this can't be done by any private investigators, only by a team of experienced engineers or researchers who are well versed in tech. And in optics. And in medicine.
I wonder why simply not discuss the initial question of this thread as it is the biggest cue right now.

I again have very unpleasant feeling that it is expected to proof that people have a real problem that has no severe underlying medical condition and is not a fake or mass placebo effect. I definitely came here not to investigate whether my pain is real or placebo, I sincerely hoped to discuss physics as it is called PhysicsForums
You may believe me or not, that is not the issue. I wonder what these two layers do and how exactly light passes through them, I tried to read the specs but they do not cover enough of details.
We can have a long discussion about medicine but then all the helpful physics discussion would be lost entirely.
Just for an example, when oled screens became common and people started complaining, it took a long time to define that they have eyestrain from a PWM that is used there extensively. Some people thought it is placebo or faking, and some thought that it is because lamps are directed into face or colors are too saturated etc. It was also hard to find cause PWM flicker is invisible to brain (but visible to eyes) and it made no damage that could be found by neuro ophthalmologists. Now this source of eyestrain is well-known, but there is still very limited scientific data about its influence.

 

[hutchphd]

I think it must be flicker related. This turns out to be rather involved for an LCD screen.
https://www.eetimes.com/lcd-screens-dont-flicker-or-do-they/
This can be simply investigated using an (amplified) photodiode and an oscilloscope. The frequencies are sub-kiloHz. You need some actual data.other than "my head hurts"!

 

[informerkh]

I think it must be flicker related. This turns out to be rather involved for an LCD screen.
https://www.eetimes.com/lcd-screens-dont-flicker-or-do-they/
This can be simply investigated using an (amplified) photodiode and an oscilloscope. The frequencies are sub-kiloHz. You need some actual data.other than "my head hurts"!

As I said it was investigated thoroughly.
Here is one example. I soldered a device that allows to smoothly change the PWM of the monitor in the range of 100Hz - 1200Hz. My sensitivity to PWM flicker is:
100-150Hz feels horrible
150-180Hz very bad
180-220Hz bad
220-240Hz OK
240-340Hz good
340-500Hz excellent
500-1000Hz makes no sense to use, no additional improvement
Also those layers from disassembled screen have no ability to flicker. I can take them in hands and... I do not know, wave fast? Then they will flicker

 

[hutchphd]

It is complicated. Please read the article. The amount of flicker depends upon lots of stuff.

 

[berkeman]

Here is one example. I soldered a device that allows to smoothly change the PWM of the monitor in the range of 100Hz - 1200Hz. My sensitivity to PWM flicker is:
100-150Hz feels horrible
150-180Hz very bad
180-220Hz bad
220-240Hz OK
240-340Hz good
340-500Hz excellent
500-1000Hz makes no sense to use, no additional improvement

Wait, that is very significant, no? If you can change the frequency of the flicker and it eliminates the pain, then the problem seems to be directly related to flicker frequency and not any of the LCD layers. Can you buy monitors with 340Hz refresh rates? What are typical LCD backlight flicker frequencies?

And I thought you said that your ophthalmologist(s) did flicker sensitivity tests on you and found nothing?

 

[informerkh]

Wait, that is very significant, no? If you can change the frequency of the flicker and it eliminates the pain, then the problem seems to be directly related to flicker frequency and not any of the LCD layers. Can you buy monitors with 340Hz refresh rates? What are typical LCD backlight flicker frequencies?

And I thought you said that your ophthalmologist(s) did flicker sensitivity tests on you and found nothing?

On the contrary, it shows that I am flicker sensitive only up to these frequencies, and none of my LCD screens have these flicker frequencies. These frequencies are typical not to LCD but to OLED screens (typical PWM frequencies) and many if not the most people are sensitive to these frequencies (I mean solely PWM frequencies).
Refresh rates are not PWM flicker (PWM is stroboscopic full-screen flicker) and they are way lower, but my safe refresh rate is 60 Hz like for the most people.

I said there were ophthalmological tests and flicker tests, not ophthalmological flicker tests

 

[jrmichler]

This can be simply investigated using an (amplified) photodiode and an oscilloscope. The frequencies are sub-kiloHz.

And, based on your flicker tests, a vote for this. It will tell what the screen is really doing, not what you think it is doing. Do this with screens that are both bad and good, or at least not as bad, looking for differences. If you do not find anything, try some color filters over the photodiode.

These type of problems are solvable. Finding the solution requires checking everything, especially those things that you don't think need to be checked.

It helps to create a document that states exactly what is known. The act of organizing that document frequently shows gaps in what is known. Those gaps need to be investigated. That document is useful in communicating what is known to people new to the problem. Such a document has helped me to solve similar difficult problems. It is well worth the time to create it.

 

[hutchphd]

I could not agree more and have had many similar experiences.

 

[informerkh]

And, based on your flicker tests, a vote for this. It will tell what the screen is really doing, not what you think it is doing. Do this with screens that are both bad and good, or at least not as bad, looking for differences. If you do not find anything, try some color filters over the photodiode.

These type of problems are solvable. Finding the solution requires checking everything, especially those things that you don't think need to be checked.

It helps to create a document that states exactly what is known. The act of organizing that document frequently shows gaps in what is known. Those gaps need to be investigated. That document is useful in communicating what is known to people new to the problem. Such a document has helped me to solve similar difficult problems. It is well worth the time to create it.

Sure, and this doc exists in Russian.
This is how we ruled out all the flicker influence (FRC, Vcom, inversion, PWM, refresh rate, software etc. etc.).
Again, I am now more interested in how exactly two non-flickering, very static pieces of material can be so problematic for the eyes.

 

[informerkh]

Ok, let me get this straight. Does anyone here have any experience with these layers or knows how they may work? I do realize that everyone are trying hard to help here and I am grateful, but maybe more experience with this particular tech is needed to help with this optical issue.

 

[berkeman]

Does anyone here have any experience with these layers or knows how they may work? I do realize that everyone are trying hard to help here and I am grateful, but maybe more experience with this particular tech is needed to help with this optical issue.

Sure, I can probably dig up some SID papers that discuss those layers (Society for Infomation Display -- the main technical society that deals with this sort of display technology).

Summary:: Need help with defining optical qualities of two LCD screen layers that can severely hurt eyes when the screen is disassembled (what do they do to light to make it dangerous)

I experimented with monitors a lot, and came to the conclusion that the problem is optical. I completely disassembled the LCD screen, took a table lamp with an incandescent light bulb, applied all the screen layers above the lamp one by one, and directed a lamp light onto a white wall. I noticed that my eyes hurt when looking at two layers - a prismatic sheet and a lower glass substrate. Moreover, my eyes hurt even from the reflected light from the wall! The symptoms are exactly the same as when working with the monitor. Does anyone know what these two layers do to light and why it can hurt eyes? I have found many people who have the same problem, to a greater or lesser extent. I have not found any research other than the effect of PWM on flickering and blue light, so any information will be appreciated.

So those two layers are the ones that you can shine DC illumination through and experience eye pain when looking at the light reflected from a white wall?

 

[informerkh]

Sure, I can probably dig up some SID papers that discuss those layers (Society for Infomation Display -- the main technical society that deals with this sort of display technology).

Wow! Thank you so much! That would be great! I sincerely hope that will help to figure things out! (At least to define set of non-flicker probable causes)

Yes, they are the prism sheet (it might be not a direct cause of pain in the monitor but it definitely unexplainably hurts when it is disassembled) and lower glass substrate (it has a thin film transistor layer on it and they cannot be separated, at least I could not separate them). Glass substrate might be a direct cause and I can't understand why it has effect so similar to a prism lens.

 

[Tom.G]

Here is one example. I soldered a device that allows to smoothly change the PWM of the monitor in the range of 100Hz - 1200Hz. My sensitivity to PWM flicker is:
100-150Hz feels horrible
150-180Hz very bad
180-220Hz bad
220-240Hz OK
240-340Hz good
340-500Hz excellent
500-1000Hz makes no sense to use, no additional improvement

Could you perhaps try lower frequencies for the flicker test?
I ask because common refresh rates are 60Hz and 75Hz, and your data shows greater trouble with lower frequencies.

Typical vision can detect 50Hz with averted vision, but it is not usually noticable when looking directly at the source. 120Hz is not typically visible under any condition. Maybe your eyes just have a faster response time than most! (I wonder if that's a survival advantage, either in the distant past, or in the present with powered vehicles to avoid. )

Also, your comments indicate that there is more than one contributing factor, specifically the refresh rate and the presence of the prismatic layer. You may find that there are other contributions.

Cheers,
Tom

 

[informerkh]

120Hz is not typically visible under any condition

There is a very simple explanation. There are two things participating in vision: eyes and brain. 120Hz is typically invisible to the brain. Person can't see it. But it is detected by eyes. Eyes can detect this flicker nonetheless. A very simple pen (or pencil) test proves this. If you take a pen and wave it in front of something that uses low frequency PWM (probably 120-400Hz, but here I am not sure) you will see not a usual pencil movement, very smooth, but a stroboscopic effect with 3, 5, 10 separate pencils. It is fun to watch. Meanwhile when looking at this source without any pencils you will see a usual normal image. This happens because brain takes an input from your eyes and proceeds it to you as a simple unmoving non-flickering image.

PWM is different than the refresh rate, it makes screen (or a light bulb) to flicker in a stroboscopic manner. So people are sensitive to it in a different way than to a refresh rate. No one knows yet why exactly people do react to PWM flicker. Does it break small involuntary eye movements (saccades) or does it affects the brain somehow or does it affects eyes in other way? Once scientists will find out.
But it is absolutely normal to react to PWM flicker. There is IEEE 1789-2015 - IEEE Recommended Practices for Modulating Current in High-Brightness LEDs for Mitigating Health Risks to Viewers. It says that frequencies up to 400 Hz are somewhat dangerous, they bring temporary health effects and should be avoided.
Here is the video that illustrated PWM flicker (it has a loud music so you might want to turn sound off):


I also tested another very common source of flicker, Vcom, and there is an opportunity to make it so strong that the flicker will be visible. I had no reaction to it. There are also test images for flickering, and my safe screens were flickering more that bad ones.
For example, this is how severe a Vcom flicker can be (upper image has Vcom flicker captured):

I would rather look at this flicker than to my bad non-flickering screen.

Yes, sure, there may be more than one contributing factor, hope to find them all!

 

[informerkh]

I just found this really cool article https://spectrum.ieee.org/visioncorrecting-display-means-no-need-for-reading-glasses. It describes methods of adjusting screen image for people who wear glasses so that they can see this image clearly without prescription glasses. I am now thinking again about that top polarizer with smaller than subpixel light rays. It may be possible to distort an image the other way round.
This is just a thought right now, nothing more.

 

[hutchphd]

I just found this really cool article about https://spectrum.ieee.org/visioncorrecting-display-means-no-need-for-reading-glasses.

I think this is not very newsworthy. In particular this technique has been known for a long time.

https://en.wikipedia.org/wiki/Pinhole_glasses

I don't see why you are so resistent to very good recommendations you have been given. I like to stumble around the internet sometimes but if the problem is related to flicker then why are you not looking at flicker using time resolved detection of some sort? Your methods are clearly inadequate to your purpose. What you say may be salient (or may not) but looking at the layers in a polarizing LCD stack is a very obtuse methodology for looking for frequency dependent effects.
I have no idea what the point of the video is other to illustrate one way to "see" frequencies higher than your flicker fusion rate. Folks with strobe lights know this.. that's why they have strobe lights.