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

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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.

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2021 Award
Welcome to PF.
There is another explanation.
Maybe you stare at the screen and forget to blink.

russ_watters
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.

Staff Emeritus
Maybe this?

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.)

BillTre
Mentor
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?

russ_watters and BillTre
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.

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

russ_watters and BillTre
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.

Mentor
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

russ_watters and BillTre
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"
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.

BillTre
Staff Emeritus
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.

russ_watters, Motore and BillTre
Mentor
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
Gold Member
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.

Gold Member
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.

Mentor
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?

BillTre
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.

2021 Award
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
Mentor
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...

Homework Helper
berkeman
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).

Gold Member

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.

Staff Emeritus
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
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.

Staff Emeritus
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.

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