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

[informerkh]

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.

Excuse me but I literally just described some tests for flicker sensitivity in detail.
Problem is not related to flicker.
Why do you suppose that it is?
I am not sensitive to any flickers other than the common low PWM rate that can easily be avoided and is not present in most LCD screens. Many LCD screens have no PWM at all!
I wrote here twice that replaced the LCD panel without the circuitry and problem moved with it. LCD panel cannot flicker by itself, it needs software of backlight or circuitry.

 

[berkeman]

Problem is not related to flicker.

Well, part of the problem might be, but you said that you can experience the pain with Static illumination through just the suspect LCD layers in isolation, right?

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]

Flicker is not part of the problem, I can easily test it and easily avoid it, it is a simple thing to check.
Right, that is exactly the case, I can experience the pain with static illumination. And that table lamp without LCD layers above it is completely fine for me, just like any ordinary lamp.
LCD panel without backlight layers, without backlight, with top polarizer replaced defines whether screen is good or bad for me. That is for sure. There's no other explanation why all the sensations from the screen move together with it. I placed it in another device and sensations moved with it. It is the most important cue.

 

[hutchphd]

I wrote here twice that replaced the LCD panel without the circuitry and problem moved with it. LCD panel cannot flicker by itself, it needs software of backlight or circuitry.

Did you read and understand the article I recommended??

 

[informerkh]

Did you read and understand the article I recommended??

You posted an article about a Vcom voltage. I posted just now! that I tested Vcom by adjusting it to make its flickering totally visible. Monitors (not all) have a resistor that can be twisted and made better / worse up to a pronounced flickering of neighboring subpixels that can be seen easily, just like on the picture I posted.

 

[berkeman]

Right, that is exactly the case, I can experience the pain with static illumination. And that table lamp without LCD layers above it is completely fine for me, just like any ordinary lamp.
LCD panel without backlight layers, without backlight, with top polarizer replaced defines whether screen is good or bad for me. That is for sure. There's no other explanation why all the sensations from the screen move together with it. I placed it in another device and sensations moved with it. It is the most important cue.

I agree that these are important clues.

Since you know others with similar eye pain problems with LCDs, do you know some who would be willing to go through a couple simple tests with you to start gathering more data?

If so, I'd suggest setting up a test where the subject is looking at a white wall in front of them, and from behind them, you randomly project the DC lamp light through different LCD layers to see if they have the same reactions that you do to the projected light on the wall. If they do (in this single-blind test), that could be pretty significant. (And to be complete, you should be one of the subjects in this test as well, with somebody else randomly switching out the layers.)

 

[informerkh]

Since you know others with similar eye pain problems with LCDs, do you know some who would be willing to go through a couple simple tests with you to start gathering more data?

If so, I'd suggest setting up a test where the subject is looking at a white wall in front of them, and from behind them, you randomly project the DC lamp light through different LCD layers to see if they have the same reactions that you do to the projected light on the wall. If they do (in this single-blind test), that could be pretty significant. (And to be complete, you should be one of the subjects in this test as well, with somebody else randomly switching out the layers.)

Yes, that is a great idea and I want to do something similar!
There are three problems with the execution:

1. People are scattered around the world and even within one country. As I need people who are willing to participate, have free time, have these layers... It is super hard to organize. And only two people are ready to disassemble screens right now, other simply do not have skill or waiting curiously for the results. But I hope things would improve.

2. Screen layers have to be found, so it should be exactly a bad screen, preferably the worst one for clear conclusions. Because of the next point in this list, the best thing to do is find some expensive modern smartphones with IPS screens and that takes some time and money (or less money and more time if service center can give some).

3. People have different sensitivity levels. I have high sensitivity but others have less. This problem is the most prominent on modern smartphones and most of them are OLEDs, so there's nothing to disassemble.

The lady I mentioned took the slightly bad IPS screen, disassembled it and found out that:
- she has way less problems with the exact same prism layer
- she has problems with a layer that comes above it, it is sort of another prism but probably multifunctional, we couldn't figure out its name. It looks very similar to prism film and may be some sort of reflective polarizer combined with prism film... I am not sure.
- she has pressing sensation that resembles phone when she takes lover glass substrate with transistors, that is glued with rear polarizer, and that undefined multifunctional layer together. She feels pressure when she applies them above the safe screen (with no image, just white background).

As I said, she is at the very beginning and she doesn't want to jump to conclusions.
This is a tricky problem and it affects people randomly, so there is no critical number of EEs to do all the tests yet. I hope it will change over time. Maybe if I have some clear findings or simple tests that everyone can do, there will be more data.

 

[Tom.G]

One more WAG (Wild Ass Guess):

Sensitivity to differential polarization. If you can get two polarizers (perhaps sacrifice a pair of plastic polarized sunglasses) to hold infront of your eyes.

Try viewing a screen thru the polarizers and see if you get any improvement/worsening when you independently rotate the polarizers. Try it with both 'good' and 'bad' screens.

Oh, and another WAG:
Do the screens give you a problem if you view them with only one eye?

Cheers,
Tom

 

[informerkh]

Hi Tom,
Those two ideas are also interesting!
I personally haven't tried polarizers independently yet, but I may try and see what happens. I asked the lady I mentioned (she uses nickname Mrak0020 on the forums I mentioned) and she also haven't tried. But both me and her tried different polarizers on top of bad screens, it changes nothing. I suppose polarization should not be differential if a screen is covered with a "good" polarizer above it.

I tried to look both eyes and one eye. Here what I've got: when I look with both eyes it hurts. When I look with one eye it also hurts. And what is interesting, it seems it still have some connection to accommodation or convergence despite it is one eye only. And here is why.
Mrak0020 also tried it and she also have more severe reaction (less sensitivity level, so less bad screens, but more severe reaction, her eyes hurt more). She has new visible red blood vessels in her eyes immediately after looking on a bad screen.
She was playing with stereograms and a simple test for binocular vision dysfunction: Brock string. Using those she understood that bad screen influences her convergence (it is the process of eye muscles rotating eyeballs so that they look to the same point), she had never any problems with it but after looking on the screen she can't focus far, eyes converge at the wrong point. That can be fixed with exercises for convergence, or looking on parallel-view stereograms. Looking on the bad screen influences her convergence immediately again, exercises do not prevent this. Screen does something to the eye rotation or focus.
Now when she looks with one eye only, most symptoms remain, and she sees those new visible blood vessels in the mirror on the surface of that one eye. So it is connected to binocular vision or eye muscles or eye focus, and a single eye exposure is somehow enough for the pain.
I haven't tried Brock string yet, we've met with Mrak0020 not so long ago.

 

[informerkh]

Just wanted to clarify if maybe something was misleading. I do not represent any organized group of people, and due to the different background, skills and countries it is hard to do anything organized. I've seen a number of similar stories and Mrak0020 spoke to different people with the same problem. They always are easy to recognize because people are not sensitive to flicker or ruled all the flickers out (it is not so hard to do, typical screen flickers can be measured or avoided and there are guides how to do it). People complain about the pressure, pain, inability to focus on image and weirdly "piercing colors" of the screen, especially white (no matter what the brightness is, it could be minimum brightness). Just like in this review of a monitor: https://libredd.it/r/Monitors/comments/pmmt2l/trying_to_reduce_eye_strain_and_headaches_from/
It is about a flicker-free monitor and it says "I still get bad eye-strain and headaches from looking at the monitor even just for a few minutes. It feels like the colors, especially the white color pierce through my eyes even at lowest brightness if that makes any sense." There are two similar reviews in Russian for the exact same model.
I also checked spectrum by simply replacing backlight and it changed nothing. And Mrak0020 tried about 50 different bad phones, they couldn't use absolutely same diodes. So it seems to be neither flicker nor spectrum related.

We've teamed up with Mrak0020 and we are eager to try different tests, that is the best we can do now.

 

[Tom.G]

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)

- 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?

Here are a couple Youtube videos on LCD displays. The first is a short quick look.



The second is about 34 minutes and the guy likes to talk but there is much information there. The prism layer is explained starting around 12 minutes. It is used for "light recycling," that is it redirects the backlight to go perpendicular thru the screen. Didn't you say that removing that layer reduced the discomfort?



Cheers,
Tom

 

[Vitina]

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.)

I agree with most of these studies...

As an old TV repairman, I recall that there was an on going balancing act between scan rate (29.5 fps US NTSC, 50 fps PAL Europe) and image retension of the phosphor.
Short retension ment flicker and retnal fatigue, long retension ment cometing of a moving object. Most opted for longer retention time.

Early computer monitors were monochrome and notorious for this.
LCD screens update on a pixle by pixle basis but used differing methods of maintaining and updating the image with florescent backlighting that operated from 120hz to 20khz somtimes creating a nausiating strobe effect.

Newer LCD screens have variable updates from 30fps to 240fps and a steady state led backlight. So the retension time can be very short and depending on subjet matter can affect people with "persistance of vision" problems.

I have this issue with some of these screens, early Apple CRT monitors were my biggest problem.
I have no problems with oled screens, no apearent or real flicker, no image shift due to thick LCD layers or shift in polarization, and no backlight.

 

[informerkh]

I have this issue with some of these screens, early Apple CRT monitors were my biggest problem.
I have no problems with oled screens, no apearent or real flicker, no image shift due to thick LCD layers or shift in polarization, and no backlight.

Hello, thank you for suggestions and happy holidays!

I doubt that this particular problem has any connection to this. For me, typical CRT frequencies of 75-85 Hz were difficult for perception, I saw how image 'pulses'. But my symptoms were completely different, my eyes were red and the head ached but I personally react to bad LCD in another way and clearly can differentiate my reaction. I was happy to purchase my first LCD and had zero problems with LCD screens for a long time.

CRT had only one drawback, flickering, although the picture felt more 'honest', like there was a 'surface' of the image, and LCD is the opposite - letters hang in the air (in the light) and there is no focus point for the eyes.

I didn’t think anyone’s eyes would hurt from the LCD, although now I found a bunch of similar complaints to mine, that started since LCD appeared and became widespread (early 2000s).

The problem I am fighting with right now is also present widely in modern oled screens.

I found a post (https://ledstrain.org/d/513-removing-the-metalic-semi-transparent-lcd-layer-helps) where the author removed a prism sheet from 5 different monitors and had a significant symptom decrease with every monitor. He said in the comments that nothing else helped. But he also said in another thread that LCD matrix itself is somehow problematic. It seems we came to the same conclusions.

 

[informerkh]

Here are a couple Youtube videos on LCD displays. The first is a short quick look.

The second is about 34 minutes and the guy likes to talk but there is much information there. The prism layer is explained starting around 12 minutes. It is used for "light recycling," that is it redirects the backlight to go perpendicular thru the screen. Didn't you say that removing that layer reduced the discomfort?

Cheers,
Tom

Hello Tom, happy holidays to you and have a great 2022!

I've seen a plethora of videos, including the first one, but the second one is new to me, it is way more detailed and interesting to watch. I found exact same 3M presentation that is featured in this video and yes, I told that removing this layer reduces the discomfort. Moreover, as I mentioned in another reply, I just found another person (https://ledstrain.org/d/513-removing-the-metalic-semi-transparent-lcd-layer-helps) who did exactly the same and reduced discomfort! He removed the prism layer from 5 monitors and got a significant relief, but he still could not find a way to use screen with no symptoms. He got stuck with the LCD matrix itself, he found it to be another cause of this problem. That corresponds with my experiences.
But LCD matrix is not a lens or at least should not be a lens, so it's hard to define what exactly happens.

I also wonder why prism layer that makes light go perpendicular trough the screen is problematic but any increase of brightness on the safe screen is completely OK for me. That is a big mystery to me.
I am not sure if all the light comes though it perpendicular, I've seen in some article that it reduces light angle but not completely.
I found a couple of articles about prism film and similar films (there can be few of them in one device):
http://archive.informationdisplay.o...play-marketplace-getting-the-light-through-tf
https://displaybly.com/brightness-enhancement-film-for-led-backlkight
And a big detailed part of a book (Applied Prismatic and Reflective Optics) that describes them (PDF file):
https://www.spiedigitallibrary.org/...sschapter&isFullBook=False&isResultClick=True
But I still can't figure out what's going on and how exactly this light is different from any other light. The most mysterious is LCD matrix (glass substrate with transistors) that should not be a lens.

 

[Tom.G]

Now if you could just find someone looking for a Masters Thesis subject, maybe you could talk them into researching the problem!

 

[berkeman]

Now if you could just find someone looking for a Masters Thesis subject, maybe you could talk them into researching the problem!

But the OP has still refused to conduct my single-blind experiment. That does not bode well for the future of this discucssion thread...

Yes, that is a great idea and I want to do something similar!
There are three problems with the execution:

1. People are scattered around the world and even within one country. As I need people who are willing to participate, have free time, have these layers... It is super hard to organize. And only two people are ready to disassemble screens right now, other simply do not have skill or waiting curiously for the results. But I hope things would improve.

2. Screen layers have to be found, so it should be exactly a bad screen, preferably the worst one for clear conclusions. Because of the next point in this list, the best thing to do is find some expensive modern smartphones with IPS screens and that takes some time and money (or less money and more time if service center can give some).

3. People have different sensitivity levels. I have high sensitivity but others have less. This problem is the most prominent on modern smartphones and most of them are OLEDs, so there's nothing to disassemble.

The lady I mentioned took the slightly bad IPS screen, disassembled it and found out that:
- she has way less problems with the exact same prism layer
- she has problems with a layer that comes above it, it is sort of another prism but probably multifunctional, we couldn't figure out its name. It looks very similar to prism film and may be some sort of reflective polarizer combined with prism film... I am not sure.
- she has pressing sensation that resembles phone when she takes lover glass substrate with transistors, that is glued with rear polarizer, and that undefined multifunctional layer together. She feels pressure when she applies them above the safe screen (with no image, just white background).

As I said, she is at the very beginning and she doesn't want to jump to conclusions.
This is a tricky problem and it affects people randomly, so there is no critical number of EEs to do all the tests yet. I hope it will change over time. Maybe if I have some clear findings or simple tests that everyone can do, there will be more data.

 

[russ_watters]

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

I just joined the thread (and we are discussing in the mods forum). A quick note for the overall problem (on PF and otherwise): if you want people to treat this/you like this is a real issue you need to take/treat it seriously. These flippant answers don't help your case. Surely with your education you must see that at face value what you are suggesting isn't possible, so if you need to be extra rigorous to show that it is real.

FYI, 3 or 4 years ago I had an issue that felt like someone stabbing me in the back of my eyes. It went on for months and an ophthalmologist found no issues. It was frustrating. I know the pain was real. And I was primed to reach for environmental issues. But reaching for answers in the minutiae of nothing is not useful.

 

[jrmichler]

But the OP has still refused to conduct my single-blind experiment.

When I see something like this, I start to wonder if the OP has a real problem, or is playing games with us. People with real problems are willing to check everything, even those things that appear to be obvious. People who are serious about solving a difficult problem will follow the advice given earlier about documentation, then show the document.

I suggest one more test. Modify a monitor so that the problem is minimized. Then have somebody else randomly switch between that monitor and a second monitor. Both monitors must be identical in appearance, the switching must be random, and the switching must be done out of your sight. The switching MUST be done such that you have no idea which monitor you are looking at. The test needs to be repeated several dozen times, and the result of each switch, or fake switch, recorded. And you must go into the test with an open mind.

 

[informerkh]

I clearly see I've come to a wrong place with the question. The majority have no actual experience with tech (or complicated optics) to make any advices, aside from very basic advices about how to organize data collection.

The blind test was proposed solely to prove to the contributors of this discussion that the problem is real and there are no tricks and no placebo. This very idea seems very odd to me, as on tech forums people usually are aware about eyestrains of different kinds and do not start from 'Prove it is real' or 'It is placebo'. Does a blind test make a slightest contribution to my research? No, as the problem is most definitely real for the everyone experiencing it (I provided a link to another person who tried the same experiment few years ago, but it was ignored, as I see). The only use of a blind test for me is to prove that the problem exists to hardware manufacturers, and that could be done when we know what to look for, what to test in every case.

The document in Russian (which as I said, was created long ago): https://4pda.to/forum/index.php?showtopic=943228&view=findpost&p=110571086

Now if you could just find someone looking for a Masters Thesis subject, maybe you could talk them into researching the problem!

Tom, if such a chance will appear, I will use it, but it seems that it requires more skills and time than a Master Thesis, we spend a lot of time already and there's still a long road ahead.
Your suggestions were interesting and valuable, thank you for your inputs!

Everyone else, sorry for the bother. I'll ask somewhere else.

 

[berkeman]

Whelp, we tried our best. Thanks everybody for trying to help the OP to alleviate his issues.

Thread is now closed.