Eyestrain triggers

Hello Nicholas!
I suppose you suspect some underlying neurological condition or influence? I cannot see the common ground here for all cases for now, so I am very careful with any conclusions. I also suspected that there should be something in common but now I think there might be only some parts of neurological influence in common. And even that is yet to prove.
So I would call those things sources, but not triggers. Jen, the scientist who created https://www.flickersense.org/ recently and is present here on forum, found data that visible 40Hz stroboscopic flicker leads to neuroinflammation in mice, for example. Again, it it yet to prove that invisible PWM flicker may lead to neuroinflammation in humans. There is another theory that in influences involuntary eye movements (saccades). If any of those theories turns out to be truth, PWM would be a separate source and not a trigger of an underlying condition.

With all that said, I do totally support this idea with complete list of sources and solutions. I've done that for Russian-speaking forum and here is the list of every known problem on smartphones for now:

1. PWM: stroboscopic invisible flicker
2. FRC/Temporal dithering/Inversion: small potentially slightly visible flicker
3. Undefined problem X: complaints for piercing white color, feeling of looking at a wielding, inability to set up a pleasant brightness (screen always feels too bright), pressure and pain in or around the eyes, inability to focus on the screen, inability to focus far after the screen exposure, red eyes with red blood vessels (may appear next morning).
4. (Questionable) Excessive blue light. There are some reports that reducing blue light helps, but sometimes not for 100%.

What is also important is that sensitivity to those sources is totally unrelated. A person can be sensitive solely to one of those. Sometimes to few.
I would add that we also need to add tests to the list. And put everything later to the Ledstrain Wiki.

I would also include this list of very basic things to check before everything else.
Basic issues with smartphones that can be fixed easily:

1. Minimal brightness is too high
   There are many applications that can apply a black filter to the screen and thus reduce the screen brightness below the minimal system brightness, for example: Screen Dimmer, Screen Filter, Darker.
2. Problems with auto brightness
   Try turning off auto brightness and adjusting it manually, or install a third-party application from the GooglePlay.
3. Dynamic brightness
   A more malevolent version of auto-brightness: a built-in brightness adjustment in the firmware that cannot be turned off in the settings. This is how it is implemented on Nova 5T, for example. Dynamic brightness is easy to spot, but difficult to remove. Try asking on the forum of your device, which system file is responsible for this and how to delete it. Deleting system files can lead to some problems and bugs.
4. Rough surface of anti-reflective film, bad protective film or glass
5. Improper lighting conditions and a lot of reflected light rays from a glossy screen surface
6. Wrong screen distance: too far, to close
7. Screen too large /screen too small
   If a large screen creates too much light for you, try moving it away and at the same time increasing the font / scale of the elements.
   If the screen is too small, then the eyes will strain, reading, especially if it has a very small font.
8. Using the screen in the darkness
   The same as with a minimal brightness: try software that apply a black filter to the screen and thus reduce the screen brightness below the system level, for example: Screen Dimmer, Screen Filter, Darker.
9. Incorrect brightness and color temperature setting
   A general rule of thumb for eye comfort is that white on the screen should look the same as white on a piece of paper in your lighting. Take a sheet of white paper, place it next to your phone and try to achieve:
   the same brightness of the sheet and the screen
   the same shade of the sheet and the screen, the color temperature of the screen and the ambient light must match
10. Small font size
    Adjust the font to a comfortable size, enable scaling of screen elements - the picture should be comfortable, your eyes should not strain when looking at small objects.

Mrak0020 bad protective film or glass

Great list, thanks!

About the bad screen protectors - can you give me a link to some good thread on the topic, or is it basically scattered over the forum? Also is there a way to check/guess whether my (glass) screen protector is the issue, without removing it first? My screen does look weird when I look at it with polarized sunglasses.

Edit: Also, what is the fix in such cases? (a) To use the phone without a protector, or (b) To use the phone with a special (Skinomi?) protector?

logixoul if you are here on ledstrain more than 10 minutes, it is not an issue for you. If you have troubles with more than one screen (one with a protector) - you may skip it.
Polarized sunglasses reveal polarization of your screen, it can be linear or circular, and circular can be with rainbow effect or without. It is normal to see those through polarized sunglasses. I do not know if polarization itself may be a problem, in that case you can try Seagull's idea with tracing paper or even some cheap plastic eyeglasses (simply check through polarized sunglasses if polarization remains visible trough them).
Screen protectors may be helpful, not problematic, just like TPU screen protectors in the thread you answered to.
Now, if you glued a protector above one screen and that one screen became unusable, yep, the solution is to take it off or replace. Sometimes also anti-spy screen protectors can worsen symptoms, they are polarizers with specific qualities.

There might be also a bad screen coating on monitor. Monitors have glossy, matte or half-matte coating. Sometimes glossy one create to many glares. More importantly, sometimes matte one makes image sort of blurry and dirty, because grains of matte screen coating are bigger than tiny image details or scatter that image and make it unclear. Usually people are aware of this as when they compare two screens one is problematic solely due to this coating. But this info could be also helpful for newcomers. Someone should create similar list for monitors. There would be also Vcom flickering, bad cables etc.

List of known problems, tests and solutions for smartphones

(Will be updated)
0. Poor image quality on a screen
No complaints of eye pain from poor image quality on mobile phones have been reported yet. It is worth mentioning, though. First of all, poor image quality may happen on inexpensive phones or smaller Chinese brands.
May be present on 1-2 screens. If you are concerned about pain on a large number of devices, this is hardly the reason.
The phones of the same model can have different LCD screens (different suppliers, panels, different factories etc.), and also there could be one screen of different quality. This primarily applies to phones made by smaller Chinese brands. Be careful when purchasing and try to check a particular phone by your own eyes in advance.
Examples: article about different screen suppliers for iPhone 13,
post about 7 same POCO X3 NFC with 7 different screens (in Russian),
two Honor 50 comparison with the same settings,
variation in the quality of polarizers in oppo and vivo

1. PWM: stroboscopic invisible flicker
Notice that there are two important numbers to measure: PWM frequency and PWM flicker ratio. Notebookcheck measures only frequency.
A nice article about PWM and its influence, google translation from Russian
A simplified guide on how to test whether PWM affects you
Video that illustrates a pencil test, also called a pen test
Notebookcheck PWM frequency data table for all devices starting from 2016-2017
Phones can have dc-dimming option to reduce PWM. Try turning it on.
For Android phones there are few apps that can successfully eliminate PWM by setting up 100% brightness and applying a black filter above screen image, imitating dc-dimming:

• Oled Saver, probably uses complicated filter
• PWMfree, uses black filter

If your phone has dc-dimming, you still can use Oled Saver or another app together with dc-dimming. Dc-dimming on phones is not a remedy. Oled Saver can improve the situation further.

2. FRC/Temporal dithering/Inversion: small potentially slightly visible flicker
Jen's page with all the flicker descriptions in brief
Inversion tests (LCD only): http://www.techmind.org/lcd/index.html#inversion, http://www.lagom.nl/lcd-test/inversion.php
For now, there are no solutions to deal with these problems on smartphones, other than changing models or OS versions. For more details on each, see the list of problems for monitors.

3. Undefined problem X
Complaints for piercing white color, feeling of looking at a wielding, inability to set up a pleasant brightness (screen always feels too bright), pressure and pain in or around the eyes, inability to focus on the screen, inability to focus far after the screen exposure, red eyes with red blood vessels (may appear next morning). Those symptoms alone are not enough to differentiate this problem from other sources. It is better to check sensitivity to other sources before coming to conclusion that you have problem X.
If you have problem X, it is important to know the following: the problem has spread within phones since about 2017 (Xiaomi since 2016). No safe models have been found yet. If you have an old safe device, do not rush to sell it / throw it away. Try not to break it. When replacing the broken screen or when purchasing that same old model, you may encounter problem X again: there's no guarantee that old screen and new screen will be the same screen.
Problem was present before 2016, but rarely.
A very detailed post about problem
Can be related to screen parts: hypothesis here

4. Excessive blue light
There are some reports that reducing blue light helps, but sometimes not for 100%.
Many phones have a built-in blue filter, if not, you can download the application, there are a lot of apps on a search request "blue filter")
To check the influence of the blue color from the blue subpixel, you can read / look at a picture where there is no blue color: for example, set the background and font colors with the rgb code in the FBReader reader (any value, any value, 0)
To limit the blue spectrum from the entire screen - optics have glasses with a blue blocking filter.
Post about blue light blocking glasses success

A simplified guide on how to test whether PWM affects you
(for smartphones)

.1. Make sure your phone has low frequency PWM, using a pencil test. You can use your finger instead of a pencil.
Video that illustrates what you can see with a pencil test
Set your phone to your usual brightness level and go to a room where there are no flickering lamps. Wave your pencil in the air: you should see 2 pencils around the edges and between them there is a blurred, even trail of movement.
Now wave a pencil in front of the screen: if there is a low frequency PWM, you will see a lot of pencils instead of two. The lower the screen brightness, the stronger the PWM will be.
Check PWM on a white or light image on the screen. PWM may not be visible on dark images and there will be no PWM on black image.
If you didn't see the PWM as a result of this experiment, but your phone uses PWM to adjusts the brightness or other purposes, then its flickering is too frequent for most human eyes. According to IEEE 1789-2015, frequencies above 400 Hz are safe for most people.
Your eyes may be hypersensitive, but without special equipment it would be hard to check the PWM level that is right for you.

.2. Remove the PWM on your phone (this step can be done only on Android)

2.1. PWM is either absent at 100% brightness on most phone models, or becomes imperceptible. Set it to 100% brightness and see if it becomes easier for you. In order not to burden the eyes with brightness, for the purity of the experiment, conduct it in a well-lit place or on the street.
If it helps you, the cause of your problem is PWM.

2.2. Turn on dc dimming on your phone. Or remove PWM using Oled Saver or any other program that mimics dc dimming. It works like this: at 100% brightness, the program applies a black filter to the image to get the visual brightness of the screen you need. The picture quality will drop, but the picture will be created without the help of PWM technology.
After turning on the Oled Saver, do a pencil test to make sure the PWM is gone.
If it helped you and there is no pain in the eyes, the cause of the problem is PWM.

If it became easier for you, but partially, it can indicate that besides PWM, something else is bothering you.
Or you are facing with a response to high-frequency PWM and you need additional equipment to measure it.
If there is no difference, the cause of your pain is not PWM.

.3. Test phones without PWM
Important: in this experiment, you are changing not one parameter - PWM, but a whole bunch of parameters. You pick up another phone, which may have hundreds of differences from your phone.
Therefore, you will not be able to pinpoint the exact cause of the pain or eye strain.

Use noteboockcheck.net, where there is a table of PWM measurements for all phones. Notice, that measurements are available not for every phone, only for models starting from 2016-2017. Select models for the test. These can be phones with an IPS screen, or phones with OLED (Amoled, Super Amoled ec.) screen with a PWM frequency of 500 and higher. It is advisable to look at least at 5-6 different phones in order to narrow the range of causes of your pain. Two IPS phones from different years and manufacturers can be as different as night and day. If you only test one IPS phone, you might come up with a wrong conclusion.
Watch phones in dim lighting.

If it helps, PWM may be the cause of your pain. Or it may not be, testing different phones is not enough to pinpoint exact source with 100% probability.

Vision info

Binocular vision
It seems that in many cases bad tech triggers binocular vision problems.
It doesn't matter if you ever had any binocular vision problems or if your vision is perfect. Bad tech (or bad lighting) may interact with binocular vision, either causing additional troubles to people who have underlying problems or casing troubles to people who have perfect vision.
A very simple binocular vision self-test is a Brock string test. You can test yourself before an eyestrain and in the middle of it to understand what's going on. Brock string can also be a basic exercise.

If you suspect some underlying binocular vision problems you may consult with an optometrist and try:

• patching one eye (thread: One-Eye-Success for 10+ users on LEDStrain)
• exercises (you can learn some exercises at Martin's website about heterophoria)
• prism lenses (also discussed in thread: One-Eye-Success for 10+ users on LEDStrain. One example here)

Helpful links:

• Binocular vision troubles thread
• Wikipedia: Vergence and vergence dysfuncton
• Wikipedia: Binocular vision disorders
• Martin's website about heterophoria, created by one of Ledstrain members
• Martin's thread about progress
• Article about Binocular Vision Dysfunction
• Article that explains Binocular Vision Dysfunction and lens. Notice it is not a medical article and may contain mistakes
• Cover Test for Binocular Vision Dysfunction

If your core problem is bad tech and not an underlying condition, they can help you only partially (or not help at all). Patching one eye has the best chance to lessen tech influence.

Exercises and lens are not a cure if you never had any binocular vision problems. In that case, you better avoid bad tech and track your health with the Brock string test. You also can do exercises to help you get rid of symptoms faster, but be careful. Avoid overdoing them and avoid doing any exercises through pain, in some cases, it can make things worse: the bad screen will overwork your eye muscles and exercises/lens can overwork them additionally (example).

Please note that tech can affect your light sensitivity, lead to red eyes, etc. Track your eye health during exercises and patching. If you notice that your eyes or one open eye have increased light sensitivity, a lot of new visible blood vessels on the conjunctiva, or signs of inflammation (post with example), consider avoiding the bad screen.

Just to double-check: check your prescription glasses
If you wear prescription glasses/contacts and you have troubles not only with some screens but also with different activities that involve focusing, double-check your prescription.
Sometimes a mistake as little as 0.25 can lead to a lot of troubles: thread

List of image, signal, source, flicker related problems for monitors and laptops

1. PWM
Severe stroboscopic full-screen flicker, typically invisible (but easily detectable)
Article about PWM on notebookcheck
Iris - software that emulates DC dimming, equalling PWM to that is used for 100% brightness on your device
An old and experimental tool to adjust PWM driver frequency on Windows
IEEE Std 1789-2015 - recommended practices for PWM (pdf)

2. Vcom (LCD screens)
Small flickering of separate pixels, visible with bad factory settings
Article about Vcom
Post about Vcom on IXBT with flicker sample (Russian)

3. Inversion (LCD screens)
Small flickering of separate pixels, visible on test images
Inversion tests (should be displayed without any scaling in browser or OS, 1:1 ratio):
http://www.techmind.org/lcd/index.html#inversion
http://www.lagom.nl/lcd-test/inversion.php
Post about inversion leading to real life visible patterns
Post about inversion leading to real life visible colored spots (Russian)

4. Temporal dithering
Small flickering of pixels to create a color, potentially visible
Article about dithering with link to example (Caution! Severe flicker!)
More detailed article with examples
Another article that has advice on where to find dithering setting for Nvidia and AMD
Guide how to check whether dithering is affecting you and turn it off on Intel video cards (Russian)
Solution for temporal dithering from si_edgey
Post with a hardware and software setup to overcome dithering
Disabling dithering on Linux with Nvidia
On laptops, discrete GPU passes its output to the integrated GPU, so it has the final say on dithering or processing
Ditherig, software to turn off dithering: home page
Ditherig source code
You can find more about how to disable dithering through the forum search.
Dithering tests and capture:
By Seagull I have bought a capture card
By Seagull GPU dithering (Important findings: dithering frequency depends on the color and also dithering may disappear on some output modes of specific GPU)
By andc Screens under microscope in slowmo (dithering / FRC tests)
By ShivaWind Video of undefined dithering-like flicker, made visible with e-ink (scroll through user posts for more info)

5. FRC
Small flickering of pixels to create a color, potentially visible
It is a form of temporal dithering that is tied to the matrix and is used to increase matrix color capacity.
Data about many matrices can be found here:
http://www.tftcentral.…onitor_panel_parts.htm
http://www.panelook.com/modelsearch.php?op=size
How to check panel manufacturer on MacBook

6. Cables
Can create noise or artifacts on image. Also connection port can affect how a GPU will process a signal.
HDMA cable
Post about symptoms from a specific HDMI cable
Visible flicker from a malfunctioning HDMI cable (Russian) - this post was originally on ledstrain but I can't find the original one
Post about HDMI cable influence on eyestrain (Russian)
VGA cable
Post about VGA cable flicker
Conversion cables
Post about yellow tint with conversion cables

7. Image output
Post where eyestrain decreases with 16-235 range
Two examples of eyestrain or discomfort from different color range settings (Russian)
Post where 16-235 helped to eliminate eyestrain completely
Article about 16-235 and 0-255 (Russian)
Nvidia drivers automatically interpret monitor as TV when it is plugged in through HDMI and gives it 16-235 range (dated 2015) (Russian)
Image output and dithering:
GPU dithering (Important findings: dithering may be absent with some image output modes)

8. Image resolution scaling
Scaling algorithms make an image blurry
A big and very detailed article about scaling

9. Software and OS
Might be connected to dithering, color output, or other things that are hard to figure out
Detailed article about eyestrain from Linux (Russian)
Thread about eyestrain from linux, where disabling dithering does not fix the issue
Windows 10 anniversary edition (1607 and later) thread
Thread where rebooting Windows 10 in audit mode helped
Chrome thread

10. Visual effects in software
Chromatic aberration in games:
Thread about one game on Reddit
Few other visual effects in games
Factorio: headache and eye pain

11. Anti-aliasing, font smoothing
ClearType on Windows
Debian: https://ledstrain.org/…-rendering-eyestrain/8
Post about anti-aliasing influence on headaches, Ubuntu

Potential workarounds

E-ink and RLCD screens
Hisense thread
User who switched completely to e-ink (link to all his posts)
Some users report that using e-ink books causes discomfort even with the backlight turned off.

Projectors
Thread about successful experience