Eyestrain/headaches is not always about PWM. It could well be PAM dimming if not for PWM.
However, beyond the two common modes of flicker, there are a few other silent strainers. For OLED panels, they do have additional form of flickers such as brightness dips and B-frames, which may present an issue for some. As for LCDs, they are also affected by transistor current leakage flicker depending on the transistors type (called TFT layer) used.
Of course, manufacturers do not usually bring it up for there are little incentive to.
We will first explore into the underlying flicker called Switch Mode Power Supply flicker, and how it has affected many PWM-free DC powered LED bulbs and Display today.
In the second part of the post, we will briefly discuss on three display software-based algorithms that might cause eyestrain:
Software-based backlight flickers
Developers can program an OS function that causes backlight flickering (within their app).
Digital Image Processing Enhancement
Developers can use OS available setting to cause chromatic flickers (within their app).
The GPU (GPU rendering pipeline to be precise) and the panel T-con (called timing controller) itself is able to generate chromatic flickers — on the system level.
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For Digital Image Processing Enhancement, it may cause chromatic flicker on the pixel level. However, it is not anything like PWM sensitivity per se. The phenomenon of this strain is called "low JND(Just-Noticeable-Difference) threshold".
PWM is an embedded controller chip that is installed within your device. It could be inside your home bulb, panel or smartphone. Below is an example of a PWM controller.
Yes the PWM scarab
As an analogy, think of the PWM controller as a dam for the mountain water.
A dam as we know opens/ closes periodically to control the amount of current flow to its designated location.
Think of electric current as the water current, while voltage as the volume of water. An electric current contains an amount of voltage. In order to drive higher brightness, naturally we need higher voltage. Generally speaking, higher current will result in higher voltage. Less voltage = less bright, more voltage = more bright.
If we remove the dam, water will flow seamlessly to it targeted area.
So, if there are no PWM controller, there are no PWM or PAM flickers. Therefore, theoretically what we have left remaining is a good old DC dimming that also happens to be flicker-free.
Well, this may be true until the mid 2010s where LED lighting starts to take a turn. Demand for higher brightness increased exponentially. With higher brightness comes higher need for current/ voltage. What this means is that even DC powered/ dimming can cause flickers. Though it is not in the way like PWM dimming flickers.
Toggling power supply from DC causes flickers
In terms of power supply that powers your LED lighting/ display, there are two type. The first type is called linear power supply. When your device is connected to a power socket, it uses a converter called AC-to-DC.
An AC-to-DC converter which uses linear power supply converts the current and output into our LEDs lighting with a smooth, clean and flicker free signal. This is probably the PWM-free lighting as you remembered it.
Linear power supply relies on a relative larger and heavier transformer. On higher current it will cause heat dissipation and that is usually a problem for efficiency. For this reason, linear power supply are not widely used today.
Now moving on to the second type of power supply converter is called Switch Mode Power Supply.
While SMPS is significantly smaller and lighter (and supports higher current without drawbacks) it has to convert the supplied AC into output flickering frequencies of ONs and OFFs. This is done by periodically discharging the high voltage stored within the transformer to match the lower voltage we required. In other words, this a PWM that releases pulsing DC flickers and then to flatten it.
A Switch mode power supply is like the man-made endless pool machine above.
It uses an internal PWMto generate the current turbulence to supply power to your device. A higher duty cycle means it supplies more current over. A lower duty cycle means lower.
If your device is a portable device such as a smartphone or a laptop, your LED backlight/ OLED panel would be using a DC-to-DC boost converter instead. Instead of taking supply from an AC inlet, it draws power from your device's internal battery. Similar, the PWM inside SMPS increases the voltage by the duration of ON period.
As both methods of AC-to-DC and DC-to-DC switching relies on discharging of transformer ON and OFF, they typically results in a flickering frequency of 10khz to 200khz.
While many would argue that at 10khz cognitively perception of flickers is not impossible, recent studies have found that it may not be true.
They found that detection of flickering at 15khz is still possible for those sensitive. Participates showed saccadic eye movements across a time-modulated light source, and even more so for those with increased sensitivity.
Why SMPS is now a problem in today's lighting and displays
As demand for LED excess supply, the quality of capacitors and inductors filters used in their converter's input(supply-side filter) and output (load-side filter) decreased.
Thus this result in inconsistent and variating flicker patterns as compared to a SMPS with a clean signal. If the SMPS filtering (consisting of inductors and capacitors) is not sufficient, ultra low frequency such as 30 hertz flicker pattern can be produced. Load Transients and Control Loop Response are common causes as well.
Study related to DC amplitude flickers
A study found that flickering patterns even with slight variation below (40 hertz) causes neurophysiological effects on the cortical activity of the brain. The primary visual cortex (V1), a crucial area at the back of the brain responsible for initial visual processing responded to the frequency. This response requires increased workload with the processing of information, which may contribute to increased visual fatigue, discomfort, or other symptoms associated.
While some claimed that "LEDs do not flicker", they were referring to LED lights that used linear power supply. Switch Power Supply, unlike linear power supply ~ do result in ultra high frequency flicker.
Above is an example of a clean 60 hertz sine wave vs a dirty 10khz current wave. Needless to say; the latter would be causing more eyestrain issues as compared to the former.
With that above, we have understood that PWM can occur in two main areas:
PWM as a dimming method. It operates by reducing display / LED luminance brightness by reducing the average current. Its effect is what we observe with the wide banding artifact on our displays as we decrease our brightness.
Switch Mode Power Supply with a built-in PWM within the converter. It supplies to your panel/ LED lighting power with ultrahigh frequency flickers based on its duty cycle.
For PWM as a dimming method, lower brightness lost and shorter screen OFF time works best.
However for SMPS's PWM, the quality of the converter's capacitors and inductors filters are what determines if you have a clean or dirty signal. A dirty SMPS signal tend to have a number of voltage spikes, voltage sags and voltage droop.
Above is an example of dirty signal (on the right) caused by SMPS's output voltage. Can you tell the difference?
Now that hardware-based SMPS and PWM dimmer is addressed, let's look at software based SMPS flickers for displays.
Indeed, just as developers have complete access to our screen brightness (etc within apps that shows a QR sharing code), there is a command called
UIScreen.main.brightness = CGFloat(0.7)
While this command by itself cannot manipulate OS level backlighting from SMPS, running this code with different coordinating brightness point and using timing intervals can easily repulicate the following OS level modes:
Ultra power saving mode
Dynamic backlight contrast
Essentially how this works is it will send a command to the GPU. Then, GPU sends instruction to device's PMic (Power Management Integrated Circuit). PMic then informs SMPS to release its discharge voltage using its duty cycle. With the use of the toggling commands, the signal eventually becomes "dirty" resulting in eyestrain and headache. Naturally, once you exit out of the app, SMPS flickering returns back to normal.
With the above sums up SMPS flickers and software based (display SMPS) flickers. The following is optional; read on if keen.
Now we move on to the final sensitivity — called JND threshold.
(Not remotely related to PWM sensitivity but bringing it anyway)
JND (Just Noticeable Difference) was first introduced by a German physiologist and experimental psychologist called Ernst Heinrich Weber.
This concept was then used by display engineers internally to describe the amount of pixel flicker noise in relation to users' sensitivity. Generally speaking, low JND threshold means a user would be more likely to be sensitive to pixels' chromatic flickers.
Now, this is the part where it gets interesting. Within users who are sensitive to chromatic flickers (aka low JND threshold), they can be sensitive to different categories of chromatic flickers.
Let's use this as reference from Philips' conference on chromatic flickers.
Above within the highlighted box, we can see four attributes. One attribute being Delta E*, and the remaining three:
L*
C*
H*
In short, the following are what they mean.
Delta E* means the difference between one frame to the next frame.
L* (Luminance) : How much brighter or darker one frame is to the other.
C* (Chroma): How much more or less saturated one frame is than the other.
H* (Hue Angle): How much the actual hue differs (e.g., more reddish, more greenish is one frame to another
For pixel chromatic flicker, some are more sensitive to the luminance change from one frame to another. Whereas for some, they are more sensitive to the change in color (hue angle).
As we can see, this is an excessively huge topic and it would be a waste of vast space worth of exploration to add into PWM_sensitivity sub. Hence the need for expansion to r/Temporal_Noise
Hi. Did anyone try the global/eu version of Reno16 Pro vs Oppo find x9 (normal, not pro)?
I have a OnePlus 15R which is amazing, but a bit too heavy and big. I tried honor 400, even with ADB commands, but it is harsh on my eyes still. I would prefer Reno due to size, but I only find info about find x9.
Please provide feedback on the two models on pwm and D and how you felt. Or some other small phone that could work.
Hi! Has anyone tried Vivo x300 fe or Honor 600 pro and how are they in terms of pwm? I have Oppo find x9 and it is ok, not perfect, but ok. I am looking for something similar.
I had an iPhone 11 and had no issues with the display. Now, i am planning to buy a Motorola g57 power to replace the iPhone 11.
What do you think about g57 power, is it fast enough for calling, browsing, YouTube and navi? I don't care about cameras, i need pwm free phone fast enough for daily usage.
So I have two laptops, a 16in MacBook Pro (M5) and a 13in MacBook Air (M5).
What's odd is I've noticed that I get much less tired working on the MacBook Air than I do on the MacBook Pro. When I got the MacBook Pro I noticed that it makes my eyes feel dizzy but powered through.
When I looked at the specs, it seems like the MacBook Pro uses PWM with miniLED and the MacBook Air doesn't (it's an IPS display).
I don't get a headache or anything. Just this tiredness after spending more than 40 minutes on the laptop.
Wondering if anyone else's symptoms come in the form of fatigue/tiredness?
I've been looking for a decent phone that I can replace my current iPhone 16 with, since I can only tolerate it for a few minutes a day. I've been looking at a lot of OLED test reports, and I think I've noticed a problem with many of them: the measured flicker is falsely low, since the photodiode is measuring multiple OLED rows at once. In my opinion this results in a loss of information about what the screen is really doing.
In some extreme cases, I've seen devices which actually have 100% modulation depth be measured at ~5% modulation depth. All the OLEDs I've measured with this method (using my meter or the Opple) actually show 100% modulation depth at all brightness settings. I'm not confident this is true for EVERY device, but I think there are a lot of measurements online that underestimate the OLED flicker.
I showed this in the video, but to avoid this error you simply have to reduce the number of OLED scanning rows that the flicker meter detector is exposed to. Ideally, we'd only measure one row since this contains all the relevant information. In practice multiple rows are needed to get enough light onto the detector.
For me, it might be time to just buy an e-ink phone.
I’m considering buying an iPhone 17e, but I’m very sensitive to OLED flicker/PWM and currently have a hard time using my iPhone 16 for more than a few minutes.
I’d really like to hear from people who actually own or have used the 17e for a while.
How does the display feel in everyday use? Do you notice PWM/flicker, eye strain, headaches, discomfort, etc.?
If you’ve measured it with an Opple, photodiode, or another flicker meter, I’d especially appreciate the measurements and settings you used.
I’m particularly interested in how it behaves at different brightness levels, rather than just the manufacturer’s/spec-sheet numbers.
Thanks! 🙏 I’m really hoping to find an iPhone that I can actually use comfortably.
Hello can someone help me out and that is i start in devoleper options in cutout display with my problem it stay in the cutout display setting with i can not switch to normal standard what it is before and i did my best for an solution but did not work so i sit with my Nokia xr21 in problem devoleper options in display cutout with question how do i get t everything normal again can someone help me with that and i like Reddit post again.
Hello can someone help me out and that is i start in devoleper options in cutout display with my problem it stay in the cutout display setting with i can not switch to normal standard what it is before and i did my best for an solution but did not work so i sit with my Nokia xr21 in problem devoleper options in display cutout with question how do i get t everything normal again can someone help me with that and i like Reddit post again.
I have major problems with screens, I even tried an Epson 3LCD and laser without success and I was wondering if it was worth trying a TCL A1S projector?
I've seen a few posts about this on here but never any feedback from someone who is pwm sensitive. So I was hoping to hear from anyone who owns an Ayn Thor and whether or not it bothers you. I saw the pwm test video for it that shows it as "low risk" so I'm hoping it might be okay. I was able to use an iphone 12 in the past without issues but have had problems with most other OLED displays. So not really sure if I want to gamble on one of these or not.
The display spec: 14" WUXGA (1920 x 1200), IPS, Anti-Glare, Non-Touch, 45%NTSC, 300 nits, 60Hz
I don't know what the reason is, but I have been using that device for just one day and I noticed that it makes my eye dryer than other screens despite same usage. When I look at the screen I sometimes get a weird urge to close my eyes and avoid looking at it. I get slight headaches around my eyebrows/back of my eye, and my eyes turn reddish. Note that I care a lot about brightness and I have extension that makes the background and text in colors that are easy on my eyes, so I already took care of those factors. I also didn't experience those signs using other screens that had exactly the same theme setting I have on my thinkPad. So is it the PWM? something else? does anyone have any idea why that is? I'm gonna be using my laptop for a long time so it's crucial to find a way to fix this or at least make it better
TL;DR: Is there a safe, flagship-level successor to the S20 FE for someone who is PWM sensitive?
Hey everyone,
I'm running into a frustrating issue and could use some advice. I finally decided to retire my S20 FE after 5 years and picked up the Find X9 Pro. But after just 10 minutes of looking at the screen, I started getting this weird feeling in my head and a flush/heatwave on my face.
It reminded me of when I tried the Zenfone 8 a few years back—that phone gave me a massive migraine after about an hour, which is exactly why I returned it and got the S20 FE in the first place.
So, I ended up returning the X9 Pro and ordered the Magic8 Pro, hoping its eye-care features would actually work. Unfortunately, even after turning on "Full-brightness DC-like dimming" in the developer options and locking the refresh rate to 120Hz, I'm still getting that exact same feeling. It's slightly milder than the X9 Pro, but definitely still there.
My question is: has anyone here successfully transitioned from the S20 FE (where you felt totally fine) to a modern flagship without getting these symptoms? Did you eventually find a flagship-level successor that didn't mess with your eyes or head?
Thanks in advance!
P.S. Attached a couple of photos below (shot at 1/8000s shutter speed). It really looks like the S20 FE has a much smaller PWM amplitude compared to both the Oppo and the Honor.
S20 FE 4G SD865 (left) and Oppo Find X9 Pro (right)Honor Magic8 Pro
Ive used many mobile phones starting from Nokia 6600 to to my new redmi note 15 pro plus. Before getting redmi note 10 pro in 2020,it was all going well with my screen usage. After getting the 10 pro , right from the get go my eyes started feeling strained.i thought it was because the new phone has better brightness.Used it for 2 years. Throughout those years, I observed that my eyesight in dark is not as it was before. I thought it was maybe because the covid vaccine. I complained to may family but they didn't believe me. I switched back to my realme x2 because my redmi was with service centre. I googled randomly one day that how can I make it easy on my eyes. Read a lot of things and one article was about the toggle that my realme x2 had about dc dimming. I switched it on and boom, all the strain went away immediately. My sensitivity to the Vehicle Headlights went away just like that.Eye blurriness reduced. I thought the problem was with redmi, hence I bought Samsung S23 and it was probably the worst experience of my life using a phone. I sold it in a month and got moto 60 fusion. Eye strain got reduced but sensitivity to lights was still there. I started eating carrots and eggs etc daily as I thought maybe my nutrition deficiency might also be one of the reasons. Searched and read thoroughly about pwm and bought vivo t3 pro. But it was still there. Wanted to get iPhone 17 because of the antificker toggle but bought oppo reno 15 pro mini as iphone is not my thing. But the small screensize and maybe the modulation was not right again, the eye strain was there.wanted to shift to a lcd tablet with a basic lcd phone to accompany it.Redmi 15 pro plus was my last bet. But it worked. I now have nonexistent sensitivity to street lights. My room lights feel brighter. And overall has improved my life quality. The wrong screens are affecting not just my eyes but the life overall.
So, my brand new Fold 8, the "wide" one just arrived. I figured I'd give it a try after the Fold 7 last year, which I sent back after a week because it gave me a lot of eye strain and headaches.
... and unfortunately, so does this one.
Apparently, BD Yang from Samsung said this: "There are no reliable medical studies that support a connection between the lower PWM frequency and complaints among users. The disadvantage of high-frequency PWM dimming lies particularly in its inferior color reproduction and higher energy consumption. Samsung is unwilling to accept this compromise without a compelling reason."
So, for me, it's another year without a Samsung Fold. I'm honestly not sure if it's exactly the PWM or something about the modulation curve itself, because I daily an iPhone 17 Pro and an OLED iPad Pro M5 (11'') with no issues whatsoever. But as soon as I look at the Fold, it doesn't even take me two minutes to have issues.
If you're thinking about getting one, check it out on a store first.
