All dimmers flicker the signal. A traditional dimmer switch uses a triac to flicker the AC current. But incandescent bulbs don't flicker (much) because they produce light by heating a wire until it glows (incandesces). So if the current flickers, then it just doesn't heat as much - producing the dimming effect.
That having been said, PWM-based brightness is entirely a function of the duty cycle. The frequency is almost irrelevant. If you drive an LED at a 50% duty cycle in order to get a particular brightness, you will have the same apparent brightness at 30 Hz, 120 Hz, 240 Hz or 10 MHz.
Which begs the question: what is the upper limit of photosensitivity? If flickering at 60 Hz is dangerous, what about 240 Hz? Or 20 kHz? Or 20 MHz? How high does the frequency have to be to avoid health issues or is it dangerous at all frequencies? Have there been any studies yet?
If a higher frequency will solve the problem, you don't need to drive your GPU at such a huge refresh rate. It should be possible to design a display with an internal frame buffer that can receive pixel data at the GPU's output frequency and flicker the LCD elements at a much higher frequency. I believe 240 Hz televisions do just that - they accept data at the usual 24, 25, 30, 50 or 60 Hz and refresh the pixels at 240 Hz.
All dimmers flicker the signal. A traditional dimmer switch uses a triac to flicker the AC current. But incandescent bulbs don't flicker (much) because they produce light by heating a wire until it glows (incandesces). So if the current flickers, then it just doesn't heat as much - producing the dimming effect.
That having been said, PWM-based brightness is entirely a function of the duty cycle. The frequency is almost irrelevant. If you drive an LED at a 50% duty cycle in order to get a particular brightness, you will have the same apparent brightness at 30 Hz, 120 Hz, 240 Hz or 10 MHz.
Which begs the question: what is the upper limit of photosensitivity? If flickering at 60 Hz is dangerous, what about 240 Hz? Or 20 kHz? Or 20 MHz? How high does the frequency have to be to avoid health issues or is it dangerous at all frequencies? Have there been any studies yet?
If a higher frequency will solve the problem, you don't need to drive your GPU at such a huge refresh rate. It should be possible to design a display with an internal frame buffer that can receive pixel data at the GPU's output frequency and flicker the LCD elements at a much higher frequency. I believe 240 Hz televisions do just that - they accept data at the usual 24, 25, 30, 50 or 60 Hz and refresh the pixels at 240 Hz.
While incandescent bulbs don't flicker much, they did have a little bit of flicker. Back in the old days of vinyl records, I had a cardboard circle I could place over the record label. The cardboard had a pattern printed on it that appeared to stand still when the record was spinning at the correct speed, and the pattern was illuminated by a light flickering at 120Hz. Under Fluorescent lights (which did flicker at completely on/off) the effect was easy to see. But even with incandescents, there was enough of a flicker that you adjust the speed.
In terms of flickering at a higher frequency than the frame rate, that's an old technique. Movie theaters used it for years. While movies had 24 frames per second, they would display each frame 2 or 3 times, to yield a flicker frequency of 48Hz or 72Hz.
The question here seems to be whether duty cycle is also an issue. In a quick web search, I didn't find any studies that suggested it was. I would be very interested in links to studies on the role of duty cycle.
One thing that does seem to be an issue, is how much of the field of view contains flickering. When watching TV, looking at a tablet/phone, or using a computer, the flickering is typically constrained to the screen. With the Apple Vision Pro, your entire filed of vision is a display. This is more like watching an immersive IMAX® movie, then looking at a computer monitor.
Apple doesn’t really care about your health. e.g. iMac can’t adjust the height of the display like many displays from Microsoft, Dell, LG and other brands. One height, your neck likes it or not. iPad is another example. I gave it up because tears ran out without control when I used it to read ebooks or emagazines not because of the contents but the vivid and over bright luminous LCD/LED. Wrists get chronic injury because of the weight and difficulty holding it. Don’t ask me to try the Vision Pro in a decade.
Apple doesn’t really care about your health. e.g. iMac can’t adjust the height of the display like many displays from Microsoft, Dell, LG and other brands. One height, your neck likes it or not. iPad is another example. I gave it up because tears ran out without control when I used it to read ebooks or emagazines not because of the contents but the vivid and over bright luminous LCD/LED. Wrists get chronic injury because of the weight and difficulty holding it. Don’t ask me to try the Vision Pro in a decade.
To be fair, the iPad has a brightness control. if the iPad is too bright for you, you can turn down the brightness.
In terms of weight, the iPad is about as heavy as a typical hardback book.
It seems, at least anecdotally, there is a difference with respect flicker and its tendency to cause irritation between the refresh rate of the panel (60, 120hz, etc) to produce motion effect and on/off flickering of the light source (PWM) to modulate brightness.
With the former, the light is source producing a set brightness, usually in the context of backlit LCD panel, is relatively constant and the pixels themselves are not emissive and change progressively in a top down or side to side pattern giving the illusion of motion to the user.
With the later, such as with PWM dimming, the light source itself is turning on and off and your brain is supposed to interpret that as either a dimmer or brighter screen. In the case of an OLED screen, the pixels are both the light source and the image source so the image itself is essential turning on and off repeatedly depending on the desired brightness. This seems to cause more eye strain for some people than how it was traditionally done with LCDs as described above.
Of course some LCD panels also use PWM backlights, but many do not. And ProMotion displays make it even more complicated with variable refresh rate.
Really pleased that this article has been written, the more exposure to this problem the better.
For all those stating you feel some pain or strain with the OLED screens etc but you're gonna give it a few weeks to see how it goes, please reconsider this.
I am almost three years with pain after an iphone 12pro gave me a headache, two weeks later I went back to my 11 and the pain started to subside, but the damage was done.
I have paid hundreds with a private neurologist who has diagnosed me with New Peristent Daily Headache(NPDH). The pain never goes, and never will. Usually brought on by viral infection but can be triggered but other means, repetitive eye strain being one. It triggers pain within glands in the brain.
I have tried lost of drugs, some which have been effective but the pain breaks through them after time. Next treatment once my current one fails is botox therapy, 37 injections in my scalp every 10 weeks.
Appreciate this PWM issue is only a very small percentage of users, and the chance of someone also getting my condition is even lower but if there is pain, please stop.
I would gladly use a Nokia 3310 for the rest of my life if it meant my condition went away.
Really pleased that this article has been written, the more exposure to this problem the better.
For all those stating you feel some pain or strain with the OLED screens etc but you're gonna give it a few weeks to see how it goes, please reconsider this.
I am almost three years with pain after an iphone 12pro gave me a headache, two weeks later I went back to my 11 and the pain started to subside, but the damage was done.
I have paid hundreds with a private neurologist who has diagnosed me with New Peristent Daily Headache(NPDH). The pain never goes, and never will. Usually brought on by viral infection but can be triggered but other means, repetitive eye strain being one. It triggers pain within glands in the brain.
I have tried lost of drugs, some which have been effective but the pain breaks through them after time. Next treatment once my current one fails is botox therapy, 37 injections in my scalp every 10 weeks.
Appreciate this PWM issue is only a very small percentage of users, and the chance of someone also getting my condition is even lower but if there is pain, please stop.
I would gladly use a Nokia 3310 for the rest of my life if it meant my condition went away.
I am sorry that you are going through this. You do bring up an interesting question. NPDH is normally brought on by a viral infection. How did your doctors determine whether your case was brought on by an OLED screen, or a viral infection that roughly coincided with you getting an OLED screen?
Human beings are biologically trained to assume cause and effect when two things happen at the same time. Often, there really is cause and effect, but sometimes it is just coincidence. Eat at a new restaurant and get sick the next day, and most people would conclude that the restaurant was the cause of the sickness, but it is also possible that the sickness was from some other cause, and it was just coincidental that you ate at a new restaurant.
When I was sick in bed with Covid, I ate a lot of cherry Lifesavers®. I ended up with a mild case and a full recovery. Should I conclude that the Lifesavers are a cure for Covid?
Really pleased that this article has been written, the more exposure to this problem the better.
For all those stating you feel some pain or strain with the OLED screens etc but you're gonna give it a few weeks to see how it goes, please reconsider this.
I am almost three years with pain after an iphone 12pro gave me a headache, two weeks later I went back to my 11 and the pain started to subside, but the damage was done.
I have paid hundreds with a private neurologist who has diagnosed me with New Peristent Daily Headache(NPDH). The pain never goes, and never will. Usually brought on by viral infection but can be triggered but other means, repetitive eye strain being one. It triggers pain within glands in the brain.
I have tried lost of drugs, some which have been effective but the pain breaks through them after time. Next treatment once my current one fails is botox therapy, 37 injections in my scalp every 10 weeks.
Appreciate this PWM issue is only a very small percentage of users, and the chance of someone also getting my condition is even lower but if there is pain, please stop.
I would gladly use a Nokia 3310 for the rest of my life if it meant my condition went away.
I am sorry that you are going through this. You do bring up an interesting question. NPDH is normally brought on by a viral infection. How did your doctors determine whether your case was brought on by an OLED screen, or a viral infection that roughly coincided with you getting an OLED screen?
Human beings are biologically trained to assume cause and effect when two things happen at the same time. Often, there really is cause and effect, but sometimes it is just coincidence. Eat at a new restaurant and get sick the next day, and most people would conclude that the restaurant was the cause of the sickness, but it is also possible that the sickness was from some other cause, and it was just coincidental that you ate at a new restaurant.
When I was sick in bed with Covid, I ate a lot of cherry Lifesavers®. I ended up with a mild case and a full recovery. Should I conclude that the Lifesavers are a cure for Covid?
I'm not certain why you're convinced that this isn't a real problem that can be induced by PWM. There are loads of studies in healthcare about it, and how it works -- which we've summarized accurately in this piece in conjunction with physicists, and neurologists. We've also discussed that it's rare, and who it's most impactful for.
I'm not sure what your agenda is, and you need to stop.
Really pleased that this article has been written, the more exposure to this problem the better.
For all those stating you feel some pain or strain with the OLED screens etc but you're gonna give it a few weeks to see how it goes, please reconsider this.
I am almost three years with pain after an iphone 12pro gave me a headache, two weeks later I went back to my 11 and the pain started to subside, but the damage was done.
I have paid hundreds with a private neurologist who has diagnosed me with New Peristent Daily Headache(NPDH). The pain never goes, and never will. Usually brought on by viral infection but can be triggered but other means, repetitive eye strain being one. It triggers pain within glands in the brain.
I have tried lost of drugs, some which have been effective but the pain breaks through them after time. Next treatment once my current one fails is botox therapy, 37 injections in my scalp every 10 weeks.
Appreciate this PWM issue is only a very small percentage of users, and the chance of someone also getting my condition is even lower but if there is pain, please stop.
I would gladly use a Nokia 3310 for the rest of my life if it meant my condition went away.
I am sorry that you are going through this. You do bring up an interesting question. NPDH is normally brought on by a viral infection. How did your doctors determine whether your case was brought on by an OLED screen, or a viral infection that roughly coincided with you getting an OLED screen?
Human beings are biologically trained to assume cause and effect when two things happen at the same time. Often, there really is cause and effect, but sometimes it is just coincidence. Eat at a new restaurant and get sick the next day, and most people would conclude that the restaurant was the cause of the sickness, but it is also possible that the sickness was from some other cause, and it was just coincidental that you ate at a new restaurant.
When I was sick in bed with Covid, I ate a lot of cherry Lifesavers®. I ended up with a mild case and a full recovery. Should I conclude that the Lifesavers are a cure for Covid?
I'm not certain why you're convinced that this isn't a real problem that can be induced by PWM. There are loads of studies in healthcare about it, and how it works -- which we've summarized accurately in this piece in conjunction with physicists, and neurologists. We've also discussed that it's rare, and who it's most impactful for.
I'm not sure what your agenda is, and you need to stop.
I don’t doubt that it’s real. I am genuinely curious as to how they differentiate a case caused by flicker vs a case caused by a virus. I would imagine that accurately diagnosing the cause is helpful in determining the best treatment.
Really pleased that this article has been written, the more exposure to this problem the better.
For all those stating you feel some pain or strain with the OLED screens etc but you're gonna give it a few weeks to see how it goes, please reconsider this.
I am almost three years with pain after an iphone 12pro gave me a headache, two weeks later I went back to my 11 and the pain started to subside, but the damage was done.
I have paid hundreds with a private neurologist who has diagnosed me with New Peristent Daily Headache(NPDH). The pain never goes, and never will. Usually brought on by viral infection but can be triggered but other means, repetitive eye strain being one. It triggers pain within glands in the brain.
I have tried lost of drugs, some which have been effective but the pain breaks through them after time. Next treatment once my current one fails is botox therapy, 37 injections in my scalp every 10 weeks.
Appreciate this PWM issue is only a very small percentage of users, and the chance of someone also getting my condition is even lower but if there is pain, please stop.
I would gladly use a Nokia 3310 for the rest of my life if it meant my condition went away.
I am sorry that you are going through this. You do bring up an interesting question. NPDH is normally brought on by a viral infection. How did your doctors determine whether your case was brought on by an OLED screen, or a viral infection that roughly coincided with you getting an OLED screen?
Human beings are biologically trained to assume cause and effect when two things happen at the same time. Often, there really is cause and effect, but sometimes it is just coincidence. Eat at a new restaurant and get sick the next day, and most people would conclude that the restaurant was the cause of the sickness, but it is also possible that the sickness was from some other cause, and it was just coincidental that you ate at a new restaurant.
When I was sick in bed with Covid, I ate a lot of cherry Lifesavers®. I ended up with a mild case and a full recovery. Should I conclude that the Lifesavers are a cure for Covid?
Some very random agenda you have there.
I am currently under the care of one of the best headache neurologists in UK, possibly the world. It’s seems you’ve googled my condition and diagnosed me.
My condition, as you say, can be brought on by a viral infection. However head traumas, surgery, exposure to certain elements such as strong fumes or bright flashes of light can also cause this. One of its characteristics is that you can pinpoint the exact time when it started, which for me, was the day I used my new phone.
It’s a fairly new condition but my neurologist and his team have noted an increase in recent years and the amount of screen time people have these days is probably not a coincidence.
My optician has so many more children wanting glasses from a younger age.
Theres a lot of folk who struggle with OLED but that number is about to shoot up once more and more use VR headsets with a screen so close to their eyes.
I just wish I had stopped with the phone and it not taken 2/3 weeks for my to realise that was the cause of my eye fatigue and headache.
I’m not some flat earther with uneducated beliefs. It’s science, and I’m happy that big hitters in the media world such as Apple Insider are starting to highlight the issues, hopefully more do the same which eventually forces Apple, Samsung etc to add options where PWM and OLED become safer.
Really pleased that this article has been written, the more exposure to this problem the better.
For all those stating you feel some pain or strain with the OLED screens etc but you're gonna give it a few weeks to see how it goes, please reconsider this.
I am almost three years with pain after an iphone 12pro gave me a headache, two weeks later I went back to my 11 and the pain started to subside, but the damage was done.
I have paid hundreds with a private neurologist who has diagnosed me with New Peristent Daily Headache(NPDH). The pain never goes, and never will. Usually brought on by viral infection but can be triggered but other means, repetitive eye strain being one. It triggers pain within glands in the brain.
I have tried lost of drugs, some which have been effective but the pain breaks through them after time. Next treatment once my current one fails is botox therapy, 37 injections in my scalp every 10 weeks.
Appreciate this PWM issue is only a very small percentage of users, and the chance of someone also getting my condition is even lower but if there is pain, please stop.
I would gladly use a Nokia 3310 for the rest of my life if it meant my condition went away.
I am sorry that you are going through this. You do bring up an interesting question. NPDH is normally brought on by a viral infection. How did your doctors determine whether your case was brought on by an OLED screen, or a viral infection that roughly coincided with you getting an OLED screen?
Human beings are biologically trained to assume cause and effect when two things happen at the same time. Often, there really is cause and effect, but sometimes it is just coincidence. Eat at a new restaurant and get sick the next day, and most people would conclude that the restaurant was the cause of the sickness, but it is also possible that the sickness was from some other cause, and it was just coincidental that you ate at a new restaurant.
When I was sick in bed with Covid, I ate a lot of cherry Lifesavers®. I ended up with a mild case and a full recovery. Should I conclude that the Lifesavers are a cure for Covid?
I'm not certain why you're convinced that this isn't a real problem that can be induced by PWM. There are loads of studies in healthcare about it, and how it works -- which we've summarized accurately in this piece in conjunction with physicists, and neurologists. We've also discussed that it's rare, and who it's most impactful for.
I'm not sure what your agenda is, and you need to stop.
I don’t doubt that it’s real. I am genuinely curious as to how they differentiate a case caused by flicker vs a case caused by a virus. I would imagine that accurately diagnosing the cause is helpful in determining the best treatment.
As I mentioned in my last reply.
I started on my new phone around lunchtime. I went to bed early that night with a shocking headache. Looking back I’m just gutted I didn’t make the connection and kept using the device.
With the later, such as with PWM dimming, the light source itself is turning on and off and your brain is supposed to interpret that as either a dimmer or brighter screen. In the case of an OLED screen, the pixels are both the light source and the image source so the image itself is essential turning on and off repeatedly depending on the desired brightness. This seems to cause more eye strain for some people than how it was traditionally done with LCDs as described above.
But, as I wrote, the frequency matters. A 50% duty cycle at 30 Hz is not going to be the same as 120 Hz or 1 kHz. And human eyes don't have infinite temporal resolution.
Just like pixels smaller than a certain size are no longer distinguishable, flickering faster than a certain frequency should also no longer be distinguishable. I don't know what the threshold may be (and it probably varies from person to person), but my gut tells me that there should be a frequency above which should be indistinguishable from actually-dimmed pixels.
Comments
In terms of weight, the iPad is about as heavy as a typical hardback book.
For all those stating you feel some pain or strain with the OLED screens etc but you're gonna give it a few weeks to see how it goes, please reconsider this.
I am almost three years with pain after an iphone 12pro gave me a headache, two weeks later I went back to my 11 and the pain started to subside, but the damage was done.
I have paid hundreds with a private neurologist who has diagnosed me with New Peristent Daily Headache(NPDH). The pain never goes, and never will. Usually brought on by viral infection but can be triggered but other means, repetitive eye strain being one. It triggers pain within glands in the brain.
I have tried lost of drugs, some which have been effective but the pain breaks through them after time. Next treatment once my current one fails is botox therapy, 37 injections in my scalp every 10 weeks.
Appreciate this PWM issue is only a very small percentage of users, and the chance of someone also getting my condition is even lower but if there is pain, please stop.
I would gladly use a Nokia 3310 for the rest of my life if it meant my condition went away.
Human beings are biologically trained to assume cause and effect when two things happen at the same time. Often, there really is cause and effect, but sometimes it is just coincidence. Eat at a new restaurant and get sick the next day, and most people would conclude that the restaurant was the cause of the sickness, but it is also possible that the sickness was from some other cause, and it was just coincidental that you ate at a new restaurant.
When I was sick in bed with Covid, I ate a lot of cherry Lifesavers®. I ended up with a mild case and a full recovery. Should I conclude that the Lifesavers are a cure for Covid?
I am currently under the care of one of the best headache neurologists in UK, possibly the world. It’s seems you’ve googled my condition and diagnosed me.
My condition, as you say, can be brought on by a viral infection. However head traumas, surgery, exposure to certain elements such as strong fumes or bright flashes of light can also cause this. One of its characteristics is that you can pinpoint the exact time when it started, which for me, was the day I used my new phone.
It’s a fairly new condition but my neurologist and his team have noted an increase in recent years and the amount of screen time people have these days is probably not a coincidence.
My optician has so many more children wanting glasses from a younger age.
Theres a lot of folk who struggle with OLED but that number is about to shoot up once more and more use VR headsets with a screen so close to their eyes.
I just wish I had stopped with the phone and it not taken 2/3 weeks for my to realise that was the cause of my eye fatigue and headache.
I’m not some flat earther with uneducated beliefs. It’s science, and I’m happy that big hitters in the media world such as Apple Insider are starting to highlight the issues, hopefully more do the same which eventually forces Apple, Samsung etc to add options where PWM and OLED become safer.
I started on my new phone around lunchtime. I went to bed early that night with a shocking headache. Looking back I’m just gutted I didn’t make the connection and kept using the device.