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ono · 01-31-2019, 07:50 AM

Hello everyone,

This is my first post here. So far I was satisfied user of Inkpad 1. This device works as expected, the only reason I was looking for alternative was blue (non-natural) back-light - especially for late reading and rather high weight of 350g.

Kobo Forma looked like a great replacement, both in terms of the weight & design and natural (yellowish) light. So this Monday I have ordered one. Later that day I came across PWM back-light flickering issues (reading this forum) - I was a bit disappointed, as I am in principle against PWM (my reasoning below) and I am carefully checking all devices and LED light bulbs against PWM in my home. This time I was ordering online and it hasn't occurred to me that eReader can have PWM.

So I took the PWM claims with a grain of salt, and decided to give it a try and test it myself. The device arrived to me Tuesday. I opened the box and took my iPhone XR and I was (unfortunately) able to reproduce flickering in slo-mo. Like some of you have noticed, newer iPhones have some sort of PWM adaptation so flickering was visible just for a short while when I move my camera towards Kobo Forma. I took my wife's iPhone SE and there it seems there is no PWM adaptation in slo-mo at all, so the flickering was more obvious and visible all the time - you can find my footage there: https://www.youtube.com/watch?v=o4U-TZt-W8U

The device has been updated to the latest firmware before making the video. Finally, I have decided to return it.

Now I little bit info why I am generally against PWM. While like most of us know, with high enough frequency the brain no longer recognizes screen flickering. As far to what I have read, depending on the viewing angle, individual sensitivity etc. this may be lie somewhere in between 100-200 Hz. So it is very individual. Despite there are no hard proves that PWM has or has no negative (even irreversible) effects on your retina, I believe the peak energies of PWM still reach the retina and depose certain energy.

You may imagine that with some extreme PW modulation scheme that has really long blanks (pauses) and really short pulses of high intensity light, in overall your brain will average it out and perceive it as dim screen. However, the high intensity pulses will still reach and depose the rather high energy on the optic nerve and I can imagine this may cause higher strain of the nerve than continuous low intensity signal energy deposition. In super extreme case you may even "burn" your retina - e.g. with a short laser pulse.

This is nowhere any kind of proof, but simple reasoning. Too bad that Kobo remains silent to PWM allegations or simply denies them - I have seen someone that reported PWM issue to them, but they replied they cannot reproduce it. Well, I could.

To bad also they set the new "standard" where you can really see the PWM, while the others either don't do PWM at all, but rather control the light with voltage (I know it may be less energy efficient), or simply they use super high PWM frequencies (so cannot be seen with 240fps slo-mo).

Finally, I am happy that there are still some flicker (PWM free) devices released, e.g. iPhone XR (while more expensive iPhone X/XS is not) also new iPad. Time will tell what impact all this new "superior" OLED & PWM tech will have on our health, anyways I don't want to test that on myself or my relatives

Cheers,
-- Adam

01-31-2019, 07:50 AM	#35
ono Junior Member Posts: 1 Karma: 10 Join Date: Jan 2019 Location: Switzerland Device: PocketBook Inkpad 1	Hello everyone, This is my first post here. So far I was satisfied user of Inkpad 1. This device works as expected, the only reason I was looking for alternative was blue (non-natural) back-light - especially for late reading and rather high weight of 350g. Kobo Forma looked like a great replacement, both in terms of the weight & design and natural (yellowish) light. So this Monday I have ordered one. Later that day I came across PWM back-light flickering issues (reading this forum) - I was a bit disappointed, as I am in principle against PWM (my reasoning below) and I am carefully checking all devices and LED light bulbs against PWM in my home. This time I was ordering online and it hasn't occurred to me that eReader can have PWM. So I took the PWM claims with a grain of salt, and decided to give it a try and test it myself. The device arrived to me Tuesday. I opened the box and took my iPhone XR and I was (unfortunately) able to reproduce flickering in slo-mo. Like some of you have noticed, newer iPhones have some sort of PWM adaptation so flickering was visible just for a short while when I move my camera towards Kobo Forma. I took my wife's iPhone SE and there it seems there is no PWM adaptation in slo-mo at all, so the flickering was more obvious and visible all the time - you can find my footage there: https://www.youtube.com/watch?v=o4U-TZt-W8U The device has been updated to the latest firmware before making the video. Finally, I have decided to return it. Now I little bit info why I am generally against PWM. While like most of us know, with high enough frequency the brain no longer recognizes screen flickering. As far to what I have read, depending on the viewing angle, individual sensitivity etc. this may be lie somewhere in between 100-200 Hz. So it is very individual. Despite there are no hard proves that PWM has or has no negative (even irreversible) effects on your retina, I believe the peak energies of PWM still reach the retina and depose certain energy. You may imagine that with some extreme PW modulation scheme that has really long blanks (pauses) and really short pulses of high intensity light, in overall your brain will average it out and perceive it as dim screen. However, the high intensity pulses will still reach and depose the rather high energy on the optic nerve and I can imagine this may cause higher strain of the nerve than continuous low intensity signal energy deposition. In super extreme case you may even "burn" your retina - e.g. with a short laser pulse. This is nowhere any kind of proof, but simple reasoning. Too bad that Kobo remains silent to PWM allegations or simply denies them - I have seen someone that reported PWM issue to them, but they replied they cannot reproduce it. Well, I could. To bad also they set the new "standard" where you can really see the PWM, while the others either don't do PWM at all, but rather control the light with voltage (I know it may be less energy efficient), or simply they use super high PWM frequencies (so cannot be seen with 240fps slo-mo). Finally, I am happy that there are still some flicker (PWM free) devices released, e.g. iPhone XR (while more expensive iPhone X/XS is not) also new iPad. Time will tell what impact all this new "superior" OLED & PWM tech will have on our health, anyways I don't want to test that on myself or my relatives Cheers, -- Adam Last edited by ono; 01-31-2019 at 07:56 AM.