It's not about whether you can "see 240Hz". CRT phosphors have sustain, while OLED does not. The fully-on, fully-off cycle, if infrequent enough, causes some sort of visual stimulation that some brains absolutely do not like. You don't have to see it to feel it.
Sometimes I can tell flickery fixtures because they just "feel more staticky". I don't get visual eyestrain or nausea though.
What exactly do you mean by "not the same thing"? Using a device means moving your eyes, among other things. I don't exactly stare at a specific point on the screen for the 63 Hz visual persistence to take effect and I'm pretty sure 95% of the other individuals of this world don't do that either
Other than some old monochrome CRTs, all CRT phosphors decay too fast to prevent flicker. You get some softening of the trailing edges of the phantom array images, but they're not actually blurred together like on a sample-and-hold display. And even the fastest CRTs have fairly low refresh rates, making it more obvious.
The problem isn't the flicker directly (240Hz is above the flicker fusion threshold), it's the phantom array effect when you move your eyes. Static images transform into a series of overlapping images, and this can be annoying and distracting. It's visible well into the kilohertz depending on how strong your saccadic masking is. I can personally see PWM up to about 10kHz (tested using a strobing LED).
AFAIK, all OLED displays have PWM flicker, and for this reason I stick with LCD, where flicker-free displays are available (although PWM flicker is present in some LCD displays too).
Like CRTs scan slower than that, and almost no-one could say they could see the pixels being drawn.
Sure you could hear those fuckers, but not see them, unless you had a source of vibration nearby.
Howe much of this is measurable, and how much of it is similar to the Himalayan salt lamp stuff?
Sometimes I can tell flickery fixtures because they just "feel more staticky". I don't get visual eyestrain or nausea though.
It's not magic. :) You DO see it. 500 Hz for the median observer; above 800 Hz for some individuals. https://doi.org/10.1038/srep07861
There is still some ability to percieve strobing at a steady state though, even if the amplitude is reduced by visual persistence.
Other than some old monochrome CRTs, all CRT phosphors decay too fast to prevent flicker. You get some softening of the trailing edges of the phantom array images, but they're not actually blurred together like on a sample-and-hold display. And even the fastest CRTs have fairly low refresh rates, making it more obvious.
what about old-timey film projection? thats ten times slower and fully on/off?
AFAIK, all OLED displays have PWM flicker, and for this reason I stick with LCD, where flicker-free displays are available (although PWM flicker is present in some LCD displays too).