And “Pulse Width Modification” just describes a particular dimming mechanism - lengthening the dark period of the flicker to reduce the average amount of light. As we know, devices and lights can definitely flicker even if they haven’t been engineered to use PWM as the dimming mechanism.
Many of the LED lights that trigger my concussion-like symptoms don’t use PWM dimming, but do have “invisible” flicker. Really bad ones have 100% flicker at full brightness - without any PWM. (And some of these flickering LEDs are erroneously marketed as “flicker-free.”) For me, if there’s also PWM being implemented to dim the lights, my symptoms tend to become more intense faster than if the same lights are at full brightness (and all that I’ve tried so far in this category also flicker at full brightness). Even without PWM being used, fairly subtle LED flicker (some measured at as low as 0.7% flicker) can trigger my symptoms in less than 20 minutes.
Another issue with lights, which might also happen with screens, is that the max brightness that the user can get may not actually be 100%. In a building where I used to work, they said after an LED remodel that they “trimmed” the lights (strip lights controlled by a power supply) to reduce the brightness to a tolerable level - meaning that the max brightness we could get from the dimmer switch ourselves was about 95% and had a little more flicker than it would have had at 100% brightness. These lights flickered and triggered my symptoms even though PWM wasn’t added as a dimming mechanism until a much lower setting - and if I dimmed them as low as possible into the PWM range my symptoms were worse.
I own 2 brands of completely flicker-free LED bulbs that never trigger my symptoms. One of these kinds can be dimmed and doesn’t use PWM for dimming.
I know that some of my issues with screens triggering my symptoms can be due to backlight flicker - on screens where there’s obvious PWM dimming, maxing out the backlight brightness helps me. However, that’s definitely not sufficient to prevent my symptoms from starting fairly quickly from screens - dithering flicker is definitely triggering for me, but I’d guess that subtle backlight flicker and flicker from pixel inversion are probably also triggering for me. I also suspect, but don’t have a way to measure, that Apple may increase the dithering flicker as the backlight dims on my iPhone SE 2022. It isn’t supposed to have PWM dimming and isn’t supposed to have a flickering backlight, but dimming the screen makes my symptoms start faster, similarly to how my symptoms start faster if I try altering the color palette, which I suspect may be done through extra dithering. Currently I keep the screen at full brightness, but put Dim-It sheets over it - still not enough, but it helps.