“Flicker Free certification” is a bit of an oxymoron.Forgive me for not having citations handy (might be able to find some later), but there's been some discontent about what these certifications actually mean in practice. TUV Rheinland with their "Eye Comfort" certification seems to be the most popular, but the flaw is outside of a strict outline of requirements the actual testing methodology seems to be unavailable for public scrutiny. Some people in other communities have claimed that with some devices that are certified they don't use explicit PWM, but they still potentially suffer from ripple of the backlight, leading to still being an issue. And even if the certification was entirely honest it could still lead to a false sense of security due to per unit variance or the manufacture switching components without changing the model number (there is prior precedent for this, see "panel lottery").
All of the smartphones I’ve seen with the certification still flicker, they just do it at a higher frequency and assumedly lower modulations. Hence PWM-sensitive users can still find these displays to be headache-inducing and potentially unusable.
Apple would probably meet all of TUV Rheinland’s Eye Comfort criteria besides the Flicker Free certification, which indicates they have a lot more work to do with the flickering of these displays.
I’ve tried looking up the exact guidelines and requirements for these certifications, including “eye-friendly,” etc. This is for the most part what I could find beyond the description of why it matters, including increased readability and reduced headaches/migraines:
“TÜV Rheinland has tested this product to ascertain whether the display produces visible and invisible flicker for the human eye and therefore strains the eye of the user.
TÜV Rheinland has defined a catalogue of tests, which sets out minimum standards at various frequency ranges. The test catalogue is based on internationally applicable standards or standards common within the industry and exceeds these requirements.
The product has been tested in the laboratory according to these criteria.
The keyword "Flicker Free" confirms that the device has no visible and invisible flicker defined in this standard within the range of 0 - 3000 Hz under various brightness settings.”
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