Why Apple Vision Pro's constant strobing matters to your health

Posted:
in Apple Vision Pro edited February 7

The Apple Vision Pro uses a common technology that is at the core of some of the health warnings about the device. Here's what that technology is, why it's crucial to the headset, and why it may cause problems for some users.

Close-up of the inside of Apple Vision Pro resting on a white surface, lenses reflecting a room
Inside of Apple Vision Pro



An obvious potential health issue with Apple Vision Pro is motion sickness. Apple has paired a lot of technology together to help minimize that. There is a rarer and more severe potential health issue associated with the headset, though.

In short, the Apple Vision Pro is constantly flashing the user. It's not as obvious as a strobe light at a rave or party, but it is happening constantly.

And, some people are susceptible to potentially serious health issues from those strobing lights.

Video game publishers have warned about this kind of thing for some time, and the concept has been used by trolls to attack people with epilepsy. But, the Apple Vision Pro isn't a screen at a distance, and it is literally strapped to a user's face with little or no outside light getting in to help blunt the impact of that strobing.

Here's why that all matters, and who it matters to.

Health issues from strobing lights, and who is affected



We are not medical doctors here at AppleInsider, but this author had a child that was profoundly epileptic, and we did talk to neurologists before writing this article. We're comfortable writing this article given this mix of practical experience and professional consultation.

There are three main types of health impacts from strobing lights -- flicker vertigo, photosensitive epilepsy, and general photosensitivity.

Flicker Vertigo happens at refresh rates between 1Hz and 20Hz, and can cause disorientation, nausea, and rapid eye movement.

It was first spotted in early helicopters, watching the sun strobe through a rotating helicopter blade. It is less common on the road, but still can be seen by the driver and passengers as the sun filters through trees as a car drives through a lightly wooded area.

Flicker Vertigo is common, but fortunately the symptoms vanish when the strobing stops. It is not incredibly relevant to Apple Vision Pro owners, unless they are hit with maliciously crafted content -- which as we've mentioned happens from time to time.

Photosensitive epilepsy is far less common, but far more dangerous. While sensitivities vary, any strobing can induce a seizure in folks with photosensitive epilepsy, and the individual circumstances and severity of the seizure can vary, person to person.

And, it is possible for somebody to not have any other outward signs of epilepsy, and still be susceptible to specific photosensitive triggers that they previously weren't aware of.

Other health conditions can be aggravated by strobing light. A very high percentage of traumatic brain injury sufferers report photosensitivity, as do people with migraines, frequent tension headaches, or cluster headaches. If you've ever been told you have photophobia, the Apple Vision Pro also is probably not for you.

Sensitivity to strobing lights is also aggravated by fatigue of any sort, diet, time of exposure to the strobing and a host of other situations. If you're well-rested, you may not be sensitive to strobing lights.

If you've skipped a meal, had the headset on watching all of the Marvel movies on Disney+, and didn't get any sleep the previous night, that's about the worst-case scenario.

In all of these cases, the situation is aggravated as more of the user's field of vision is impacted by the strobing. In the case of the Apple Vision Pro, the user's entire field of vision is covered by the strobing from the Pulse Width Modulation used to control the screens' brightness and color mix. More on what that is in a bit.

Clearly, not everybody is impacted by strobing lights. This is good, considering the LED light bulbs that have replaced incandescent lights flicker, although less than the fluorescent bulbs that were a stop-gap between the Edison incandescent bulb and the newer LED. That's cold comfort to the people who are hit, though.

What is Pulse Width Modulation?



There is a lot to Pulse Width Modulation in electronics as a whole, but as it pertains to Apple Vision Pro, Pulse Width Modulation is what Apple uses to regulate the brightness of individual color cells in the eye displays.

An incandescent bulb that can dim throws off fewer photons when at a lower wattage, roughly proportional to the magnitude of the cut in power. Provide half the power to an incandescent bulb, and it will be about half as bright. It does not turn off quickly and strobe -- it just emits fewer photons because of the lower power.

In an OLED display such as that used in the Apple Vision Pro eye screens, brightness control and color mixing is accomplished by turning individual color cells on and off very quickly. If full power, constantly, is being applied to a color cell, then that cell is "on time" or at a 100% duty cycle, and is fully bright.

Pulse width modulation and duty cycle example - credit circuitdigest.com
Pulse width modulation and duty cycle example - credit circuitdigest.com



While there is an overall screen refresh frequency factor to consider as it pertains to health, in short, given a fixed frequency, to reduce the brightness, the color cell is extremely rapidly turned on and off. A 50% duty cycle has the cell on or off half of the time, and is about half the brightness. It also effectively strobes the user at a different frequency than the display as a whole is doing.

Pulse Width Modulation has been used in OLED iPhones since the iPhone X, and it is vital to the operation of the screen. It has always been a concern at some level, to some people. However, the iPhone is a hand-held device, not occupying the about-105 degree field of vision that the Apple Vision Pro maintains, with the rest of the field of vision in darkness.

How bad is this?



We've been watching for reports of photosensitivity as it pertains to the Apple Vision Pro since launch. There are periodic social media reports of headaches and fatigue, as there are with any virtual reality headset.

After all, in the case of the Apple Vision Pro, you're strapping about a pound and a half to your face. There will be fatigue.

Apple Vision Pro doesn't seem any more or any less susceptible to photosensitivity of any sort than any other headset. Apple doesn't trumpet special features to limit that kind of thing, and we assume that there's no real way to engineer around it.

That doesn't make it any more dangerous in Apple Vision Pro versus any other headset, or less worthy of mention, though.

The advice is clear from the doctors we've spoken to, and from Apple itself. If you start feeling strange in any way while using Apple Vision Pro, take it off right away, and talk to your doctor about it.

And, watch for symptoms in folks that you care about that are new owners. It's easy to get over-excited about new technology, and use it for far more than you should in the early days.



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Comments

  • Reply 1 of 32
    Very interesting information. I am enjoying all of your articles regarding Vision Pro and looking forward to future reads. AppleInsider is becoming a valuable Vision Pro resource.
    OferjSnivelylolliverAnilu_777chasmbyronl
  • Reply 2 of 32
    That is interesting.  Many of us can get Migraine Auras from too many sparkly lights or too much blue light.  I think of these Auras as an epilepsy like cascade failure that’s confined to the visual cortex.  You just have to get yourself to a dark quiet place and chill and it resolves.  No headache and on a good day just 20-30minutes.  You do loose partial vision and if you ignore it bad things start to happen. Hopefully someone is thinking about that too.
    OferjSnivelyAnilu_777
  • Reply 3 of 32
    Mike WuertheleMike Wuerthele Posts: 6,827administrator
    JB1567 said:
    That is interesting.  Many of us can get Migraine Auras from too many sparkly lights or too much blue light.  I think of these Auras as an epilepsy like cascade failure that’s confined to the visual cortex.  You just have to get yourself to a dark quiet place and chill and it resolves.  No headache and on a good day just 20-30minutes.  You do loose partial vision and if you ignore it bad things start to happen. Hopefully someone is thinking about that too.
    Sounds like a visual migraine. I've had two or three in my life.

    There's a lot of research going on right now that associates migraine activity with epilepsy centers and neuronal electrical reaction cascades. It's pretty fascinating, but it's also very early.
    edited February 7 OfertenthousandthingsjSnivelyAnilu_777chasmbyronl
  • Reply 4 of 32
    Thank you very much for writing this article.  I am very sensitive to display flickering, and find that OLED displays in general are very problematic for me due to the induced headaches and eye fatigue.  I think it is possible that at some point in the future, it may be seen as a huge mistake to use OLED and similar display technologies that use PWM due to the health impacts that are largely being ignored.  
    edited February 7 OfertenthousandthingsjSnivelyAnilu_777grandact73byronl
  • Reply 5 of 32
    Mike WuertheleMike Wuerthele Posts: 6,827administrator
    mathpunk said:
    Thank you very much for writing this article.  I am very sensitive to display flickering, and find that OLED displays in general are very problematic for me due to the induced headaches and eye fatigue.  I think it is possible that at some point in the future, it may be seen as a huge mistake to use OLED and similar display technologies that use PWM due to the health impacts that are largely being ignored.  
    You're very welcome.
    OfertenthousandthingsjSnivelychasmbyronl
  • Reply 6 of 32
    This is all very useful, thank you. I’m also in the children-with-intractable-epilepsy club (no longer a child, though, late twenties), so clear, aware information like this from someone who understands the stakes is helpful for asking questions of doctors and the like.
    jSnivelyAnilu_777chasmbyronl
  • Reply 7 of 32
    jimh2jimh2 Posts: 588member
    Probably the best written in most informative post I’ve read on Apple Insider. It’s a topic that most would never consider. 
    tenthousandthingsjSnivelyfred1chasm
  • Reply 8 of 32
    Interesting.

    I have a Meta Quest 3 and I noticed that in Pass-Through mode, some of my lights flicker. It successfully compensates for my Hue lights, but the fancy 1-10volt dimming protocol for the other lights (Modular) flicker like crazy when wearing the headset.
    In order to compensate for the flickering the refresh-rate so to speak needs to align to the frequency of the lights. 

    I have migraines; 5 or 6 every year, which start as a visual spiky star and then slowly blinds me from the center. I have over-the-counter pills with me that successfully counter the blindness but my head remains dull and heavy for days, and when I bend over to grap something off the floor, the feeling of migraine comes back - like a warning shot. During the migraine I want to be in bed and total darkness. My eye laser operation years ago worsened these, because it caused dry eyes.

    Things that contribute to triggering them: 
    - reading from a screen with dry eyes
    - being tired 
    - after I recover from a high intensity workout 
    - overly powerful car lights 

    So far, the Meta Quest did not trigger any form of migraine. But it does help to use eye drops during the day. 
    Anilu_777
  • Reply 9 of 32
    mfrydmfryd Posts: 216member
    It's the frequency, not the duty cycle that's important.  Many Modern LED lights flicker at 100Hz or 120Hz depending on where you are in the world.  TV Screens flicker somewhere between 25Hz and 240Hz, depending on what you are watching and the specific TV.   

    Video games have warnings because they may have content that includes explosions.  These explosions may included flashes of light that are turning on/off 7 to 10 times per second (that's 7Hz to 10Hz).

    My understanding is that the Apple Vision Pro has a refresh (flicker) rate of at least 90Hz.  That's not typically an issue
    Anilu_777
  • Reply 10 of 32
    Mike WuertheleMike Wuerthele Posts: 6,827administrator
    mfryd said:
    It's the frequency, not the duty cycle that's important.  Many Modern LED lights flicker at 100Hz or 120Hz depending on where you are in the world.  TV Screens flicker somewhere between 25Hz and 240Hz, depending on what you are watching and the specific TV.   

    Video games have warnings because they may have content that includes explosions.  These explosions may included flashes of light that are turning on/off 7 to 10 times per second (that's 7Hz to 10Hz).

    My understanding is that the Apple Vision Pro has a refresh (flicker) rate of at least 90Hz.  That's not typically an issue
    It's both, right? As per the neurologists and physicists we spoke to for this piece, If a OLED segment has a variable duty cycle, that alters the neurological impact frequency regardless of persistence of vision's perception of the light too. This is practically demonstrated in your explosions example.
    edited February 7 Anilu_777gatorguy
  • Reply 11 of 32
    Provide half the power to an incandescent bulb, and it will be about half as bright. 
    Not true.  It will be much less than half as bright.  When the power drops, the bulb cools off.  This causes the color spectrum to shift away from visible light into more infrared (even fully powered incandescents produce mostly infrared, that's why they are so inefficient).  This color shift is easily visible, that's why a dimmed incandescent looks so much redder than a bright one, and all the blues disappear.  Dim it enough, and you'll just be producing infrared, but still using power.  Then you've got a space heater.

  • Reply 12 of 32
    mfrydmfryd Posts: 216member
    mfryd said:
    It's the frequency, not the duty cycle that's important.  Many Modern LED lights flicker at 100Hz or 120Hz depending on where you are in the world.  TV Screens flicker somewhere between 25Hz and 240Hz, depending on what you are watching and the specific TV.   

    Video games have warnings because they may have content that includes explosions.  These explosions may included flashes of light that are turning on/off 7 to 10 times per second (that's 7Hz to 10Hz).

    My understanding is that the Apple Vision Pro has a refresh (flicker) rate of at least 90Hz.  That's not typically an issue
    It's both, right? As per the neurologists and physicists we spoke to for this piece, If a OLED segment has a variable duty cycle, that alters the neurological impact frequency regardless of persistence of vision's perception of the light too. This is practically demonstrated in your explosions example.
    High Definition Broadcast TV in the US has about 30 frames per second.  Most HD TVs will display each frame twice for a 60Hz refresh rate.

    On broadcast TV, an explosion with lights flashing six times per second will have the lights flash on and off, with each cycle lasting about 5 frames.   As with video games, it is the flashing of the content that's the issue, not the much higher flashing of the display media.

    In the old day, a movie in the theater had 24 frames per second.  Originally, that was 24 flashes each second.  A typical human can notice this flicker, especially out of the corner of your eye.  The solution was to flash each frame two or three times.  This brought the flashing of the media up to 48 or 72Hz.  High enough not to bother the vast majority of people.

    The Apple Vision Pro has a media frame rate above 90 Hz.  In terms of bothering people, it should have less of an effect that watching a traditional movie in a movie theater.

    As to variable duty cycles, that is how modern light dimmers work.   If you have been in a room, and lights were dimmed below full brightness, you have experienced the effects of a variable duty cycle at 60Hz (or 50Hz in most non-USA countries).   If you had no problem in a room with a high quality dimmer (no noticeable flickering), than you should have no problem with the Apple Vision Pro.

  • Reply 13 of 32
    Mike WuertheleMike Wuerthele Posts: 6,827administrator
    bonobob said:
    Provide half the power to an incandescent bulb, and it will be about half as bright. 
    Not true.  It will be much less than half as bright.  When the power drops, the bulb cools off.  This causes the color spectrum to shift away from visible light into more infrared (even fully powered incandescents produce mostly infrared, that's why they are so inefficient).  This color shift is easily visible, that's why a dimmed incandescent looks so much redder than a bright one, and all the blues disappear.  Dim it enough, and you'll just be producing infrared, but still using power.  Then you've got a space heater.

    I appreciate the extra context, and I'm fully familiar with the shift and I^2R losses, and so forth. This piece is not about the incandescent so much as it is about PWM. Hence, it is close enough to half to say "about" for the purposes of this text. 
    edited February 7 gatorguy
  • Reply 14 of 32
    doggonedoggone Posts: 373member
    If this does become a major issue for a good number of people, the technology will have to adapt.  For example, if you want to dim a certain area say 5 x 5 pixels by fifty percent, don't switch off all at the same time 50% of the time.  Instead interleave the cycling on and off at a greater period of time off so that average intensity for that area is lowered by 50% but the effect is spread out across the time frame.  That way the dimming effect is spread out and flashing effect minimized.  It will be more complex to manage that way but would be easier on the eyes.
    asus389
  • Reply 15 of 32
    I wonder how many of us that are ADHD/autistic/sensory processing issues will run into problems with this?

    I've found a "Galaxy Ball"sold at the Barnes and Noble that when bounced, flashes in a pattern that if I were subjected to it too long, would push me right into sensory overload within minutes. Your mileage may vary. Having something completely control your total vision with such possible scenarios is potentially far more problematic, and oddly enough, the better the technology for how quickly it can turn on and off, the more potential problems exist for a larger percentage of the population, depending on what's being displayed. That's the one thing many people talking about movie theater screens or TV screens are perhaps forgetting: you have other things to look at in your field of vision to balance against it as well.

  • Reply 16 of 32
    FINALLY an article about pwm on the front page! I’ve had to stick with an old iPhone 11 due to all other iphones being oled with pwm. Same for the new devices with mini led. Though high frequency, they still also flicker and give me issues. It really is a struggle to get new devices in this pwm and colour dithering era. 

    Pwm is one thing, but there is the dithering aspect too. That is when Apple tries to get an 8bit panel to show 10bit colours, by flickering individual pixels through certain colours to create new ones that that panel shouldn’t be able to support. Hence being able to offer the p3 colour gamut on other devices than their hdr expensive screen. 

    I miss the days of DC dimming, before the cheaper pwm dimming took over to save a buck (and energy probably). 

    Thank you thank you thank you. More of this please. 
    mathpunk
  • Reply 17 of 32
    ruoma said:
    FINALLY an article about pwm on the front page! I’ve had to stick with an old iPhone 11 due to all other iphones being oled with pwm. Same for the new devices with mini led. Though high frequency, they still also flicker and give me issues. It really is a struggle to get new devices in this pwm and colour dithering era. 

    Agreed.  I also am staying with the iPhone 11 until it breaks, then I am not sure what I will do.  Hopefully articles such as this one will draw more attention to the issue and motivate Apple to continue offering an LCD model or something else comparable.
    edited February 8
  • Reply 18 of 32
    Thanks for writing this. I able to tolerate most screens but I have struggled to make the transition to OLED screens, presumably for the reasons you mention in this article. OLED phones give me headaches, eye strain, and generally make me more tired than the older LCD screens. 

    I've held on to my older LCD iPhone as a result but as time has passed its been harder and harder to continue using it as newer apps assume larger screens, faster processors, and improved capabilities of the newer iPhones that all have OLED screens.

    I really wish Apple would offer some accessibility settings to help mitigate the increase in flicker that comes with these displays. They do a very good job with accessibility in other areas.
  • Reply 19 of 32
    I agree with you dear Author, I am using Vision Pro and noticed, after I take out my Vision Pro after 1-2 hours use, I feel little bit discomfort, fatigue, red eye, itching etc. I am leaning towards returning. 
  • Reply 20 of 32
    zakool21 said:
    Interesting, my prior comment was deleted somehow. 

    I'm curious why this is now becoming a topic of interest. Let's say 5% of people can afford the Vision pro. About 1% of the population has epilepsy, and less than 5% of that population has photo-sensitive manifestations. 

    Standalone HMDs have been a thing since 2009 when the Oculus Quest came out, and for years before that with tethered headsets. Why is this now a topic of discussion? 
    It's a topic of interest here and now because this is an Apple-oriented website and Apple released the Vision Pro last week.

    Congratulations on possessing the ability to Google information about epilepsy populations. It doesn't sound like you have any experience with those populations. Epilepsy is often accompanied by comorbidities like the autism spectrum, learning disabilities, and visual differences/impairments. Regardless, technology is worth talking about from a health standpoint, and for Apple customers, this is new technology. 
    edited February 8
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