[HN Gopher] PWM flicker: Invisible light that's harming our health?
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PWM flicker: Invisible light that's harming our health?
Author : SLHamlet
Score : 53 points
Date : 2025-06-18 17:32 UTC (5 hours ago)
(HTM) web link (caseorganic.medium.com)
(TXT) w3m dump (caseorganic.medium.com)
| mtalantikite wrote:
| These LED light flickers actually trigger ocular migraines for
| me. I had tried to put in LEDs when the incandescent ban hit the
| US, and ended up with a Philips Hue system. I had 4 migraines in
| 3 days and had to send them back. I purchased as many
| incandescent bulbs as I could find, but they were somewhat
| impossible to find at that point.
|
| I've got a couple bulbs from Waveform Lighting and they don't
| flicker, but I totally can tell the reds are off.
|
| I really hate the LED transition. My building replaced all the
| outdoor lights with them, and now it's just too bright to sit on
| my stoop at night like used to be so common here in Brooklyn. My
| backyard neighbor put in an LED floodlight and now I have to buy
| blackout curtains. I drive rarely, but the oncoming headlights
| are blinding when I do. It's pretty depressing if I think about
| it too much.
| igor47 wrote:
| That sucks; I feel your pain. I, too, strongly dislike overly
| bright lighting.
|
| I wonder if there's room to at least engage with the neighbor
| to talk about friendlier light options? You might also be able
| engage with these folks to see if there are efforts to improve
| the lighting in new York: https://darksky.org/
| PaulHoule wrote:
| My take is that PWM dimmers are dramatically more energy
| efficient than the old rheostat dimmers people used to use. If
| you operate a transistor in a digital mode where it is either
| on or off it is close to 100% efficient, but if you operate it
| in a 50% power mode you have to send 50% of the power to a load
| and the other 50% to a resistor. Thus CMOS logic eradicated
| bipolar, switching power supplies replaced linear power
| supplies, a Class D amplifier can be a fraction the size of a
| Class A amplifier, etc.
|
| You could probably still reduce the flicker by either
| increasing the switching frequency or putting some kind of
| filter network between the switch and the load.
| mtalantikite wrote:
| For sure, they're definitely way more efficient. They just
| unfortunately give me migraines. I'd be open to trying some
| that have a filter network or some other smoothing on the
| flicker.
|
| But I've also never lived in a house that has dimmers
| (they've all been old homes in the north eastern US) and I
| never use overhead lighting, so it's not something I need or
| would miss.
| card_zero wrote:
| Apparently fourth-generation LED tube lights are designed
| not to flicker.
|
| https://en.wikipedia.org/wiki/LED_tube#History
| JKCalhoun wrote:
| I wonder to the degree their effects are much worse than
| migraines. Perhaps irritability? Mental confusion? Anxiety? I'm
| spitballing here, but to be sure it seems like our world is
| somehow a place of more anxiety, irritation .... I would love
| for it to be something we could take control of.
| genewitch wrote:
| i doubt it's the light bulbs. I posited the other day, by
| assembling a few different ideas, that Trauma Based
| Entertainment is to blame for this. something like 2/3rds of
| all Television programing is law-enforcement adjacent. True
| Crime is super popular on TV, law and order, NCIS, FBI this-
| and-that. And what's one of the largest advertising cohorts?
|
| Medicine for depression, anxiety, insomnia...
|
| it's nearly a closed loop; something i intuitively realized
| shortly after 2001/09/11 - by the end of that year i decided
| i would no longer have a "Television" attached to
| CATV/SAT/ANT service.
|
| I'm not sure if i am correct, i haven't really dedicated a
| lot of time to getting the exact numbers, talking to
| psychologists and sociologists and the like. But two people i
| know had "breakdowns" (grippy sock) in the last month and
| both of them always have true crime on TV in the background
| or listen to true crime podcasts. Shortly after that happened
| i was listening to the moe facts podcast where Moe used the
| term "trauma based entertainment" and something clicked - Moe
| didn't mention "it's because of pharma ads" - that's my own
| input after having worked for the largest television
| "broadcast" company in the world, just long enough to see the
| advertiser "dinner".
| RiverCrochet wrote:
| The only ones watching traditional OTA TV anymore are
| elders. That advertising cohort is why OTA TV ads are
| filled with pharmaceuticals and "you may be entitled to
| financial compensation" type ads, at least where I'm at.
| Traditional TV has been dying since Youtube and broadband.
| MTV plays Ridiculousness constantly because no one is
| actually watching it.
|
| > it's nearly a closed loop; something i intuitively
| realized shortly after 2001/09/11 - by the end of that year
| i decided i would no longer have a "Television" attached to
| CATV/SAT/ANT service.
|
| Curiously this is about the same time I decided to give up
| on TV and radio as well.
| ToDougie wrote:
| Utter nonsense.
| oakwhiz wrote:
| Lights for high speed cameras use really good filtering on
| their PWM switching, or just linear power supplies. It would be
| nice to have a premium bulb that has longer life and much less
| flickering.
| mousethatroared wrote:
| If you're savvy with manufacturing, make yourself a left handed
| edison thread (I can't find them anywhere). Left handed
| incandecent lightbulbs are still legal
|
| Also, you can buy high wattage lights, and the three ways have
| lower wattage settings.
|
| Finally, outdoor and appliance incandescents lamps are very
| inefficient, but last forever.
| JKCalhoun wrote:
| Suspicious of "DC dimming". If you can just lower the current to
| an LED to dim it, everyone would. Someone will know better than
| me, but I believe there is a kind of threshold voltage for the
| (solid-state) LED.
|
| I am not aware of LED bulbs (and here I am talking about home
| lighting, not phones or laptops) that dim by shutting down some
| of the (multiple) LEDs.
|
| Most home lighting bulbs appear to have several LED elements. A
| circuit could enable dimming by simply shutting some of them off
| -- running the rest full-on. 50% dim would of course shut half
| the LEDs off. No PWM required.
| kjkjadksj wrote:
| You can in fact dim leds. You can see a lot of controllers that
| are just that at various parts suppliers.
| genewitch wrote:
| you can dim LED that are running on DC (it requires more than
| a potentiometer i guess - probably a buck circuit controlled
| by a pot, though) or AC; i have scant idea how the AC ones
| work, although variacs have existed for a real long time; but
| you have to buy special LED bulbs that can handle being on a
| dimming circuit.
|
| this is different than a bulb like hue etc that have the
| ability to dim themselves through whatever mechanism.
| SAI_Peregrinus wrote:
| Traditional dimmers used TRIACs. Those don't dim LEDs well,
| they make _very_ visible flicker. TRIACs turn the AC off
| for part of the waveform, essentially a very slow version
| of PWM. With an incandescent filament that flicker isn 't
| as noticeable since it takes some time to cool down & stop
| glowing, which visibly smooths the flicker. It just
| stabilizies around a lower temperature. With LEDs, the
| turn-off is nearly instant. You visibly see the flicker at
| the AC mains frequency.
|
| There are two ways to dim an LED: supply less current at
| the same voltage, or PWM dim it with a fast enough
| switching speed that you don't notice the flicker (this
| being slower than it needs to be is what the article is
| about). A current source is pretty easy to build, and
| doesn't flicker, but it _does_ dissipate all the excess
| energy as heat. That 's not what you want inside the dimmer
| switch in your wall, it can be quite a lot of heat and
| would be a fire hazard in such a confined area. It does
| work for things like photography lamps which can have
| exterior heat sinking.
| nomel wrote:
| > but it does dissipate all the excess energy as heat.
|
| No. That's only true for a _linear regulator_ , which is
| just one, very terrible, implementation of a current
| source that's only used for very low power applications.
| Linear regulators are never used for things like room
| illumination.
|
| The alternative, and what's used for _all commercially
| available DC LED drivers_ (plentiful and cheap), is to
| just use a regular AC- >DC switching supply in current
| mode (current for feedback rather than voltage feedback).
| The only flicker is the ripple left in the filtered
| output.
|
| Why aren't these used? Because most _dimmer switches_ use
| tech from incandescent age, and just chop off parts of
| the AC sine wave, so the bulbs are designed around the
| switches you can buy in the store. Why do dimmer switches
| chop? Because that 's what the bulbs you can buy at the
| store expect, sometimes damaging them if not dimmed as
| they expect.
|
| You can buy in wall DC dimmer switches from any LED
| supply store, but they require DC lighting, also only
| found at LED supply stores. It's entirely a _very recent_
| momentum problem, that 's slowly going away.
| mrob wrote:
| You can just lower the current. Not everyone does because it
| generally requires more expensive components, e.g. inductors.
| There is a threshold voltage ("forward voltage") needed for
| LEDs to turn on but there's no threshold for minimum radiant
| flux. LEDs are actually more efficient at low current (although
| this might be counteracted by greater losses in the power
| supply).
| Kirby64 wrote:
| DC dimming LEDs is relatively easy, and somewhat common. The
| problem is that it's expensive compared to PWM dimming. It
| requires more expensive current-adjustable circuitry.
|
| Additionally, for bulbs that are used in regular household
| fixtures, they basically need a way to convert TRIAC chopped
| 50/60Hz AC into constant current... which makes things even
| more expensive. Smart bulbs that are supplied a constant non-
| chopped AC can do it easier, but it's still expensive to do DC
| dimming.
| PaulHoule wrote:
| I guess there is some threshold below which the LED turns off
| so the voltage/current -> light function needs to be set
| accordingly.
|
| When I was in high school we were messing around with liquid
| nitrogen and overvolting LEDs and noticed the odd effect that
| the color of the LED would change if you overvolt it. It was
| years before I found out why
|
| https://www.reddit.com/r/AskElectronics/comments/v28qbh/why_.
| ..
|
| https://spectrum.ieee.org/a-definitive-explanation-for-
| led-d...
| Kirby64 wrote:
| Voltage, yes. Current, no not really. You can drive
| extremely low currents and still get photon emissions from
| LEDs. That said, it's highly non-linear, so you basically
| need to assign set points. Doubling the current won't
| double the lumen output.
| normie3000 wrote:
| Do computer screens flicker and release this bad light?
| igor47 wrote:
| In the article they rank some smartphones by how much they
| flicker for dimming, I assume it's the same when computer
| screens dim?
| codethief wrote:
| Some do, some don't. Sites like notebookcheck.net typically
| mention in their reviews whether a given laptop screen exhibits
| PWM.
| layer8 wrote:
| Yes, Notebookcheck regularly measures PWM in displays:
| https://www.notebookcheck.net/PWM-Ranking-Notebooks-Smartpho...
|
| For OLED I remember reading that PWM dimming is necessary
| because DC dimming causes shifts in color/whitepoint.
| blacksmith_tb wrote:
| I would certainly agree that finding LED bulbs that you like
| and/or don't bother you can take some work (especially if you
| want to put them on a dimmer, in which case you may also need to
| replace your dimmer). However, I am skeptical that subtle PWM
| flickering is unavoidable. For the chateau example, it would be
| better to choose bulbs with fewer lumens and run them at 100%?
| baggachipz wrote:
| I wonder about this too. If I have a dimmer and a LED bulb,
| does putting the dimmer all the way up still use PWM? I have a
| hunch that it still does, but would love to be proven wrong.
| demosthanos wrote:
| I know that people anecdotally report complaints about flicker
| and it's plausible to me that there could be an effect, but the
| way this piece is written reminds me distinctly of similar essays
| about WiFi sickness, MSG, and GMOs.
|
| It identifies a "health risk", describes the mechanism in terms
| that sound very convincing, assigns numbers to its cause and
| effects, provides a table grading health risks of various
| products, all without linking to a single scientific study
| demonstrating that the effect is anything other than nocebo. The
| closest they come is a image of a table that refers to a few
| institutions that apparently did a study related to PWM (leaving
| it an exercise to the reader to find the studies they're
| supposedly referencing) and a link to a Wikipedia page which
| links to a Scientific American article which says:
|
| > In 1989, my colleagues and I compared fluorescent lighting that
| flickered 100 times a second with lights that appeared the same
| but didn't flicker. We found that office workers were half as
| likely on average to experience headaches under the non-
| flickering lights. No similar study has yet been performed for
| LED lights. But because LED flickering is even more pronounced,
| with the light dimming by 100% rather than the roughly 35% of
| fluorescent lamps, there's a chance that LEDs could be even more
| likely to cause headaches.
|
| I'm willing to entertain the idea that LED flicker is actually
| problematic, but I wish essays like this would be honest about
| the degree of confidence we have given the current state of the
| evidence. This piece instead takes it as a given that there's a
| problem, to the point where they confidently label devices on a
| scale of Low to Extremely High health risks.
| NhanH wrote:
| IEEE Recommended Practices for Modulating Current in High-
| Brightness LEDs for Mitigating Health Risks to Viewers :
| https://standards.ieee.org/ieee/1789/4479/
|
| There is nothing anecdote about flickering in LED light causing
| health risks.
| demosthanos wrote:
| I am _not_ questioning that certain types of flickering are
| harmful, so that there 's an IEEE standard for how to safely
| use PWM does not contradict what I said.
|
| What I'm asking for is for articles like this that cite
| numbers and provide tables purporting to quantify the degree
| of harm caused by various devices to point to where they're
| getting their numbers from or, if they can't do that, stop
| making up numbers and assigning things to "harm" scales that
| they invented themselves based on vibes.
|
| Either there's a study showing that 246 Hz flickering poses
| "Extremely High" health risks or there isn't.
| NhanH wrote:
| See my comment on the other reply.
|
| > Either there's a study showing that 246 Hz flickering
| poses "Extremely High" health risks or there isn't.
|
| They calculated it using the definition from the standard.
| demosthanos wrote:
| Can you please cite the page number where this definition
| exists? When I search for "extreme" in the standard that
| the other commenter links to I don't turn anything up, so
| I'm unclear where that classification is defined.
| NhanH wrote:
| 31 and 32 (by the printed page number), in pdf it's 42
| Kirby64 wrote:
| The article contradicts the IEEE paper.
|
| They list the 'Xiaomi 15 Ultra' as having a 'Moderately
| High' health risk, and cite it as having a 2.16 kHz PWM
| frequency at 30-75% modulation depth.
|
| The IEEE article has recommended practices that state:
|
| 8.1.2.3 Example 3: PWM dimming Using Figure 20, the
| recommended practice for PWM dimming at 100% modulation
| depth is that the frequency satisfies f > 1.25 kHz. This
| can also be derived using Recommended Practice 1 and
| solving 100% = 0.08xfFlicker. This level of flicker could
| help minimize the visual distractions such as the phantom
| array effects.
|
| Seems like even at 100% mod depth, >1.25 kHz is just
| fine.
|
| Also, the article does not seem to distinguish between
| modulation at reduced brightness, which the IEEE article
| calls out specifically as something that is unlikely to
| cause issues. E.g., movie theaters using film all flicker
| at 48 Hz and nobody complains about that.
| demosthanos wrote:
| That does not define the scale that they're using. That's
| a typical hazard analysis risk matrix which has two axes
| which can be converted into a 4-point scale (Low, Medium,
| Serious, High). Importantly, to do a risk assessment in
| the style of IEEE 1789's you have to identify the
| specific Hazards that you're analyzing, which TFA does
| _not_ claim to be doing in that table, instead speaking
| vaguely of "health risks". IEEE 1789 does not provide a
| mechanism for evaluating "health risks" without
| specifying _exactly_ which risks are being evaluated.
|
| You can see on page 27 how this is meant to be used: it
| should produce a per-hazard matrix.
|
| You might be thinking of Figure 18 on page 29, which does
| identify Low-risk and No-effect regions by Modulation %
| and Frequency, but that also does _not_ claim to identify
| high-risk regions, it just identifies the regions we can
| be highly confident are safe. And importantly, as a
| sibling comment notes, TFA 's table actually contradicts
| the line on Figure 18, labeling several devices as higher
| than Low even when they're squarely within the Low-Risk
| and No-Effect zones.
| PaulHoule wrote:
| Was it an astronomically high health risk to watch a TV set
| that flickers at 60 Hz or movies that flicker at 48 or 72
| Hz? (It is 24 frames per second but you'd perceive a lot of
| flicker at that rate so the shutter has 2 or 3 blades)
| wasabi991011 wrote:
| Here is a non-paywalled link: https://www.lisungroup.com/wp-
| content/uploads/2020/02/IEEE-2...
|
| Sure, PWM light can cause health risks _for some people_ ,
| _in some contexts_. But taking research out of context is bad
| science.
|
| Do you genuinely believe the Pixel 7 and 8 Pro have an
| "extremely high health risk", in the context of what a lay
| person would understand?
|
| Edit: I specify 'lay-person' because clearly this is an
| introductory blog post (or advertisement for Daylight
| Computer). If they want to use a more specific definition of
| health risk, then they better define it.
| NhanH wrote:
| The "very/moderate high" comes from the standard itself,
| which is quantified within the standard. In the context, it
| is about the probability of having issues, while the effect
| (mild to catastrophic) is another axis. Considering that
| they stick to the "official" wording and seeing the
| criticism, I am not even sure if they can change to a more
| "lay-person" friendly and be acceptable to all the critics.
|
| The standard also linked to the researches during their
| discussion.
|
| Please read it, instead of just randomly throw out things
| hoping that they supported your argument.
| demosthanos wrote:
| You can't just point people at a 60-page paywalled
| standard and say "the supporting evidence to my claim is
| somewhere in here, I pinky promise". You are the one
| making assertions, it's on you to prove that the standard
| actually does reflect the text of TFA. I'm not going to
| read the whole standard because I'm not the one making
| the argument and I can't be bothered doing the research
| needed to refute every piece of nonsense science that
| shows up on the internet. What I can do is point out when
| someone is making unsourced claims and insist that they
| provide their sources if they want to be taken seriously.
|
| Cite the exact page number and quote that you claim
| justifies the assertion that 246 Hz PWM carries an
| "extremely high" health risk. Then we can talk.
| NhanH wrote:
| Look, they sourced their claims (quite literally, they
| put how they calculate, from which standard). And linking
| to the correct document is literally how scientific
| citation works -- I replied the page to you above anyway.
|
| If you want to redo the numbers and check if they fit the
| definition, please feel free to do so, but you will need
| to put some works in (since the flicker hz -> risk
| showing in the article is a computed value, you need to
| find the modulation value and plug it in too)
|
| I understand your fight and your idea, I am just saying
| that _in this specific instance_ , this is not a fight to
| be fought. The article is generally correct, and if you
| want to complain about the writing style or it being an
| ads, it's up to you. But this is not the same situation
| with GMO stuffs
| demosthanos wrote:
| > Look, they sourced their claims (quite literally, they
| put how they calculate, from which standard).
|
| No, they said that IEEE 1789 also uses Modulation %
| (which they've renamed Flicker %) to calculate risks.
| That is pointedly _not_ the same thing as claiming that
| they used IEEE 1789 's formulas.
|
| You're reading their copy generously, but that doesn't
| usually pay with marketing copy. Articles like this
| always like to wave in the general direction of official-
| sounding sources while carefully refraining from actually
| claiming that they got their numbers from anywhere in
| particular.
| mrob wrote:
| There doesn't need to be a health risk for it to be annoying. I
| personally dislike PWM and I'll continue to personally dislike
| it even if it's proven safe. Fortunately it's easy to find non-
| flickering LED lights.
| demosthanos wrote:
| If the article said "I find PWM annoying" I wouldn't have
| commented like I did.
| loph wrote:
| I can tell you that lights strobing exacerbate my migraines. Even
| 120 hertz from fluorescent lights will affect me. I have
| mitigated this in the past by adding incandescent lights in my
| office, or demanding to work near a window. LED lamps are no
| good, as another commenter posted, even the simplest ones strobe.
| Incandescent bulbs grow harder to find as time goes on. Progress?
| consp wrote:
| > even the simplest ones strobe
|
| The simplest ones always strobe at line frequency or the double
| of it (due to cheaping out on the power supply). Those have
| visible strobe. Simpel is bad with led light.
|
| Find some not too cheap dimmable warm colored bulbs. They won't
| be cheap but might contain both a high frequency driver and
| fluorescent afterglow and my guess is you will not notice
| anything.
| Jazgot wrote:
| There is a strong and widespread tendency to view anything
| artificial as highly dangerous. I understand this perspective,
| but on the other hand, we have science and reasoned arguments.
| orwin wrote:
| I flagged because this is a submarine ad, but it was still
| interesting tbh.
| satiated_grue wrote:
| "Perceiveved brightness"?
|
| And perceiveved brightness is equal to the peak of the PWM wave?
|
| That image from courtesy Daylight Computer Company is consuming
| too much of my attention.
| SLHamlet wrote:
| I had no idea about this:
|
| "To understand why PWM bulbs have so much flicker, imagine them
| being controlled by a robot arm flicking the on/off switch
| thousands of times per second. When you want bright light, the
| robot varies the time so the switch is in the 'on' mode most of
| the time, and 'off' only briefly. Whereas when you want to dim
| the light, the robot arm puts the switch in 'off' most of the
| time and 'on' only briefly."
| cwillu wrote:
| It's entirely fine if the rate is high enough, but lowering the
| frequency of the PWM and using smaller inductors (or even no
| inductor at all) is a prime way to make the bulbs cheaper.
| bsder wrote:
| This the reverse, actually, you can use much smaller
| inductors the higher the switching frequency. That's why the
| GaN chargers are so much smaller, for example.
| swayvil wrote:
| We had these flourescents in our computer lab at school. They
| were light yet dark. On yet off. Crazy. Some weird color or
| flickering frequency. If you sat there for a couple of hours you
| would start to stink. Like, a weird stink. Some speculated that
| it did something to your glands.
|
| Give me a nice candle.
| swayvil wrote:
| Hey it got flagged.
|
| Why do we use anonymity for that? What's gained and lost by that?
| edoceo wrote:
| I have LED in my home office. The "temperature" and this flicker
| were driving me bonkers. Fortunately no headache. Now I have them
| all pointed away to reflect off wall or ceiling, or behind
| diffusers. Much less bothersome,
| hinterlands wrote:
| I think this article is pretty confused.
|
| There are two ways to dim LEDs: linear regulation and some sort
| of pulse modulation. Linear regulation is wasteful and you're
| pretty unlikely to encounter it, especially in battery-powered
| devices such as phones or laptops. Pulse modulation is common.
|
| Human vision has a pretty limited response speed, so it seems
| pretty unlikely that PWM at a reasonable speed (hundreds of hertz
| to tens of kilohertz) can be directly perceived. That said, it
| can produce a stroboscopic effect, which makes motion look weird
| and may be disorienting in some situations. So I don't have a
| problem believing that it can cause headaches in predisposed
| individuals.
|
| You can dim your laptop screen in a darkened room and wave your
| hand in front. Chances are, you're gonna see some ghost images.
|
| Other than adjusting the frequency, pulse modulation can be
| "smoothed" in a couple of ways. White LEDs that contain phosphor
| will have an afterglow effect. Adding capacitors or inductors can
| help too, although it increases the overall cost. But that
| doesn't make the display "PWM-free", it just makes it flicker
| less.
| cosmic_cheese wrote:
| I think it's pretty common for people to be able to perceive
| PWM flicker in their peripheral vision that they can't when
| looking directly at the source. I encounter this fairly
| regularly myself.
| addaon wrote:
| > There are two ways to dim LEDs: linear regulation and some
| sort of pulse modulation. Linear regulation is wasteful and
| you're pretty unlikely to encounter it. Pulse modulation is
| common.
|
| Within the pulse modulation case, though, there are two
| important subcases. You can PWM a load that consists basically
| of just the LED itself, which acts as a resistive load, and
| will flash on and off at high rate (potentially too fast to be
| noticeable, as you say). But you can also PWM an LED load with
| an inductor added, converting the system into a (potentially
| open loop) buck converter. And this allows you to choose both
| the brightness ripple and the PWM frequency, not just have 100%
| ripple. Taking ripple down to 5%, or 1%, or less, is perfectly
| straightforward... but inductors are expensive, and large, so
| shortcuts are taken.
| phkahler wrote:
| Higher PWM frequency will let you use smaller inductors.
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