from Hacker News

PWM flicker: Invisible light that's harming our health?

by SLHamlet on 6/18/25, 5:32 PM with 277 comments

• by mtalantikite on 6/18/25, 6:08 PM

  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.

• by hinterlands on 6/18/25, 10:03 PM

  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.

• by spiffyk on 6/19/25, 10:04 AM

  Isn't this article conflating PWM flicker with cheap AC rectifiers causing LEDs to flicker because they periodically, at 50 Hz, get under the voltage they need to emit any light? I can't see why light fixtures in buildings—except modern ones where the lights are actually dimmable—would even have any sort of PWM.

• by shanemhansen on 6/18/25, 11:15 PM

  I've wondered about PWM flicker when I started trying to figure out why so many modern car headlights seem like they are strobing to me.

  Initially I thought it might be related to the alternator.

  I still don't know why I perceive these headlights as having an annoying flicker or why. I'd love it if some (informed) commenter could clear it up for me. Am I imagining it?

• by loph on 6/18/25, 6:31 PM

  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?

• by voidUpdate on 6/19/25, 8:06 AM

  I can sometimes tell when a lamp is PWM'd if I look out it out of the corner of my eye. I suspect it may just be the cheaper, lower frequency ones but I can often see it flickering, such as a particular lamp I have when it's on low brightness, and there's a particular shop near me that I can see it in

• by julik on 6/19/25, 8:57 AM

  As a flicker-sensitive person: the sad part of it is that to do this properly you need to have your LEDs on a proper inverter, so for most scenarios getting rid of the flicker means "get expensive light fixtures _and_ rewire their supply _and_ you can't use your existing AC mains anymore, nor can you use switches". The PWM is a cheap way to do dimming given the AC input of the grid. And it will be especially prevalent when you do want LEDs but you don't want to "do anything special" to make them work well

• by thePhytochemist on 6/19/25, 8:29 PM

  This is a timely article for me since I'm building an indoor light display and the client specifically mentioned flicker. It's supposed to be a cosy warm light setup (that animates to show the movement of our planets, each represented by a lantern in the building). They were so concerned about flicker they suggested using incandescent but I'd really like to use leds for the obvious reasons (power consumption, fire risk, lifetime, color choice).

  What I chose is an ESP32 controller attached to WS1812B LEDs. It turns out these operate at a PWM of nearly 20Khz and my low key tests confirm this. Even at the lowest dim level I can't detect any flicker when I move the led quickly or move something quickly in front of it.

  It's amazing to me that you can get off the shelf hardware with WLED installed that works at 20Khz with these cheap RGB LEDs for less than the leading brands like a Philips Hue!

• by orwin on 6/18/25, 7:27 PM

  I flagged because this is a submarine ad, but it was still interesting tbh.

• by swayvil on 6/18/25, 9:11 PM

  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.

• by mdip on 6/19/25, 2:59 PM

  They list the PWM frequency in the bulb specifications? That's news to me.

  A few months ago I went through most of the bulbs in my house and replaced nearly all of them with LIFX bulbs. I had spent quite some time trying to figure out which bulbs would have the least flicker and knew from my more DIY setups[0] that PWM frequency is the cause.

  I deal with Migraine somewhat regularly and PWM flicker/strobe lights amplify the pain when I'm dealing with one.

  Nearly every smart bulb I've grabbed incorporates such a miserably slow PWM setting that dimming the bulb to 1% results in lighting that's reduced by only about 25%. It becomes clear when you set it to 1% that the manufacturer couldn't limit length of the "off" cycle further or the bulb would begin resembling a strobe light.

  I haven't tested all of the more expensive variants, but I also had a really hard time finding any "from the manufacturer" information about the PWM frequencies. I've also never encountered an incandescent drop-in that uses anything other than PWM frequency (I wasn't even aware that there are fixtures that do that).

  [0] Experiments? Magic-smoke generators? Sometimes-almost-house-fires? I'm no electrical engineer.

• by mousethatroared on 6/18/25, 11:00 PM

  An easy way to see PWM flicker (and distinguish cheap led bulbs for better ones) is to wave your open hand in-front of them.

  If you see the strobe effect, return the bulb and buy another one.

• by monster_truck on 6/19/25, 11:35 AM

  I thought this article was a parody of the people who think they're being poisoned by wifi until I read the comments here.

  I started looking into it, these poor people are paying hundreds of dollars for "flicker measurement" devices that cannot reliably tell you how the light source you're measuring is controlled

• by denkmoon on 6/18/25, 11:36 PM

  Entirely anecdotal and just personal experience but I get eye strain and headaches from "flickery" LEDs. Cheap shitty room lights. Replace them with good bulbs (Philips Hue) which strobe at a much faster rate and hey less eye strain and less headaches.

  I also just hate hate hate seeing the flicker in my peripheral vision.

• by zzo38computer on 6/20/25, 1:42 AM

  I think there are many problems with LED general purpose lighting. They are too bright, wrong colours, and others. I prefer to have the windows that we can have the light from the sun outside, and when that won't do, to use incandescent lights which are not too bright. However, not everyone will do that, and they put too much light outside at night too.

  LED does have uses, such as many indicator lights (although they should not make them blue (unless you already used the other colours); but blue indicator lights are too common), and for some kind of displays. I think LED is not very good for general lighting, Christmas light, etc.

• by perching_aix on 6/19/25, 2:11 PM

  I don't know about the health risks and harms, but it sure as hell is annoying if nothing else. I don't think it's due to PWM specifically, but the light in my fridge strobes at the mains frequency, so it "samples" my arm as I move it around in there when picking stuff out. But 50 Hz is extremely low - so it looks like as if my arm's movement "stuttered". Super jarring.

  Not sensitive to this thankfully, so apart from making me act a diva and pissing me off, it doesn't affect me, but I sure wish I understood the EE side of it all so that I could properly avoid all these lights, at least in my own home.

• by normie3000 on 6/18/25, 6:25 PM

  Do computer screens flicker and release this bad light?

• by edoceo on 6/18/25, 9:56 PM

  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,

• by JKCalhoun on 6/18/25, 6:24 PM

  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.

• by kazinator on 6/19/25, 8:17 AM

  > The light wasn’t steady; the LEDs were flickering, pulsing on and off thousands of times per second to create the dimmed effect.

  If it really is thousands, I don't think you have a problem.

• by matt-attack on 6/20/25, 3:56 PM

  I find it really bothers some, when I see it on new car, brake lights and nighttime running lights. As I dart my eyes back-and-forth, I can just plainly see the flicker. It’s such a shame that engineers don’t know how to select the right parts for these used cases. It makes the car look really cheap, and I’ve seen this on very expensive vehicles.

• by SLHamlet on 6/18/25, 8:55 PM

  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."

• by kazinator on 6/19/25, 8:20 AM

  Fun tangent.

  The 1981 film Looker, written and directed by Michael Crichton, features a trope: the Looker gun, which induces a trance in its targets via flashes of light, such that they are unaware of the passage of many hours of time.

  https://en.wikipedia.org/wiki/Looker

• by Roguelazer on 6/18/25, 11:00 PM

  > *Up to 15–50% slower decision-making in offices with high flicker (and high CO₂)

  just throws me right off the argument in an article when the fine print notes that a cited study is confounding the thing the author cares about ("sensitivty to flicker") with a much simpler and better-understood explanation (CO₂ poisoning)

• by t0bia_s on 6/20/25, 5:41 AM

  Utility frequency vary depending on location. That's why we have NTSC and PAL standards (50 vs 60 Hz) for flicker free video under various artificial light conditions.

  Second image is just interference with camera chip frequency. Usualy eliminated by mechanical shutter in photography.

• by ajb on 6/19/25, 10:54 PM

  I wonder if some of the problem may be "beating": the PWM frequency of two lights may be too high to affect anyone, but if they are different, then where they overlap you will see a pulse at the difference between the frequencies. Surely that would be a very obvious problem though.

• by leakycap on 6/19/25, 6:50 PM

  I'm still using a 2018 MBP & iPhone SE 3 because newer Apple devices make my eyes hurt for the rest of the day after a few hours of use.

  PWM is awful. I can tell within seconds of seeing a screen if it has PWM and usually I start to get eye issues within a few minutes.

• by mikeytown2 on 6/19/25, 7:38 AM

  Use your phones slow motion video to check flicker. Phillips has one of the better led bulbs out there

• by _spduchamp on 6/19/25, 1:59 PM

  Apparently dogs have a far higher flicker fusion threshold. So a light that might seem OK to you is like a disco stobe for your pooch.

  Also, if you take a photovoltaic cel and hook it up to an audio jack, you can turn the unseen flicker in light into sound.

• by Daisywh on 6/19/25, 12:39 PM

  We often talk about screen time and eye strain, but rarely do we mention the quality of ambient light. Low color rendering index, high flickering LED lights may not cause eye strain immediately, but they can wear on your eyes over time.

• by DrNosferatu on 6/19/25, 1:24 PM

  Can’t we low pass filter PWM ambient lights, to make them time-continuous?

• by g-b-r on 6/18/25, 11:39 PM

  I'm so surprised this hasn't been said yet.

  Isn't it extremely more likely that any problem with the appearance of something under LED light be due to the light's peculiar spectrum?

• by RyJones on 6/19/25, 10:42 AM

  You can also spot houses and cars with high dollar alarms and ir cameras. Under night vision they are very obvious. It’s like looking at a light show

• by Liftyee on 6/19/25, 1:43 PM

  With the lofty claims of "health risks", I was disappointed to find no sources linked at the bottom of this article (correct me if I'm wrong).

  Based on my personal experience, I think "health risk" is an overstatement: bad PWM can be uncomfortable (Geneva Airport had particularly egregious lights that started flickering in your peripheral vision), but I doubt there are any long-term effects of it.

  Reading further down, a few other comments [1][2] have stated this better than me.

  [1]: https://news.ycombinator.com/item?id=44313661 [2]: https://news.ycombinator.com/item?id=44312224

• by djmips on 6/19/25, 1:58 AM

  Is PWM kind of generic term now? There is also PDM ( pulse density modulation ) - might be a better way to modulate LED

• by blacksmith_tb on 6/18/25, 6:28 PM

  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%?

• by dinkblam on 6/19/25, 11:37 AM

  can anyone recommend flicker-free LEDs (E14) to order from Amazon.de?

  incidentally i found some LEDs to be extremely annoying but the flicker would sometimes just disappear on its own or after turning off and on the light switch. what could cause this?

• by amelius on 6/19/25, 9:09 AM

  It's better to filter your PWMs or use an inductance based chopper.

• by fortran77 on 6/19/25, 10:59 AM

  PWM lights generate a lot of radio frequency interference. Nobody seems to care except for us ham radio operators who can’t enjoy the radio anymore. (It’s also a reason we lost AM radios in cars)

• by Jazgot on 6/18/25, 6:38 PM

  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.

• by satiated_grue on 6/18/25, 7:34 PM

  "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.

• by scheeseman486 on 6/19/25, 11:28 AM

  The health stuff seems more like woo to me, but subjectively speaking for a while I had OnePlus phone with linear dimming it was easily the most pleasant to read at it's lowest brightness setting, while simultaneously being able to go even dimmer compared to any other phone I've ever used.

  The gamma curves got a bit messed up, but when it's that dim it's not like I expect stellar color accuracy anyway.

• by demosthanos on 6/18/25, 6:31 PM

  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.

• by swayvil on 6/18/25, 9:35 PM

  Hey it got flagged.

  Why do we use anonymity for that? What's gained and lost by that?