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

https://caseorganic.medium.com/the-invisible-light-thats-harming-our-health-and-how-we-can-light-things-better-d3916de90521

by SLHamlet • 1 year ago

169 278 1 year ago

caseorganic.medium.com

mtalantikite6• 1 year ago

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.

igor472• 1 year ago

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/

PaulHoule3• 1 year ago

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.

mtalantikite6• 1 year ago

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.

Saris4• 1 year ago

You can also eliminate flicker by not using PWM, and instead using a high switching frequency DC power supply with a clean stable output current.

Obviously it costs more, but I wish manufacturers would just do it.

bayindirh7• 1 year ago

Personally, I don't care for more energy efficiency if my head is hurting after 30 minutes under that light. I can really see all the flickering when I blink or move my head.

Similarly, I prefer a Class A amplifier if I have the space, but I won't open that can of worms here.

Workaccount22• 1 year ago

Old dimmers are triac based, with the potentiometer simply setting the trigger voltage, not doing the actual dimming. These were in fact very efficient.

JKCalhoun2• 1 year ago

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.

genewitch3• 1 year ago

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".

oakwhiz• 1 year ago

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.

bayindirh7• 1 year ago

Philips' Eye Comfort series virtually have no flicker. I personally only use these series. They come in CRI>80 and CRI>90 variants. Latter one is also dimmable and comes with soft on/off.

They are nice.

mousethatroared3• 1 year ago

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.

Zak7• 1 year ago

I totally can tell the reds are off.

How do the reds look to you?

I looked at the photometric reports from a couple Waveform models on their website and the R9 (saturated red rendering) was in the 90s for both with tint almost exactly on the blackbody line. The 2700K did have a bit worse R9 than the 4000K so I could imagine it doesn't look exactly like an incandescent.

mtalantikite6• 1 year ago

I mean I hate to be like "vibes", but, kinda vibes. There's just something about the light coming out of the Waveform LED I have in one lamp in my living room versus the incandescent I have on the other side of the room. Definitely not a scientific take!

I did at one point randomly put the LED in different configurations when I first got it and my wife was able to pick out which lamp had the LED in it every time. They just have a different feel, even if the temperature rating is around the same as the incandescent and the R9 was the highest of the LEDs I evaluated. At least these Waveform LEDs don't give me migraines though.

winrid3• 1 year ago

I have your problem. Philips makes no flicker LEDs, they don't have PWM like the Hue system, and good capacitors so no 60hz flicker. They're the "Ultra Definition Eye Comfort" models.

dotancohen2• 1 year ago

On older LEDs you could replace the caps, but newer ones use SMT caps that require more than just a soldering iron. It makes a huge difference, and also eliminates the slight delay when switching the lamp on (though I don't recall experiencing this with recent LED lamps, even cheap ones).

bondarchuk• 1 year ago

EyeComfort& LEDs have a high Colour Rendering Index, meaning that your home's furnishings appear in high definition and true colour.

What is this world coming to, that you have to buy some top-range lamps just to see the inside of your own home in true colour...

veltas• 1 year ago

I drive rarely, but the oncoming headlights are blinding when I do.

I drive a shallow car with old lights, and once I was blocked on a street by a much taller car sitting in front of me with very bright LED lights, and I couldn't see a thing because of the glare. I was unable to manoeuvre out the way because of this. They sat there for a minute or so stubbornly refusing to move for me before finally moving out the way.

Loughla• 1 year ago

It's super common where I live for teenagers who drive jacked up trucks to replace their headlights with super bright led lights. They don't adjust the angle of the beam, so they're just like brights all the time. It's miserable.

BoxOfRain2• 1 year ago

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.

What I miss are the old low-pressure sodium street lights that used to be ubiquitous in the UK. Not everyone's cup of tea but they were highly efficient (outperforming LEDs for a surprisingly long time) and had this cool property of being so monochromatic they ate the colours out of everything. This made them useful for astronomers because their light was easily filtered, and reduced their impact on wildlife relative to harsh blueish LEDs. The main reason I like them is aesthetic though, they made night look like night rather than a poor approximation of day.

Thankfully my local area have given up trying to use the really harsh white they put in initially, and have at least starting putting in warmer LEDs.

xattt• 1 year ago

Sodium light story: my family went to Niagara Falls and took a tour of the tunnels behind the falls. The tunnels were lit by sodium lights that were not augmented by phosphors.

It was so monochromatic that we thought we lost our shuttle bus stickers that were stuck to our shirts, and would have to walk around instead of being able to hop-on/hop-off. What a relief it was to emerge in daylight.

albrewer• 1 year ago

This made them useful for astronomers because their light was easily filtered

The wavelength is so specific that it can have all kinds of cool applications:

https://youtu.be/UQuIVsNzqDk?si=R4VUDCfC6zcHd4XC

zzo38computer4• 1 year ago

I did not know those things about the sodium lights, but I did think they were better than the LEDs which are too bright and have other problems. However, I think that they should not put so much light outside in the night time, anyways.

christophilus• 1 year ago

I don’t heave the migraines, but everything else you described is spot on. Sitting outside at night is much less enjoyable due to neighborhood LED lighting. If I could, I’d shoot them all out.

jollyllama3• 1 year ago

There is hope: https://www.congress.gov/bill/119th-congress/house-bill/3341

kstrauser• 1 year ago

That’s horrid. I can’t imagine going back to crappy incandescent bulbs today. We don’t need to import more disposable junk.

vitaflo10• 1 year ago

I have the same issues. I actually had to return an iPhone because the oled screens they use are so bad and gave me migraines.

For bulbs tho I found this site that tests tons of them for flicker.

https://flickeralliance.org/

It was a godsend and I was able to get some Ikea bulbs with zero flicker and they’ve been great. So at least my house isn’t a flickering mess. Now I just gotta figure out a phone that’s not garbage.

prmph• 1 year ago

Does this also affect Macbooks?

cycomanic• 1 year ago

How did you survive office buildings, airports, department stores etc. prior to leds? I am by no means sensitive to flicker, but fluorescent tubes which were used in pretty much every office building/large department store, before leds became common, used to flicker like crazy in comparison. And there was always at least one which was broken and flickered on and off very slowly (including the characteristic sound).

yx827ha3• 1 year ago

Thanks for the link! I bought a moto g power 5G - 2024. It has an LED screen. I've been using this line of phone for years. It's morning fancy, but at least I can actually look at it.

yx827ha3• 1 year ago

If you are sensitive, I would recommend getting an Opple Light Master. It's a tiny and cheap flicker meter.

mdip2• 1 year ago

Right there with you. I just dropped an amount of money I'm unwilling to admit on replacement bulbs throughout -- only this time I was replacing WiFi RGBW LED bulbs in rooms that had lower-end bulbs (almost everything on the market).

Incidentally, I went with LIFX -- I had purchased their bulbs back when they were the only realistic option besides Philips Hue for smart RGBW bulbs[0]. Still seems those two brands produce the most flicker-free variety.

[0] LIFX was a handful of lumens brighter at the time and didn't have a hub requirement

Melatonic• 1 year ago

You need high CRI lighting - that's the key to proper colors.

hedora• 1 year ago

The worst led bulbs I’ve ever seen were some overpriced name brand known for smart bulbs (probably philips). It physically hurt to be in the same room with them. My guess is that they forgot an IR or UV filter or something.

Hyperikon used to make great, somewhat cheap bulbs, but went under during the pandemic.

These days, I just get cheap 3000K, 90+CRI ones at the hardware store, and they’re fine.

Watch out for idiocy like “smart” bulbs though. For instance, they have ones that change color temp if you rapidly flip the light switch on and off and back on.

Also, make sure they are dimmer compatible. The ones that are not flicker badly (even at full brightness on our dimmers) and burn out after a few years.

W3zzy• 1 year ago

People just don't pay attention to colour temperature. Warm LED lights should be more common in stead of those filthy blue LED's

JKCalhoun2• 1 year ago

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• 1 year ago

You can in fact dim leds. You can see a lot of controllers that are just that at various parts suppliers.

genewitch3• 1 year ago

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.

mrob5• 1 year ago

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).

Kirby648• 1 year ago

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.

PaulHoule3• 1 year ago

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...

mrheosuper2• 1 year ago

it's expensive, and in some way, less efficient.

It takes 1 mosfet to turn led on/off from a MCU GPIO, but if you want to do DC dimming, now you have to either add more passive components, or turn to special IC, both cost more.

normie3000• 1 year ago

Do computer screens flicker and release this bad light?

igor472• 1 year ago

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• 1 year ago

Some do, some don't. Sites like notebookcheck.net typically mention in their reviews whether a given laptop screen exhibits PWM.

layer8• 1 year ago

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.

leakycap15• 1 year ago

Yes-many do.

It's difficult for PWM-sensitive Mac users right now, as the majority of Apple devices for years have had rough PWM and of course there is no hardware alternative.

I'm stuck on a MacBook from years ago because the only current MacBook I can buy is the Air line, which I'll probably buy soon to replace my aging 2018 MacBook.

No currently for sale iPhone is PWM-free. The iPhone 11 (non-Pro) was the last mainstream device Apple made with a PWM-free backlight. The SE 3 (2022) was also PWM-free, but is no longer available from Apple beyond what stock is still around.

blacksmith_tb• 1 year ago

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• 1 year ago

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.

demosthanos14• 1 year ago

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.

_3yjt10• 1 year ago

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.

demosthanos14• 1 year ago

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.

wasabi991011• 1 year ago

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.

mrob5• 1 year ago

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.

demosthanos14• 1 year ago

If the article said "I find PWM annoying" I wouldn't have commented like I did.

loph• 1 year ago

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• 1 year ago

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.

Zak7• 1 year ago

even the simplest ones strobe

The simplest LED sources running from AC mains power strobe at mains frequency, which is very visible and very annoying.

Fancy LED sources don't strobe at all. I'm using an LED panel intended for videography as a room light; any flickering could show up as scanlines in video, so most lights intended for that purpose are flicker-free.

Jazgot• 1 year ago

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.

leakycap15• 1 year ago

Science is informed by listening to the experience of other humans and doing research.

PWM sensitivity is real and has nothing to do with someone's belief system.

orwin• 1 year ago

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

satiated_grue• 1 year ago

"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.

mrob5• 1 year ago

I've seen this repeated many times but never seem any evidence for it. At typical PWM frequencies the perceived brightness is just the average brightness of the wave. I believe this myth arose from people driving low-brightness indicator LEDs using PWM for increased efficiency when using simple current-limiting resistor circuits. People saw the energy savings from less waste heat in the resistor and somehow confused it with something happening in the eye.

SLHamlet• 1 year ago

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."

cwillu2• 1 year ago

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• 1 year ago

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.

hobs• 1 year ago

Then congrats, you don't have the problem because to those of us who can notice it, PWM working this way is pretty obvious from first principles.

swayvil2• 1 year ago

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.

swayvil2• 1 year ago

Hey it got flagged.

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

edoceo• 1 year ago

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,

leakycap15• 1 year ago

Lightbulbs are cheap & eyes/brains are not... home office? May be worth taking care of yourself and save these cheap bulbs for places you don't spent most of your waking hours.

hinterlands• 1 year ago

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• 1 year ago

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.

bongodongobob• 1 year ago

Nah, LED lighting generally uses at least 200 Hz at a minimum. Some up to kHz. You can't perceive that. Older stuff or cheap quality might be using un-rectified AC/DC which you can see. Like cheap Xmas lights.

addaon2• 1 year ago

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• 1 year ago

Higher PWM frequency will let you use smaller inductors.

rowanG077• 1 year ago

I personally doubt PWM is visible at all at high enough speeds (kilohertz+) even in peripheral vision. I would love to see a good study on this.

stodor89• 1 year ago

I can't see PWM flickering even at 30Hz. But it gives me bloodshot, twitching eyes even at 20kHz.

Zak7• 1 year ago

Hi there, flashlight nerd here.

There's a third way: a switched-mode power supply with regulated output current. This is used in most better-designed flashlights (which doesn't always correlate to price) and can be used by anything else that needs to drive an LED as well.

The article doesn't discuss what technique should be used for "constant current reduction"; it probably shouldn't be a linear regulator where efficiency is a priority.

PWM is less annoying if the frequency is very high (several kHz), though I'll leave it to people who research the topic to speak to health effects.

wrs2• 1 year ago

In the world of LEDs, a switched-mode power supply with regulated output current is called a "constant current driver". I assume that's what this calls "DC dimming".

demosthanos14• 1 year ago

The article is worse than confused. It's a marketing piece written in a way that sounds vaguely science-y but with only a tenuous basis in real research.

I wrote more here: https://news.ycombinator.com/item?id=44312224

entropie2• 1 year ago

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.

I (and it seems others too) are very interested in this topic. I would appreciate if you could write an aritcle with "less confusion" so I can save it in my tumblog for future reference.

mousethatroared3• 1 year ago

Even if your PWM is faster than your eye's response it's trivial to see how one is still affected, namely, the stop motion effect.

That effectively lowers the frequency of the lcd.

rcxdude• 1 year ago

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.

The other reason is LED brightness and color is quite non-linear with current, so PWM gives a much more straightforward dim than adjusting a current smoothly.

klysm• 1 year ago

PWM is not to be confused with Switch Mode Power Supplies in the general case

winrid3• 1 year ago

It causes physical pain for many. You can't always see the flicker but your eye muscles react faster than your perception, and they get sore.

I had to get rid of a Samsung TV (120hz backlight, replaced with linear dimmed Sony, nicer anyway..) due to this, and I can only use modern phones at 100% brightness which disables PWM.

When I moved into my current residence I couldn't figure out why my eyes were always sore. I realized my landlord put in cheap LED can lights. I swapped them out for nicer ones, pain gone. People need to stop being cheap AF.

leakycap15• 1 year ago

It makes me wonder how differently we all perceive the world around us, and if that impacts our decisions in more ways than we realize.

I've had to drastically change my devices after learning PWM was causing my vision issues and eye pain. My partner has no issues using those same devices.

xeonmc• 1 year ago

I wonder if it’s possible to have randomized sub-cycle interval variation so as to “spread out the spectrum” of the PWM signal while preserving the same resulting integrated brightness over the observable timescale.

Basically like how Apple laptop fans work, but for temporal modulation of signal instead of spatial modulation of fan blade gaps.

lightedman6• 1 year ago

"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."

I make power drivers. I have this ultra-tiny one, with output scope captures. It produces ~825kHz PWM output, single-digit mV and mA ripple, 94+% efficiency depending on input voltage (output is input minus 0.2V)

I can induce sacchades in my eyes at will and at high speeds. Couple that with waving my hand in front of my face as I do that, and add in human vision persistence, and I can get artifacting that reveals flicker even at that high of a rate of PWM. Only direct battery power fails to induce that artifacting effect in my vision when I do that combination of movement.

lightedman6• 1 year ago

There are other ways to dim LEDs. Voltage stepping to control how much current can actually flow through the diode is one method (and this is how we test LEDs where I work, a 3V LED gets tested at ~2.4-2.6V. It will barely draw a couple milliamps despite the power supply set to allow an amp of draw.) The LED will light up, enough to see that it is working well, but not eye-searingly bright.

Kirby648• 1 year ago

Voltage control of LEDs is extremely unreliable. The amount of current consumed at a specific voltage will vary wildly depending on temperature, process, etc. Nobody does voltage control for LEDs unless you do not care about consistent brightness at all.

mrheosuper2• 1 year ago

no, 2 main methods to change led brightness: Changing duty cycle, or changing current. PWM is way to change duty cycle, and Linear is 1 way to change current. There are other ways to change duty cycle or current.

Roguelazer• 1 year ago

*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)

mouse_• 1 year ago

thanks for saving me time

neltnerb• 1 year ago

I tried my best but once it starts citing different sources as providing hard numbers and then not linking to the sources... and of course they're selling something. Might need a citation on that claim that iPhones don't use PWM.

nntwozz• 1 year ago

iPhone 16 Pro Screen flickering / PWM detected 239 Hz Amplitude: 15 %

https://www.notebookcheck.net/Apple-iPhone-16-Pro-smartphone...

The frequency of 239 Hz is relatively low, so sensitive users will likely notice flickering and experience eyestrain at the stated brightness setting and below.

There are reports that some users are still sensitive to PWM at 500 Hz and above, so be aware.

I always check notebookcheck.net for PWM stats.

For reference, the regular iPhone 16:

Screen flickering / PWM detected 60 Hz Amplitude: 25.75 % Secondary Frequency: 487 Hz

culopatin• 1 year ago

Even if the iPhone was flicker free, holding the iPhone itself throws all that out the window with all the addictive colors and notifications and badges

vitaflo10• 1 year ago

I had to return an iPhone because the oleds they use flicker so bad. The only iPhones that don’t ficker are the SEs because they use ond school LCD screens. But of course they got rid of the SE. So now I’m stuck on this old SE3 until I can find a different phone that doesn’t flicker because as of now ALL iPhones flicker.

mousethatroared3• 1 year ago

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.

vitaflo10• 1 year ago

I have a phone camera app you can set the shutter speed to 10000 fps. It becomes super obvious then, and you can actually somewhat compare how fast the flicker is that way.

shanemhansen• 1 year ago

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?

jeroenhd• 1 year ago

Car headlights seem to really cheapen out on the PWN flicker. Even the 2 euro LEDs I buy at the discount store seem less flickery than the lights of some luxury cars. I thought it could be that people are buying the cheapest replacement bulbs they can get their hands on, but then I saw the same thing happening on a new BMW.

I also believe some people are just more affected by flicker than others. Some get headaches or migraines from working under PWM light, others don't even notice.

I'm not a mechanic, but I believe these car lights are capable of achieving some pretty high brightness (necessary for fog lights etc.) but are dimmed under normal conditions, leading to PWM effects you also see in cheap dimmable bulbs. It's especially noticeable for me on those "fancy" lights that try to evade blinding other cars (and end up blinding bikes and pedestrians) and those animating blinker/brake light setups.

denkmoon• 1 year ago

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.

g-b-r• 1 year ago

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?

mrob5• 1 year ago

I don't think this is true. The typical uneven LED spectrum causes poor color rendering accuracy, but human color perception is highly inconsistent anyway. Think of the blue/white dress people were arguing about ( https://en.wikipedia.org/wiki/The_dress )

vitaflo10• 1 year ago

It can be both, but for people sensitive to PWM, it’s the PWM.

djmips• 1 year ago

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

mikeytown2• 1 year ago

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

trinix9122• 1 year ago

Wouldn't it surpass the flicker if you're recording at 60fps and the lights flicker at a multiple of that (ex. 120Hz in the USA)? At least that's my experience recording CRT monitors - you set it to a multiple of its refresh rate and the flicker is gone from the video.

rda2• 1 year ago

I used this method to check some of the lights in my house a few years ago. The slow-mo video mode on my phone used a rolling shutter which captures one row of pixels at a time, meaning you could see the flicker in part of the video, even when it’s a multiple of 60 Hz or above 240 Hz. The flicker and camera frequencies also aren’t exactly synced up, so you can see the dimmed parts move across the screen.

You can get a pretty good idea of frequency, depth of flicker, and if the LED’s colors are flickering in sync from this, and I can confirm that Philips LEDs, specifically the EyeComfort series, are good.

voidUpdate2• 1 year ago

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

kazinator2• 1 year ago

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.

kazinator2• 1 year ago

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

julik• 1 year ago

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

b1123• 1 year ago

Let's take a bulb, and instead of one led we have 10 less powerful leds in one package.

Now you can turn off leds one at a time, have 1/10th dimming, and no pwm.

The same could be done with LCD backlighting or edge lighting on displays. Additional complexity, to be sure, but no power loss.

OLED is, well.. oled. Not sure what to do there.

4gotunameagain2• 1 year ago

Except that perceived illumination is log, not linear ;)

amelius• 1 year ago

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

spiffyk• 1 year ago

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.

sitharus2• 1 year ago

Yes it absolutely is. Those are candle-style bulbs that use filament LEDs, they’re normally just use a basic rectifier and a regulator chip that does basic linear regulation of the peak of the sine wave.

They flicker at 100Hz due to the rectification (or 120hz in those 60hz countries of course).

Dimmable bulbs use higher frequencies.

mortenjorck• 1 year ago

There is a pendant light in my entryway that came outfitted with LED filament bulbs when I bought my home. They flicker noticeably, and I would have replaced them all if it were in my living room.

One of the bulbs recently burned out, and I picked up a replacement at Menards. Even though it was just a basic Sylvania, the new one clearly has a rectifier circuit as it does not exhibit any flickering that I can detect.

So anecdotally at least, the cheap bulbs without rectifiers seem to be going away from the big box stores (although I’m sure you can still get them with unpronounceable all-caps names from Amazon).

user_78323• 1 year ago

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.

It is done because, like most crappy things in the world, it saves somebody, somewhere, a few cents on the dollar.

Most people would not be able to tell the CRI impact of DC dimming vs PWM. Many do not visibly notice the difference. (I unfortunately do, and you won’t believe how many expensive Mercedes and similar cars flicker).

But high frequency PWM is slightly more difficult and expensive, and DC dimming might need a few more capacitors or inductors… so let’s save a buck there, shall we?

user_78323• 1 year ago

Kinda odd, but why was this downvoted? Was anything wrong (or even unpopular)?

RyJones• 1 year ago

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

fortran77• 1 year ago

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)

vitaflo10• 1 year ago

Im a ham radio op and incredibly sensitive to PWM lighting. Imagine how I feel!

At least my house has little RFI. My neighbors on the other hand…

scheeseman486• 1 year ago

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.

monster_truck• 1 year ago

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

gblargg2• 1 year ago

Even incandescent running on AC has flicker. It's funny when that's used as the gold standard. LED running on DC has less flicker than normal incandescent.

quesera• 1 year ago

An LED running on continuous DC has no flicker, but PWM is not continuous DC, it's a square wave of some frequency.

Incandescents have analog inertia in the filament which smooths the light output from the AC sine wave. This smoothing is not 100%, but I've never met anyone who can detect it without equipment.

A photocell and an oscilloscope will show the smoothed live-frequency wave (I wouldn't call it a "flicker"). The wave delta is relatively higher in the perceptual range as the voltage is lowered to approach the minimum "glow-activation" threshold of the filament -- i.e. the fluctuation is more noticeable when the bulb is dimmed to nearly off.

dinkblam• 1 year ago

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?

throwaway2902• 1 year ago

Random guess here but maybe some phase interaction with electrical grid frequency

vitaflo10• 1 year ago

I have massive issues with PWM and used this site to decide on what bulbs to buy.

https://flickeralliance.org/

It was a godsend. In I went with a bunch of Ikea bulbs and couldn’t be happier. Absolutely zero flicker in my testing, good color output.

qiine• 1 year ago

after searching for a while I found osram to make light-bulb that I could support:

https://www.amazon.fr/dp/B073QS6K3C?ref=ppx_pop_dt_b_product...

Daisywh• 1 year ago

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.

DrNosferatu4• 1 year ago

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

DrNosferatu4• 1 year ago

I guess not at the circuit level because the higher peak signals are necessary to drive the light emission?

Anyone care to weigh in on this?

davrosthedalek2• 1 year ago

You totally can, but the target quantity is average current, not average voltage. Since the LED is a diode, that's not the same.

DrNosferatu4• 1 year ago

In the meantime, it occurred to me PWM stimulate a light-emiting phosphor for continuous-time ambient light applications - CRT style.

Liftyee• 1 year ago

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

leakycap15• 1 year ago

I'm interested in this topic and stay on top of most threads/discussions about PWM.

I doubt there are any long-term effects of it.

I would have thought the same, but it seems to be a common experience that once someone becomes PWM sensitive it actually sticks with them.

I've been a techy my whole life; the iPhone 12 mini seemed to be the device that triggered my PWM sensitivity and since then I have been extremely sensitive to any device with PWM.

Although I have tried to keep PWM devices out of my life, I can still quickly tell when the TV in a lobby or the airplane entertainment display has PWM and there's not much you can do about it.

_spduchamp• 1 year ago

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.

perching_aix• 1 year ago

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.

mdip2• 1 year ago

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.

leakycap15• 1 year ago

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.

atmanactive• 1 year ago

Would you please care to elaborate? How can you tell? Which eye issues? Thanks.

leakycap15• 1 year ago

It makes my eyes physically hurt, to where I can't think or focus on anything. It feels as if my eye is up next to the screen of a window and just touching it.

Not all PWM has issues: I have an LG Plasma TV and it has PWM, but the way the plasma glows compared to the rigid on/off PWM cycling on modern iPhones means the Plasma display causes no issues. Same with Samsung Note9, which uses OLED with a soft PWM ... no issues

thePhytochemist• 1 year ago

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!

ajb• 1 year ago

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.

zzo38computer4• 1 year ago

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.

t0bia_s• 1 year ago

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.

matt-attack• 1 year ago

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.

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

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