LED Strain
ledstrain.org
ledstrain.org
1. Lots of LEDs flicker. Shitty ones with twice the frequency of the main current (so 100/120 Hz) While you might not notice this it causes eye strain and can lead to eye fatigue, headaches, migraines.
2. Most LEDs have a low CRI (Color Rendering Index, or called Ra which is one standard to measure it), this means that they do not emit light in certain frequencies causing objects to look dull/gray. Most LED lamps have a Ra value of 80, meaning that they emit on average in the 80% of a spectrum that covers most of the visible light.
If you look around you'll be able to find reasonably priced LEDs with 90+ Ra and no flicker, but its a pain in the ass to research it. Especially if you need something more special like a LED light strip for your kitchen.
Edit: Incidentally every single bulb (15 of them) is still working too, we haven't had any issues with them failing.
http://www.lutron.com/en-US/Pages/LEDCompatibilityTool/Compa...
This is how we used to be able to measure speed of spinning objects too. :)
A lot of places use fluorescent lights which will look real weird if caught in the frame without some kind of flicker compensation just as one example so its pretty important.
There are x-rays of the LED here: https://www.chipworks.com/about-chipworks/overview/blog/true...
My first thought was: why don't they just filter the output? My guess is that perhaps LEDs are more efficient when being driven full ON or OFF rather than with a steady DC.
It's actually the opposite, efficiency goes down when current goes up.
That's with a full rectifier. It's even cheaper to go half-rectifier and end up with 50/60Hz flicker. Being cheaper, this happens a lot.
I'm super sensitive to this flickering and will get nausea after sitting in some cheap LED lighting while other people hardly seem to notice.
I jokingly say that with cheap 50Hz LED lighting and 60fps screens, virtual reality now has a higher frame rate than real reality.
White tubes are made of a mixture of phosphors, and each of them has a different time constant, meaning the flickering is noticeable as repeated changing of colors. Take a photograph (with a rolling shutter phone for example) of a fast moving object under fluorescent light and you'll see blue and yellow shadows from the changing light[1].
[1]: https://photo.stackexchange.com/questions/60701/why-do-i-get...
Is it just a matter of adding a bridge rectifier? I guess I'd need to add some resistors in there also to dim the emitters since they'll be on twice as often (to prevent premature burn-out).
Has anybody looked into this? I'll admit to being a bit eccentric.
No, the diodes don't, the drivers do. You are speaking to a technical audience ;)
> means that they do not emit light in certain frequencies causing objects to look dull/gray. Most LED lamps have a Ra value of 80, meaning that they emit on average in the 80% ...
Hardly. It means that they reproduce a set of 8 or 16 fixed frequencies from the ral pallete. It doesn't cover anything inbetween so it's just a rough rule of thumb. It doesn't cover colors in the far red (or was that violette on the other end of the soecteum?) at all.
Overall, overexposure of some frequencies, arguably to appear brighter and fuller, has damaged musuem pieces--Radiation stress, really. All they can do now is individual tests with photometric instruments, because they can't trust CRI. Same for horticultural lighting, which hasn't really taken of anyway.
Edit: Some manufacturers publish reference curves in the datasheets for their emitters, however I don't know how accurate these are under varying conditions and across batches.
[1] See e.g. https://ocw.mit.edu/courses/electrical-engineering-and-compu...
https://lavinia.as.arizona.edu/~mhammer/outreach/cdSpectrome...
(diffraction spectrometer from used CD/DVDs, very easy to make, and it costs ~$0)
Electrons in molecules have discrete energy states they can occupy, per quantum mechanics (the discrete set of wafunction solutions)[1]. Consequently they can only transition between states by absorbing or emitting photons of specific energy values (I believe it doesn't have to be exact due to scattering and various QED dynamics, but it has to be very precise). If your molecule is exposed to broadband light, a few photons will match those ionization energies, however the quantity should be small[2]. If your light source contains peaks though, and there happens to be important molecules whose energy transition matches your source (a big if), you're going to get a lot of ionization.
I should have mentioned a more established issue is fluorescent lamps emit more blue/violet and UV than LEDs (LEDs are usually packaged in plastic anyways, so even if the emitted there'd be no risk of uv exposure). In common molecules the more prevalent ionization energies are UV and beyond, that's why the risk is greater.[3]
[1] https://en.wikipedia.org/wiki/Energy_level
Electron states are central to molecular dynamics and chemistry.
[2] Infinitesimal ideally, just small in reality because of tolerances as mentioned
[3] https://en.wikipedia.org/wiki/Fluorescent_lamps_and_health#U...
https://www.scientificamerican.com/article/can-compact-fluor...
Plants are known to have been "burned" by LED, and not due to heat. Some turn pale if they don't get a broad spectrum, if I remember correctly.
I've seen 'drivers' that are nothing more than a resistor in series with the LED. So the LED, acting as a half-wave rectifier, causes the flicker. To your point, in this case the LED should be considered part of the driver.
Pulse width modulation. ;)
On the other hand, I have not seen a light source with low CRI that looked good illuminating people, natural materials, or anything else where subtle differences in color are relevant.
I'm wondering how annoying those might be for a dog.
For people in North America, I'd recommend https://www.hyperikon.com/ for LED products from screw-in bulbs to large area lights with high CRI and no flicker (note: a few products don't have high CRI, so do check the product page). They offer a good range of color temperatures too.
> Most LED lamps have a Ra value of 80, meaning that they emit on average in the 80% of a spectrum that covers most of the visible light.
That's not what Ra means. It's not a percentage - in fact, something with a perfectly flat distribution covering all the visible spectrum would not have especially high CRI, because that's significantly different from the spectrum of blackbody radiation, on which CRI is based. The actual algorithm for calculating CRI doesn't fit nicely in a comment, but it's in the Wikipedia page: https://en.wikipedia.org/wiki/Color_rendering_index
Edit: missed the negation - CRI is not high for a perfectly flat spectrum.
This comment alleviated some of creeping anxiety from the above posts that I maybe hadn't done enough research (I hadn't, I just got lucky).
Old HN thread about the iOS app: https://news.ycombinator.com/item?id=14023196
On the other hand, if you're looking for IoT light bulbs, their Tradfri system is a lot cheaper than Hue and I've read that their gateway has reasonable security practices and a good API. I would bet that those are more premium products that they wouldn't have released without making sure the electronics are quiet.
LED or CFL? The latest batch of LED's they've only had about a year, the phosphors were switched around in their 1000 lumen (lm) and 1600lm E26 bulbs. They also advertise 100lm/W.
These are not the junky dirt cheap 80lm/W 60W (800lm) equiv bulbs that you can pick up everywhere now (and I don't recommend for lighting a room).
Also, watch for open boxes, I bought ~$200 in bulbs last time and one of the globe bulbs I bought was an obvious return and did not work.
LEDs do not have to flicker, but supplying low-ripple, constant-current DC power is not as cheap as ways of powering LEDs that do result in flicker.
Problem is not everyone have this problem. I have this what I call latency intolerance syndrome.
I am on a mission to make lighting healthy. That's why I made Bedtime Bulb: https://bedtimebulb.com/ It has the lowest flicker I've ever seen in a bulb form factor—even less than those claiming to be "flicker-free."
If you're in Canada, try this link: https://www.amazon.ca/gp/product/B07H49N46N
Let me know if you're still having trouble. Thanks!
However, once place where I do notice it and it's annoying is with taillights on some cars - sometimes when I sweep my eyes across the cars ahead, I see the strobe effect from LED taillights.
It doesn't seem to happen with all cars.
I've noticed it in a few bike taillights, but not nearly as much as in cars. I used to have an early LED bike headlight, and the strobing was very apparent when the light was dimmmed, I could only use it at its highest level.
I'm pretty sure the DOT requires that your headlights don't blink, so I wonder how low the PWM frequency can be until they consider it blinking?
I also wonder whether they do it on purpose. How hard would it be to run the PWM at a few kHz instead of the < 100 Hz frequency it seems like they're using?
kHz? Really? That seems very high to me.
In general, light is linear and time invariant. That means in a flickering light system, a flicker of blue light then of red light, or red and blue at the same time, are indistinguishable if the 'sampling' system doesn't have sufficient bandwidth to resolve the flicker at all.
There do exist nonlinear optical components[1], but none that exhibit nonlinearities at the light intensities you'll find at home!
Additionally, even if the above were not true, flickering LED sources tend to flicker at a multiple of the AC supply, so it's very unlikely you'd see one flickering at 1000 Hz and another at 1001 Hz for example. For battery powered devices, it could easily happen though.
https://en.wikipedia.org/wiki/Beat_(acoustics)
I don't see why the same effect would not happen with the light sources.
That being said, obviously the fact we probably can't see 10KHz flicker, does not imply it has no effect on our well being.
Edit: if you turn your head at the same time, my numbers above are too conservative.
Consider a flickering streetlamp outside your house. Now imagine you have two sets of net curtains covering your window, 10cm apart. The net is very fine - say a 0.1mm mesh.
If you sit next to the window working, and move your head back and forth, you will see a moire effect. If you sit 10cm from the curtains and move your head at 1 m/s, the 'flashing' you see is 50 Khz. If the light source behind the curtains is flickering at 49,995 Hz, you will see the resulting 5Hz flicker when the flicker from the moire effect and the streetlamp get multiplied.
As a regular human, you have now made a 50kHz flicker detectable with no special equipment.
Also, LED's unlike nearly every other electrical device are constant current devices (as opposed to constant voltage, which is what a USB port, battery, or nearly any other power supply offers for example).
Constant current devices must be wired in series rather than parallel, meaning that if you wanted more than one LED per transformer, you would need to break the existing circuit to add an extra LED. That isn't really compatible with standards around electrical plugs - you would need to short out all unused electrical outlets in a constant current system.
Constant Voltage vs Constant Current is another one of those 'DC vs AC' or 'electron has positive or negative charge' issues - We have chosen one standard, and everything is built on it. We could go back and redecide, but all infrastructure would need updating.
The question of supplying LEDs with CC or CV power supply is only the question of efficiency and cost.
Most LED strips are made as a serial/parallel combination of LEDs with an added resistor for each segment, to get the desired current through the LEDs in a segment from a ~12V CV power supply.
You don't really have that much choice when it comes to LED strips. CC power supply would need to generate thousands of volts or you'd need a bunch of them. And that would be costly.
If anything I simplify leds as maintaining a "constant voltage", no matter the current I send through them (in the right direction). Just like other diodes.
> it's easier to regulate the I component of P=I*V for consistency than it is the V portion.
I understand, and we're on the same page. But it doesn't change the fact that almost no led strips do this. You can iron out over individual LED differences by putting 3-4 in the series, and regulate the current using a resistor.
In fact, most of the LED indicators you'll see are driven like this. LED + resistor [+ optionally PWM or multiplexing].
Only for power LEDs you'll usually see anything more complicated invlving DC/DC CC switching power supplies.
I got so far as inspecting factories in Shenzhen, finding a partner supplier, and building some prototypes with my existing manufacturing contacts.
Ultimately, I ran out of time (launched another product instead) - but it always bugged me that I wasn't able to bring this product to market.
If anyone would be interested in picking up where I left off - I'd be interested in partnering.
Shoot an email to public @ proxmark dot com
The software side could be improved.
Also, they've proven to be unreliable—I've had 4 (out of 13) suffer capacitor failure just outside of the warranty period. Their color binning is not good—new lights look totally different in color from the older ones.
I wrote about this and was interviewed on a podcast recently:
* Is Smart Lighting Healthy?: https://medium.com/simplebulb/is-smart-lighting-healthy-903c...
* Podcast: https://bedtimebulb.com/ror
Disclosure: I sell a light bulb meant to be used in the evening before bed. It removes most of the unhealthy blue/green light, has a super high CRI, and has less flicker than "flicker-free" lighting (which could have up to 30% flicker!). Bedtime Bulb: https://bedtimebulb.com/
As another commented mentioned, Philips Hue is a possible alternative/competitor, but unsatisfactory in some respects; precise control over exactly which LEDs light up and the lack of red LEDs in its LED array.
The goal was a fully controllable lightbulb so that blue LEDs could be turned off/reduced in the evening, and red LEDs turned on, gradually. Like you said, Flux for real light.
I do reasonable amounts of manufacturing of other products, so had existing contacts on the ground.
The prototype build was a fully functioning strip with wifi control (and a very basic / terrible app attached).
Sticking points were marketing and bricks and mortar distributions - which are always large problems to solve.
It is not allowed by law (the light has to be either constantly on, or it may be turned off if it isn't dark), it can trigger epilepsy, it is distracting, and it is selfish and not 'cool' at all.
It also appears to be common in PC desktops to enable all kind of LEDs, without allowing them to be disabled. Especially in all kind of colours (which Razor dubbed 'Chroma'). Not my cup of tea, a waste of aesthetic and electricity but the worst thing about it is that I pay premium for such feature because it is deemed 'cool' by the target market.
FWIW, I use a strong light in the morning to wake up. It doesn't flash.
These cheap Chinese LED lights for the bicycle all come with a blink-setting, and like the <blink>-tag of yore, it serves no practical purpose. People tend to think blinking means you are easier to spot in the dark, which is true in the sense that it grabs attention, but as you mention, you can't really extrapolate where someone is going with a blinking light.
The use of the blinking setting is usually born from naivety. People use the setting, because it is included with the light — why else would it be there, if not to use it? Now imagine if every cyclist on a busy cycleway used the blink-setting. At that point this behaviour is downright selfish.
It's not too hard to regulate really. After all, you are already legally limited in what you can use (white/yellow front, red back, no blinking).
> The trick is attracting the attention of people that are not looking in the first place.
This is also known as "distracting drivers" and it's hardly a good thing.
Distracting them from not seeing cyclists?
I wonder what you think of emergency sirens/lights? Too distracting?
If unnecessary, yes.
> Distracting drivers from what, exactly? > Distracting them from not seeing cyclists?
We only have a finite attention span; hence such is going to be distracting the driver from other important things on the road. Not every cyclist is so important to be noticed.
You should also take into account that a blinking light means the driver is changing lane or course. Two blinking light means danger. If every bicyclist would all the time be signalling "danger, danger", people become desensitised to such signal.
Excuse me for keeping my flashing lights on the bike when there's people with attitudes like yours controlling several ton killing machines within meters of me.
Maybe I'll order some brighter lights...
In the NL, yes I might call it selfish. In NYC, not so much.
http://www.gp.se/nyheter/g%C3%B6teborg/inga-blinkande-framlj...
The christmas tree effect probably doesn't keep cyclists safe, although it's tricky to research this.
I'm really confused by this thinking. If there is a blinking white light pointed at you it means the cyclist is on the other side of the road, traveling with traffic in the opposite direction. If it is blinking red then you are approaching the cyclist traveling in the same direction as you, on your side of the road. If you see both lights blinking, with the white light on the left, then the bike is traveling left across your direction of travel. White on the right for the opposite. What information am I missing here? I feel like any of these combinations should be enough for a driver to notice a cyclist and to give them a sufficiently wide berth.
Do drivers know this? Or do they think the flashing light is something else? Do they even see the flashing light? It's possible that eye movement across a scene means the eye travels over the cyclist in the off-time of the light.
As a driver I've two things to say about them.
Firstly, they do make it easier to spot the cyclist over a solid light so that's a good thing. However, it's almost impossible to track their movement and that is a very very bad thing.
The best solution I feel is to have a flashing light which draws attention in addition to a solid light which is much easier to keep track of in your peripheral.
Now its fine to only use flashing lights - Rule 60 of the highway code:
"At night your cycle MUST have white front and red rear lights lit. It MUST also be fitted with a red rear reflector (and amber pedal reflectors, if manufactured after 1/10/85). White front reflectors and spoke reflectors will also help you to be seen. Flashing lights are permitted but it is recommended that cyclists who are riding in areas without street lighting use a steady front lamp."
https://hackaday.com/2018/10/17/diy-arc-light-makes-an-unnec...
And as they are illegal to use they should probably be illegal to buy, at least when marketed as bike lamps.
But cyclists tend to get a pass with almost everything for some reason.
I use a 1200 lumen bike light, powered by two 3500mah 18650s.
If I were in a trolley problem and would have to decide between my own life or my daughter's I would die to save her life.
Likewise, if this society does things which endanger my daughter's life I'd like such threats eliminated.
I'm convinced this is one of the destructive examples, especially if it becomes popular or the norm.
https://www.lrc.rpi.edu/resources/pdf/iesna01a.pdf
> Flashing lights will be perceived as having higher brightness than steady-burning lights, up to a flash frequency of about 15 flashes per second. Such brightness enhancement can aid in conspicuity, and several rear lighting systems have been designed to have a flash rate between 5 and 9 flashes per second in order to maximize their perceived brightness.
I think deep down we all know this anyway, which is why we want flashing lights if we are on a bike amongst traffic. Why on earth would emergency vehicles and maintenance vehicles use flashing lights if they were equally effective to steady lighting?
Your daughter's bike would be far more noticeable with flashing lights.
Blinking lights in traffic serve to warn us about danger. Bicyclists are just normal cyclists; so the other users of traffic get warning fatigue via your method. A reflector (legally required to be on a bicycle on the back) is going to adequately help them. As a runner, I also wear clothes which contain reflections.
I'm a cyclist and I'll stick with my flashing lights, thanks. I have steady lights as well so drivers can track my motion.
Whatever it takes for those oblivious and distracted SUV idiots to actually notice that I'm there. I've had a few very close calls already, I guess those poor long-suffering drivers must have had warning fatigue. /s
I'm a driver as well and I don't find flashing lights on bikes very distracting while driving. What's much worse are the cyclists with no lights, which makes it difficult to judge their position, or even to notice their existence at all.
If I were going to build a forum today using an open-source platform, I'd probably go with Discourse.
* Discourse - Civilized Discussion || https://www.discourse.org/
Although I do wonder about accessibility. Some of the lighter colours don't pass WCAG recommendations for contrast. But it's rare to find a website outside of gov.uk that even comes close.
But it's terrible for search, both internal and external(Google).
Why ?
Let's start with internal search. Ctrl-f fails in thread search. No other mechanism to search inside a thread.
And about external search:
Permalinks to individual comments - great for the search engine when you request a very specific thing - a specific niche comment from this site could get ranked highly in google.
Also, it's making it easy to link to a great comment is import. Impossible here.
Permalinks to webpages that contain full threads - lots of relevant text for the search engine to chew on. But in flarum the content lazily loads. So maybe Google wouldn't be able to chew on all the comments.
And the fact that when Google finds a thread from the site, he doesn't say how many comments per thread , indicates that he doesn't see this as a forum, which could be bad
And all this is a real shame - it's a community with really valuable content.
Topic list: https://www.talkyard.io/forum/latest
Example long discussion: https://insightful.demo.talkyard.io/-11/my-son-was-sent-home... (of a length that might work less well with sort-by-time + lazy-load approaches)
It's also new forum software (I'm developing it), sort of a combination of Discourse and HN and Slack. I would think it works ok with external search? Becasue, like here at HN, good comments surface to the top, + they're included in the HTMl directly on page load. So, what a search engine sees, ought to be the original post, + the best comments.
I'm wondering, what do you mean with: "Also, it's making it easy to link to a great comment is import"? (What does "import" mean, here)
1. the way you do permlinks to individual posts looks good. It's also easily shareable. good too.
2. but probably, an even better way to do permalinks is something like quora did - just the specific answer that solves the user's problem , in a seperate non-distracting page, with a full, human readable url.
That of course creates a problem with sub-comments, but quora solved it nicely by hiding them .
https://www.quora.com/Google-categorized-me-as-T4-The-offere...
3. Content quality is key for SEO. Assuming that upvotes works well for that. i don't know much about forum design, but i assume upvotes are really sensitive to the community and that's why HN is so great.
but in other communities, i wish there was a way to sense if "this answer solved the issue" or something similar, and letting that rise. That's probably one of the reasons stackoverflow won.
But forums are somewhat different so that's harder.
4. Adding that "recommended links" on the site could help SEO. but it's a shitty user experience. So probably isn't worth it.
Yea, upvotes only work, if the community "collectively" has a good judgement :- ) Also, I'm thinking about weighting upvotes, with how good a judgement the voter seems to have, based on trust levels and fraction upvoted and downvoted answers, hmm. So a staff user's or a trusted core member's upvotes, have a bit more weight, than votes from a new and unknown person.
Being dumped into a forum with no context outside of the URL? thats horrible UX.
Horrible UX. Whats the point of the site? What is LED Strain? where am I supposed to figure that out?
Note that this info is for fairly low power LEDs. When you start having high power LEDs, regulations may require better power electronics, and the cost of the electronics might be amortized against the cost of the thermal cooling solution, etc, so you can make a more expensive electronics package.
1) By stringing ~ 180v of LEDs in series, and adding a current limiting resistor, you can drive the whole thing from the AC line. This has terrible variability (short light spikes every 60hz, and the thermal effects will change the LED properties so much that you could easily have 2x light intensity change as they warm up) and poor total illumination (as most of the cycle is spent with the AC waveform lower than the needed voltage. I haven't seen this in the wild, as option 2 isn't much more expensive and far better.
2) Use a single diode + capacitor rectifier to generate ~180v, and then have a similar string as in (1). This gives far better illumination (the capacitor will probably stay in the 160-180v range), but still has substantial 50/60hz ripple based on the size of the capacitor
3) Similar to (2) but use a full bridge rectifier instead of a single diode. As we are now driven by a rectified sine wave, the ripple voltage will ~half, and the ripple frequency will now be 100/120hz.
4) Many applications don't have ~60 LEDs in series, so you can't drive directly from the rectified AC line. The first stage is a rectifier, and a second stage most likely is a buck converter. The quality of the light out of this depends on how much you care about power factor. Chips like NCL30288, for example, maintain high power factor and fairly low lighting ripple. Most people won't notice this.
5) Particularly in higher power lighting, a separate power factor correcting stage achieves high power factor, and a second stage generates a constant current that should have exceptionally low luminous intensity ripple (if designed right). The ripple frequency should be in the hundreds of kHz as well, so I don't think any eye could notice this.
And don't get started on dimming, I haven't found a product on the market that does non-phase cut dimming in <20W lights.
I'm fairly sure the IKEA bulbs use the above method. If you turn them off they have an afterglow for a couple seconds.
I could be entirely wrong though, someone should probably dismantle one and figure it out.
I'm curious if folks in countries with 50Hz mains have the same issue. At that point it might be so bad that products without at least a full bridge rectifier would be unsellable.
Also, most of the "Edison-style" LED bulbs on the market use really cheap drivers. This is especially true outside the U.S. where you can get an LED "filament" with integrated half-wave rectifier. Thankfully UL is not allowing this crap in the U.S., but Edison-style LEDs here still (mostly) use very cheap driver topology.
I'm on a mission to make lighting healthy. That's why I launched Bedtime Bulb: https://bedtimebulb.com/ We have the lowest flicker of any bulb I have ever seen, even less than those claiming to be "flicker-free."
Similarly for LED lightning in the garage.
For the kitchen I had a need for rope lighting and never did find LED/driver combo that I was happy with.
The built-in LED spotlights that came with my house flicker like a rave concert whenever I capture a video in slo-mo. It's unsettling.
Phillips LEDs, especially the Scene Switch bulbs, are flicker-free according to my tests. Surprisingly, older CFL bulbs flicker much less than LEDs.
This is mostly so that the display can be battery powered, because the availability of AC power on shelf is pretty hit or miss. I wouldn’t trust a display to indicate if the bulb has flicker or not.
I can't imagine those are battery powered or that every different bulb on display has been modified.
I was surprised to see flicker even on my $10 a bulb Soraa lights which are top of the line, cri 92+ bulbs.
Psychologically. Jimmy clearly demonstrated that his symptoms were all in his head.
Clicking your teeth together makes it pretty apparent usually, the segments will appear to jump around. Try it at home!
2) They often don't? A lot of LEDs flicker at something like 60Hz. Sure: if you stare at the light you might not notice it blinking, due to the limitations of the sensors in your eyes that can weirdly "get tired" of looking at the same thing for too long, but if you move your eyes across the light quickly you will see it blinking as now you are getting a broken dotted line carved into your vision. I find this maddening when there are such lights in my peripheral vision.
If you're shifting your view/moving your head you can easily perceive the flashes.
Perhaps some brains perceive/process the small, quick changes that most of filter out.
Find a LED light that isn't on a continuous DC power supply. Christmas lights work well for this.
Pick two objects, one far to the left of the light, one far to the right. Focus on one side, while making sure the other object and the light remain in your field of view. Next, glance at the second object so your eyes quickly travel across the LED.
If you have christmas lights you can exaggerate the effect by spinning the cable. You don't need to move your eyes at all in that case.
That said, I can eliminate all annoying flicker by making sure that all of the things that flicker aren't mixing down into ranges that start to annoy me. For example if you have some LEDs that are running at 15Khz and some that are running at 15.1Khz they can set up a beat frequency at 100Hz that is annoying. I had some dimmable can lights that did this and figured out that the PWM was local oscillator based (R/C if you can believe it) rather than crystal based. I found lights that used the line frequency to drive their oscillator so they are essentially all in sync (at 2.4KHz or so, so not noticeable to my eyes)
That applies to (about) everybody, for large enough stimuli. Rods are more sensitive to flicker than cones and you don’t have that many rods in your fovea. See https://en.wikipedia.org/wiki/Flicker_fusion_threshold.
Many people can see it, but don't really notice it... until you point it out. I pointed it out to one guy that owned his TV for a year and never noticed it, but after I pointed it out to him, he couldn't stop seeing it and could never enjoy his TV after that.
Wobbulation
Bought a 2018 Macbook pro and it produces similar symptoms like years ago when I had a laptop with bad low freq LED backlight.
Right now using a late 2010 and a 2013 Macbook Pro both with native screens and on external screens and it does not make my head hurt. 2018 one strains me both on native screen and on my otherwise good daily driver BenQ monitor.
Edit: I know W-OLED used by LG does not have PWM problem, but that is not for mobile uses.
https://www.reddit.com/r/apple/comments/7uv6m3/iphone_x_uses...
In summary they are saying that low frequency (240Hz) PWM is used for amoled because it decreases sub-pixel wear, it prevents color distortion, it's cheaper. So it looks like this won't change. I got an amoled phone and was surprised that the experience was worse than LCD (for me - it seems to depend a lot on the individual). Didn't even know that PWM was used until I started googling eystrain and amoled. Anyway, I sent the phone back.
(edit spelling)
Sure, when the AC is on in late spring/summer, LED makes a heck of a lot more sense. But when the heat is on, filament lightbulbs serve as space heaters as well as glowy-warm lights.
And with the whole open question of blue light and retinopathy, tells me that until this is resolved that again, incandescents are better than LEDs. I already knew that those damned 'blue LEDs' are painful at night. I now know why.
Its only during the warmer parts of the year do they turn into a significant burden, energy wise.
Update: the title has since been changed to 'LED Strain'.