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Ask Slashdot: Does LED Backlight PWM Drive You Crazy?
jones_supa writes "I would like to raise some discussion about a hardware issue that has increasingly started to bug me: backlight flicker, from which many LED-backlit monitors suffer. As you might know, the backlight and its dimming is driven by a pulse width modulated square wave, essentially flicking the LEDs on and off rapidly. Back in the CRT days a 100Hz picture was deluxe, due to the long afterglow of the display phosphor. LEDs, however, shut off immediately and my watering eyes and headache tell that we should be using frequencies in multiple kHz there. Unfortunately we too often fall behind that. As one spark of hope, the display review site PRAD has already started to include backlight signal captures to help assessing the problem. However with laptops and various mobile gadgets, finding this kind of information is practically impossible. This issue sort of lingers in the background but likely impacts the well-being of many, and certainly deserves more attention."
So do LEDs bother your eyes? I think CRTs gave me headaches far more often than has any form of flat panel display, at least partly because of the whining noise that CRTs emit.
Your comment gave me a headache. Also, are you allergic to Wi-FI?
Might be a first world problem but that doesn't make any less real.
It will never change unless someone starts the conversation.
It's just you.
If you're sensitive to them, don't buy them.
Please don't make every LED / LCD on the planet more expensive because of a tiny minority of people who blame things like PWM for their symptoms (correctly or not).
Like with flourescent lamps, and people who can't be in an air-conditioned room, and people who have to play games with altered FOV's because it makes them sick. You're a tiny minority, or else half the world would feel ill all the time. Please find another way to cope with it (i.e. glasses, double-blind tests to convince yourself it's placebo, or whatever).
Some high-end displays flicker like a movie projector, only turning on LEDs during the refresh interval when the entire image is cached by the TFT so there's no tearing at all, not even as much as a CRT. If this is true you might find those expensive displays especially annoying.
If it's PWM annoying you, shouldn't setting the display to max brightness entirely fix the problem? I wonder if you're picking a scapegoat for your headaches.
I think you literally do not understand what the word "literally" means.
So do LEDs bother your eyes? I think CRTs gave me headaches far more often than has any form of flat panel display, at least partly because of the whining noise that CRTs emit.
No. You're imagining things.
But, that being said, you're not alone. I heard somebody walk into the retail establishment that I work at and said, "I'm disappointed that you guys installed automatic doors that emit so much radiation, but I'm glad that at least you don't have horrible fluorescent lights that would make me unable to shop here." Of course, she was saying that standing under about 500 CFL's that she assumed weren't fluorescent because of their size, shape, and color.
I don't respond to AC's.
One thing I do know was/is a problem with monitors and eyestrain has to do with fluorescent lighting in the room. We can't see it with the naked eye, but the fluorescents are also flickering at 60hz and I've had it happen in the past that if the CRTs I was using were out of sync, (running at 75hz or similar) after a while I'd get weird eye strain from something we can't consciously perceive but our eyes still try to correct for. I usually solved the problem by either setting the CRT sync rate as high as it would go or syncing it to 60hz, or preferably getting rid of the fluorescent lighting completely in my workspace when possible. Maybe a similar effect is at work here?
No. Used plenty of LED displays without issues.
-- Using the preview button since 2005
I cannot wait until I get old enough that I cannot hear the whine of CRT. I don't care what that means for my hearing, that noise alone is just... gross feeling in my head.
I think you literally do not understand that some words are used in a figurative sense.
No. You're imagining things.
Happened to me once that I got upgraded to a larger monitor, and when I turned it on it was like being physically smacked in the face. It's a long time ago so I can't remember exactly what happened then, but I didn't use that monitor.
I stare at various LCDs for 16+ hours a day without any problem. I'd even go so far as to say I have sensitive eyes. I can't attest to newer LEDs. I've installed a few for video conference units, but I don't spend my day looking at them. They're definitely not any worse than a CRT. I used to have two giant CRTs on my desk and they'd damn near give you a tan.
When we first got LCDs in high school (circa 2004), I still had all CRTs at home. I found the LCDs hard to focus on for more than fifteen minutes at a time. However, once I switched to using LCDs everywhere (home, school and work), the problem went away. Now the only time LCDs give me an issue is if the backlight is just too dim and even that I get used to if I use the monitor long enough.
I find it to be much more of a problem using someone else's keyboard because the key spacing is never the same.
also, is this an advert for prad?
I hope not, dass vor Ort saugt wie ein östlich Deutsch im Urlaub.
I still hear people complaining about fluorescent lighting despite the fact that CLF's have electronic ballasts that use extremely high frequencies. I could understand the old, old lights that used magnetic ballasts, but CLF's? Really? Seriously? People can see 40,000Hz on a properly working tube bulb? It is not like a monitor with tiny phosphors where I could see the scanning. LED's flicker way more than I ever noticed fluorescent lights. To make matters worse, LEDs are used in many more places! I noticed the flickering from the taillights in newer cars, gadgets, LED equivalent bulbs that dim, etc.
Never had any issues with LED displays of any kind. My TVs and PC screens have been LED for years now. I don't have a problem with the question, but I think this is getting into an issue where the person asking the question is in the minority and would like believe that almost everybody else is in the same boat so maybe they get something going to "fix" the problem. For example, based on personal observation, I'd say that about 10% of the population has some kind of vision issue where they cannot see 3D videos at all. Trying to watch those gives them headaches or makes them ill. Those people always complain the loudest about how 3D "sucks" and insist that it's going to fail because they think that everybody on earth has the exact same problem. I'm willing to admit that the original poster may have a very real problem, but is it common enough to attract attention from the manufacturers? Probably not.
I thought I was the only one - but perhaps I still am - but car LED brakelights have been driving me ***CRAZY** for years!!!!
If you wanted to use the phrase "literally" to mean "figuratively", couldn't you have just said "figuratively"?
http://en.wikipedia.org/wiki/Saccades
The average (quality) CRT is perfectly fine for most people. They do not emit any high-frequency noises, nor do they have major flickering or geometry issues. To suggest that all CRTs are crappy is doing them a total disservice.
:)
That said, there are plenty of CCFL-using LCDs which have given me dry eyes and a funky feeling after staring at them for a while, possibly due to the polarized light. Or perhaps just because they were low-quality pieces of junk.
If you want to check if there's any significant flickering that'd annoy you, check the display from the corner of your eyes. The peripheral vision of the eye is far more sensitive to motion than the central part you generally focus on. If you can't see flickering with your peripheral vision, it's just not there for you.
Thanks for the whine story, though. Would you care for some cheese with that?
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Like you I get headaches from looking at CRT screens. I could never stand refresh rates below 80 Hz. The problem is I need a lot of screen real estate and usually the lower end monitors can only do higher resolution at lower refresh rates. Interlace mode is even worse.
So when LED came out I rejoiced. It is a God send for me. I never needed glasses until I was diagnosed with astigmatism. I work exclusively with computers and blame CRT monitors until now.
So while I am bothered by the flicker on LED monitors, I am also thankful for it being a huge improvement over its predecessor.
Take off every 'sig'!
All your 'sig' are belong to us!
Back when I was using CRTs I had to have 80Hz minimum, and 85Hz was the point at which my eyes no longer felt "weird" for lack of a better word. I currently have a Dell S2230MX for my main screen and it's LED backlit and I have no issues at all. For what it's worth, unrectified LED Christmas light strings drive me bonkers with their strobing, so not really sure what to say on this one.
Neither I, nor anyone I know has ever complained about this. However, it's not the first time I've heard about this complaint. And my mind is starting to play tricks on me: I just "noticed" some flicker on an LCD monitor (fluorescent backlight) I've had for years.
I can't conclude whether or not the issue has any merit, but my preliminary conclusion is that discussing the issue tends to cause it.
So do LEDs bother your eyes?
You need to do double-blind testing to see whether you are really bothered by the LED flicker, or you just think you are bothered by the flicker.
...has increasingly started to bug me: backlight flicker...
Perhaps it has increasingly started to bug you because you are becoming increasingly aware of it, and not vice versa.
.
It is a common marketing ploy to create a perceived problem, then magically have a product available for sale that just happens to assuage that newly perceived problem.
I think you literally do not understand what the word "literally" means.
The difference between an xray tube and CRT tube is disturbingly subtle.
So do LEDs bother your eyes?
No. Can't say I've ever seen or heard of anyone having trouble with LEDs specifically. I honestly cannot even see a flicker in most LED screens whereas I was pretty sensitive to it on CRT screens. I find LEDs to be much easier on my eyes than even the best CRTs. I've seen light sensitivities that are due to interactions with poor quality or old fluorescent bulbs. My last office was next to a window which made for some glare problems and excessive brightness problems at times. I've also seen issues with brightness due to external stimuli or just a larger brightly lit screen. My wife is actually rather light sensitive so I had to dial the brightness down on a 24" monitor at home.
I'd be curious it the original poster's issue is with the LEDs or with the backlighting or with something else unrelated to the LED screen.
White LEDs actually do have a nonzero rise and fall time(because if it says 'white' on the label, that means 'glob of phosphor being pumped by a blue or UV die, since we don't have wideband LEDs'). Also, a quick look through the datasheets shows advertised PWM frequencies in the 200KHz-1MHz+ range. Are the cheap seats substantially slower?
square wave energy clogs radio bandwidth. plasma TV is just awful at putting background noise out there, and the undercabinet light power packs are also pure evil.
if this is supposed to be a new economy, how come they still want my old fashioned money?
I usually couldn't see any flicker at 60Hz and never above 72Hz. Most of the ones with apparent flicker were older monitors that usually had a perpetual burnt capacitor smell lingering around them.
He probably also has to walk 15 feet to grab a new Cheetos bag.
It's 15 feet to the soda machine. Cheetos are 17 feet away you insensitive clod.
Will OLED's have the potential to flicker like this?
I notice a 'walking pixel' effect on my laptop once, so this could the effect in action.
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I have absurdly fast eyes. I cannot stand any CRT below 80Hz. I can see red, green, and blue in separately in any DLP projector with any color wheel frequency. LEDs in taillights in modern cars like Lexuses drive me insane because it looks like a trail of blinking LEDs to me. Even LED glowsticks bug me and people don't believe me until I wave them back and forth to prove they're flickering. And yet I've used a dozen different LED monitors, maybe even hundreds, and never had a single problem with them. The diffusion of the screen blocks the blatant flicker that's likely occurring. I think the author of this article merely has too much caffeine or is eating crunchy granola while using his monitor or something because if anyone would have a problem, it would be me, and I don't.
Waa my computer is too flickery, someone call the waambulance.
For people with photosensitive epilepsy, it might more more like "someone call the ambulance."
We have a user here who got a new laptop last summer, it had a LED backlit LCD. Within 20 minutes she was calling saying it was making her feel sick/headache. We tried adjusting refresh rate, brightness, no help. Put a CFL backlit LED laptop in front of her and she was fine. Tried LED standalone monitor, it also bugged her though not as much. So, we had to find a laptop that had a CFL backlit screen, wasn't junk,and met our other requirements (docking connector mostly). Ended up getting a previous year model Toshiba Tecra with a Core2Duo.All the rest of the laptops we bought had i5's in them by that point.
You do realize that right? The refresh rate is how often new data is sent to the pixels on the screen. The backlight is the led's that surround the edges of the screen. They are unrelated.
Most PWM controllers use a few 10's of khz upto a a few using low 100's of khz. If you look up the ramp up current of led's you'll see they arent instant on/off either, so your point is really moot on two cases.
UDL
The difference between an xray tube and CRT tube is disturbingly subtle.
Fortunately most of the EM radiation from a CRT monitor goes out the back, not through the screen. You're frying the guy sitting in front of you, and you need to worry about the monitor behind you. However, it is most not all. You still get a dose from your own monitor too.
Some mornings it's hardly worth chewing through the restraints to get out of bed.
Hey, jones_supa: It's not yer monitor, stoopid, it's yer cellphone... stop holding it next to yer head!
Waa I heard someone make a complaint that doesn't affect most people in third world countries, someone call the waambulance.
Add a 10pF cap, no more flicker. But seriously, i have had ZERO experience with this. None of the 20+ laptop/desktop screens we have at work, or my screens at home (TV/computer) flicker at all. They are all cheap crap LEDLCD's. A few are the newer LEDIPS. Zero flicker. Even when filmed with 60hz cameras, no flicker at all.
No, he's not. That whining noise is well known, objectively measurable, and explainable by actual physics.
Unless IBM was imagining things.. Or you deny the existence of eddy currents in what is essentially a high frequency electromagnet (see material under "stray losses").
But, that being said, once you've blown out your hearing above 15 kHz you have no reason to believe that high frequency sounds exist -- dog whistles, ultrasound machines, animal ecolocation are all a giant conspiracy to fool you, not features of the real world.
Idiot. You are very likely in the majority that cannot see that flicker. There is a minority that can, and for them it is a very serious problem.
Using higher PWM frequencies is not an issue at all, it just has to be done.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
That's like saying herbicides and insecticides are almost the same because they both contain water.
The differences between a CRT and an x-ray tube are not at all subtle. OK, they both have filaments to boil off electrons and both use a high voltage to accelerate them, but so do certain types of amplifier tubes and some types of particle accelerators.
If you do a quick web search you can easily find out just how different they are.
You are just another asshole saying hurtful things without even understanding the problem. There is a minority in the population that can see lower-frequency flicker. You are very likely not one of them, or you would not say such incredible stupid things.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
For over thirty years now I've been working with various display devices of a wide variety of design, manufacture, size and refresh rates. About sixteen years ago I started having the symptoms you describe -- headaches, watering eyes, etc. The internet back then isn't what it is now, so my first reaction was NOT to post something on a tech forum and open myself up to a lot of ridicule and abuse. Instead, I made an appointment with an ophthalmologist. After a thorough examination and some tests he advised me to take occasional breaks from the monitor throughout the day and rest my eyes. He also gave me some techniques to use for this. I took his advice and my symptoms went away virtually overnight. I have not had any problems since.
You should go see an ophthalmologist -- not an optometrist -- but a real eye expert. You might be surprised to learn that your problem has nothing to do with refresh rates or anything of the sort.
Proverbs 21:19
There was a documentary on that in the early 90's http://en.wikipedia.org/wiki/Joe_Versus_the_Volcano starring Tom Hanks and Meg Ryan.
Jesus was a compassionate social conservative who called individuals to sin no more.
Idiot. Try finding out whether something is valid or not before posting nonsense. Here is a hint: A small part of the population can see flicker in lower frequency ranges, while most cannot.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
Well, solves your problem, anyway. Solution to high-pitched sound for dodgy electronics: ride your motorcycle to the gun range.
There's a huge difference in the amount of power a standard WAP emits versus how much you'd need to span 1.5 km at 5 GHz.
Hail Eris, full of mischief...
E pluribus sanguinem
The screen refresh rate of the LCD pixels is not the same as the LED backlight refresh rate. The LCD refresh rate is more analagous to the refresh rate of an analogue monitor, and like phosphors, it does take some picoseconds for an LCD cell to fade once it's power is ceased, so you get the "smoothing" of the images in the same fashion.
The LED refresh rate, on the other hand, has to do entirely with the light behind the LCDs. Whether those shut off immediately or not I don't know, but I've certainly never had a problem and I'm very sensitive to refresh rates (they trigger migraines when too low.)
Switching to an older style monitor that doesn't use LED backlighting would resolve the problem for the original poster. Cranking up the refresh rates on the LEDs would induce more flickering, not less, because they don't have a decay/shutdown period according to them.
I do not fail; I succeed at finding out what does not work.
More and more autos, trucks, and buses are using LED's for taillights/brakelights, and the PWM frequency they use is slow enough that I can notice the strobelight-like effect when the vehicle is moving or I move my eyes. It's very distracting, and I really don't see the reason why they can't raise the frequency enough so it isn't noticable anymore.
Are YOU using the TOOL, or is the TOOL using YOU? Think about it!
You're blind, those knobs were called "breasts", and that smack in the face was an offended woman slapping you in the face for "turning on" her "knobs". Her lovely lady knobs...
I suspect author is also bothered by wifi signals emanating from his router.
If my eyes are watering after a long session its because my screen is too bright, which is exactly the opposite of what he postulates as the problem (on off cycles of LEDs). Brighter requires longer "on" cycles, which in turn are less perceptible. Yet for most people overly bright screens are the source of complaints.
Sig Battery depleted. Reverting to safe mode.
Because it wouldn't take long before people would start using "actually" the same way they currently use "literally." People will always misuse words they either don't understand or misheard someone else use. It actually burns me up when I hear it, but there's no changing it.
And when I was eight, I picked up a book from the 1970's that suggests putting strobing LED's on your bike using a PWM circuit. They've been around forever. Hell, I have an LED alarm clock from when I was that old that runs off the mains voltage.
Very, very, very few people are sensitive to these things. In fact, most of the these things are present more in your everyday life than you even imagine. Like the warnings for people with photosensitive epilepsy, these people won't be able to use commodity electronics if their symptoms are actually that consistent, and the number of people like that are vanishingly small.
But if you ask people, you'll find that 1 in 3 think they are sensitive to something-or-other that actually can't be verified at all, like the examples I state. They've heard they are bad, or they think it's bad, and lump themselves into the same category as people who can "feel" microwaves coming out of their wifi or whatever other nonsense.
I'm not saying that this guy's monitor doesn't make him think he's ill. I'm not even saying it doesn't. I'm saying the chances are it has more to do with a noise from the PSU, or a particular smell, or even the heating of the air above it. And if it does - well, what do you want us to do? Throw all the LED's in the world in the bin? No. You'll just have to learn to cope with it.
I'm sorry about that, I really am, it must be a pain. But there are people who can't play sports, people who can't not wear glasses, people who can't be outside in the summer, people who can't breathe if you spray air freshener, etc. The only thing you can do is not do those things, or find a way to manage your symptoms.
I think you literally do not understand that some words are used incorrectly even in a figurative sense.
Am I the only one who has an issue with this definition? I realize that English is an evolving language, but it seems like this became a new definition because too many people were too fucking stupid to understand the actual meaning of the word. Similar to how the word "epic" no longer has the same impact it once did. Perhaps we can redefine "figuratively" to have the classic meaning of "literally".
Another cause of "walking pixel" is the dithering needed to get smooth gray ramps on a 6-bit TN LCD. Most panels will perform "temporal dithering", changing the dither pattern from frame to frame to make it less visible for still images.
If you hate 1st world problems so much, *PLEASE* , feel free to go live in the 3rd world. I'm sure you'll be much happier hearing your neighbors complain of 3rd world problems.
You probably couldn't hear me whining about my partial blindness...
They both generate X-rays...
PWM brake lights and tail lights are bad for me though.
Bright enough to leave a brief afterimage so when you move your eyes there is a blinking tracer.
umm? what does the pwm have to do with afterimage? that's some magic time warping blinkin you got there.
world was created 5 seconds before this post as it is.
It's possible he's imagining it. But can you entertain the possibility that he isn't? I can hear fluorescent lights (including CFL's, though many of them make a quieter and higher pitched sound at the top of the range of what I can pick up) and they drive me insane. Same thing with CRT's and cheap LCD's. If you've ever heard a fluorescent light as it nears the end of its life, as I've found many others can, it's a similar experience only sharper.
Naturally, my wife suspected hearing this stuff was all in my head (why wouldn't she?) so we did tests to prove it. The most dramatic example of this is with a CFL dimmer bulb Philips used to make (not sure they do anymore, seem to have switched to LED). They're probably the loudest and most annoying lights I can hear, but the difference is one of degree and not kind. Even in another room of the house, I can tell not only whether the light is on but even the setting it's on by the pitch it makes.
I run my monitors a bit brighter to cut that problem. The only time I've noticed flicker is running at minimal brightness.
Am I the only one who has an issue with this definition?
Yes, you are literally the only one.
My laptops are at full bright usually, my desktop lcds are usually around 80%. My rooms typically have >10klux of light. I like bright. But as i said before, never had a problem with flicker on a working monitor.
Seriously, LED-backit monitors a big improvement on the cold cathode monitors, where the cold cathode would fail after a while, or backlit unevenly when first switched on, until fully heated up.
The old CRTs had low refresh rates, and even the nice Trinitron ones had those annoying mask wires crossing the face of the monitor.
I think the OP is whingeing, and should get this tin foil hate professionally fitted next time.
Oh, I should add that I've never been able to hear anything from LED's. I wouldn't assume, therefore, that no one can hear anything from them.
I can actually see the flicker effect he talks about - on some rare models. I can only see it near the edge of my vision (where your eyes are primarily motion/change sensitive). 70hz seems to be about the point where this stops, but anything lower than that is perceivable to me.
Just like I can hear that irritating whine he talks about (though likewise, not all of them do that)
The inverter on my LCD at home actually makes all sorts of horrible whines if it's in standby mode - so I either leave it on or unplug the thing.
For large sets, this will be our guide even unto death, for the LORD will work for each type of data it is applied to...
When I slam 3-4 red bulls and have a Pot of 2X strength coffee being consumed fora marathon session. But at that point I can see the overhead lights flickering at me.
Do not look at laser with remaining good eye.
I can see the flickering of fluorescent lights when I look beside them, so that they are at the edge of the viewing field of the eye. I think many people could do that if they learned how to.
It is 2 times the power frequency normally, 100Hzz here in Europe, must be 120Hz in USA then. If something is wrong with the lamp it can be 50Hz / 60 Hz.
No. Why was this survey question posted as a story? Surveys are supposed to be in a slashbox, not the main section of the page.
No. You're imagining things.
I used to imagine that whining so well that when we closed down the computer lab in school, I'd known when someone left a monitor on when they turned their computer off, and walk right to the monitor that was still on and turn it off, too, just by following the imagined sound. Since being able to hear 15khz is apparently an imagined ability, I was apparently using my psychic powers instead to find the monitor that was still on. Now doubt this is a much more believable explanation.
"Convictions are more dangerous enemies of truth than lies."
Old CRT were giving me pretty severe headackes. This has all disapeared as soon as I used TFT panels, even with the early models that were not as good as recent ones. I definitely could see flicker on CRTs, I cannot anymore on TFTs.
Maybe you need to turn off "true motion" option on your TFT TV ?
Damnit! Now I can't not see it. I was fine untl you pointed it out. Thanks for ruining my life forever.
I remember an old DOS app called Flicker Free, where the screen would scroll smoother and you could change colors... maybe it needs an update!
What do you think of the people who claim to be sensitive to wifi? They could give the same line you are.
Not taking sides on whether the GP is being hurtful, or the submitter really is in that much pain, but I feel there is a certain point where scientifically we should be able to say "no, you're just being a hypochondriac".
I've had similar problems as I have gotten older, but I don't think that it is the light frequency (for me). Instead, I think that I just can't punish my body like I used to do.
I'd try the following things before getting too worried:
1. Take work breaks every 30 minutes;
2. Update my eyeglass prescription;
3. Make sure that no other bright light sources (like windows) are in your field of view when looking at your monitor (It should be the brightest thing in the room);
4. Sleep 8 hours a night;
5. Don't use the computer when you are hung over;
6. Take allergy medication if you have seasonal allergies.
When I do all of the above, I don't get headaches or watering eyes. Generally, I do not do all of the above, but happily accept the headache or watery eyes because I know that I can make it go away if I sleep more.
I will agree with the Cadillac taillight issue. It doesn't give me a headache, but it does have a Persistence of Vision effect which disorients me. As the vehicle moves either subtly in it's lane, or changes lanes, it leaves a trail of ghost images which occupy a significant part of my field of vision. It's a good thing these are (for now) in the minority. I don't understand how these could have been approved from a safety perspective.
I thought my new monitor was awesome and bright until I opened Excel. I could barely look at the screen!
Sure, in both devices, X-rays are produced at the surface of the anode. However, since the anode voltage of a CRT is much lower than that of a purpose-built x-ray tube, the energy level of these x-ray photons is very low (the wavelength is long) such that the glass of the CRT itself blocks most of the radiation. Any metal shielding around the tube blocks even more. X-rays produced by the impact of electrons with only 10-25 kev energy just don't penetrate well.
I suspect author is also bothered by wifi signals emanating from his router.
If my eyes are watering after a long session its because my screen is too bright, which is exactly the opposite of what he postulates as the problem (on off cycles of LEDs). Brighter requires longer "on" cycles, which in turn are less perceptible. Yet for most people overly bright screens are the source of complaints.
Ah, the good old "it doesn't happen to me, he's a liar" reasoning.
PWM lighting is annoying if the frequency isn't high enough. Rates that that drive me crazy don't drive everyone else crazy. I perviously didn't know why some displays made me slightly nauseous and others didn't until I started to dabble in electronics and learned what PWM actually is and built a circuit that gave me headaches.
I don't understand how the carrier frequency is chosen in consumer goods, but it seems in times past it was based around whatever clock source was conveniently available, and those sources are generally completely arbitrary. I found is rather funny how one arbitrary number can make me hate your product if it wasn't high enough.
To be fair, things are a lot better for me now than they used to be. Probably because the conveniently available clock sources are faster now, or maybe some switched to adjusting the current directly? Maybe also that VFDs and LED displays have given way to LCD displays. And nothing was worse to me than a CRT with phosphors that decayed faster than the retrace. Yetch.
More Twoson than Cupertino
Just because you've never had a problem doesn't make it non existent. No one is going to take away your new shiny monitor.
Most companies run infrastructure to failure. That means fluorescent lights with magnetic ballast that flicker at 60 Hz x 2. Previously, an old CRT with worn out phosphors running at a close frequency would have very noticeable flicker. The beat frequency (difference or lack of sync between two rapidly flickering sources) is what matters. Personally I could see some flicker with a monitor under fluorescent lights up to 70 Hz. Some coworkers always left their CRTs at 60 (where flickering was most noticeable) and we're never bothered. LCDs with CFL backlights generally don't have Mich of an issue (high frequency driver due to size).
I can see how an LED backlight with faulty circuitry could become an issue, especially if it has a flicker close to powerlines frequency. Again it would not be noticeable to everyone. That doesn't make it psychosomatic. Just means the guy who sees it has a slightly different visual cortex in hos brain from you (faster clock speed)? Stop throwing around this nonsense and accusing the OP of being allergic to WiFi too.
By the way, if you ever work in a large company or government, you often will be stuck with degrading equipment for quite some time. Especially outside of IT.... I feel sorry for the OP if this is the case as if his boss can't see it, he's stuck with it until it breaks or he quits.
Also someone mentioned LED lights on cats. Cars run off of DC, but voltage regulators and alternator can add a pulsation to any lighting.
When I got my first LCD back around 2004 or so I noticed a very strange effect. Text, mostly green and red on a black background, would stand up off the screen. It was liking I was reading the text in 3d. At first I thought it was kind of neat, then annoying. Over the years it has went away for the most part. Every now and then I notice it.
When I first saw this I though it was something like the 3d effect that 3d movies use. But then again I and my daughter are among the 10% that can't see 3d movies. We goto a 3d movie and they look just like regular 2d movies to us.
Supporting World Peace Through Nuclear Pacification
I wouldn't worry too much about missing 3D movies. Whenever I've gone to one, it's been a really cool 10 second 3D logo animation before the movie starts and then the rest of the movie just looks like a waste of money. (Which isn't really all that different from how most 2D movies look these days).
Once in a while, after a long day of staring at my monitors, sometimes my eyes will go out of focus slightly and it will appear slightly 3D depending what's on the screen.
This goes for LED brake lights, LED Christmas lights, and LED traffic light, and roadside LED signage.
I find the PWM flicker of LED brake lights _VERY_ disorienting.
Monitors I can aviod.
The glass in modern (well, sorta modern) CRTs is leaded specifically to screen out the X-rays. Yes, they are softer than you'd get from a purpose built tube. You can jack that up somewhat by upping the supply voltage to the tube if you want an X-ray generator. Older CRTs were easily re-purposed as X-ray tubes suitable for home experimentation. You could even find instructions for it in science books for older kids and teens.
If my eyes are watering after a long session its because my screen is too bright, which is exactly the opposite of what he postulates as the problem (on off cycles of LEDs). Brighter requires longer "on" cycles, which in turn are less perceptible. Yet for most people overly bright screens are the source of complaints.
You could put a 'privacy filter' on the screen that will reduce the brightness (with an intended side effect of reducing viewing angle)
And insecticide and iced tea both contain water, yet they aren't really very similar, are they?
You're overlooking the biggest difference between the CRT and the x-ray tube. One is designed to produce short wavelength radiation, in abundant quantities, and the other is designed to produce meaningful, controllable patterns of light and just happens to produce a very minor amount of X-ray radiation. I'll leave it to you to figure out which is which. No, they aren't similar at all.
Every problem that a slashdot reader has is a first world problem. Unless you're dying from or transmitting a disease, starving to death, cannot find clean water, have too many children because you don't about contraception, or are growing up uneducated, your problems are most likely all first world problems.
- Vincit qui patitur.
In all seriousness, I think it is just that the OP has a poorly-constructed monitor. I have used an LED backlit laptop for over a year now (an Asus EEE, so it's a pretty chap computer) and it has not bothered me in the least. I saw a comment that suggested wiring in a capacitor, but I wonder if there is a missing or ineffective capacitor in there somewhere that is supposed to mitigate this, and that it was either omitted to save $.02 on the manufacturing costs or if it was from a bad batch.
As for the rest of you, you're acting like a bunch of assholes. Fuck you all. If you aren't in his seat, you don't know if the problem is real or not.
www.wavefront-av.com
Here is your brightness control. Brightness
Go check out the HardOCP display forums. There are lots of people sensitive to PWM flicker, especially when you turn the brightness right down (which maximizes the amount of time each LED spends in an "off" state.
That a very unscientific use of hypochondriac and it drips with contempt, which is a form of prejudice, which is a form of irrationality.
People's ability to sense traverses a wide range, and people at the extreme edge of that range are in no way hypochondriacs, rather their discomfort can be very real. And understanding that difference is not only considerate, it can be profitable. Example: ring tones most old people can't hear due to loss of high frequency hearing capability.
I'm getting older, 45, and I can hear those tones. In fact I've always been highly sensitive to high frequencies, and one of the things I always hated about CRTs was the whine they make. It gave me headaches so when LCDs came along, I got one early on -- I think I paid $600 for it, but it was such a sweet relief, that it worth it to me. Now, I'm lucky in that I don't notice any flickering, and I'm relieved of the suffering CRTs caused me, but it sounds like other people have the opposite problem. Someone who decides to not be contemptuous, is going to make some decent money, maybe a lot of money, selling them solutions for what is a very real problem for them.
What changed under Obama? Nothing Good
There are monitors out there with DC backlights...check the more technical reviews like the one mentioned in the summary.
These are also present on some high-end cars with LED tail lights. Some Cadillac Infiniti, Saab and the latest VW cars all have them.
There are high voltage regulator and amplifier tubes that can be run high enough to be useful generators, without the leaded glass getting in the way. The anode geometries are often more suited to the task too.
CRT's have been built using leaded glass for decades; about as long as color TV has been around. (with its higher typical 2nd anode voltages)
Frankly, purpose built x-ray tubes aren't all that hard to come by in the first place.
You were the kid in kindergarten that got out the protractor and protested that NONE of the shapes were the same because their corners were off by just a bit, weren't you?
I have a Dell 2407 and I run at 25% brightness. It also doesn't use PWM since it's old enough to use CCFL. At 100% brightness it is uncomfortable to look at for any length of time.
Drives me nuts. I'm so happy when I see the occasional one using DC or high-frequency PWM.
With CCFL backlights flicker was less of an issue because the backlight itself smoothed out the flickering. With LED backlights the on/off cycle is sharp and immediate and therefore more noticeable.
Also, some LED backlights drive the PWM as low as 90Hz, which can be visible when the *whole screen* is flickering at that rate.
No, they're not hard to get these days.
The books I referred to were from the '50s when the old tube a kid might get his hands on would be a B&W tube from the old TV.
However, the [point was that they are similar. The possibility to use a CRT as an X-ray tube (even if not a very good one) does tend to support that.
Yeah, some people are definitely more sensitive to it than others. I know people who had no problem looking at a 60 Hz CRT, but could never do it for more than a few minutes, as i could see the light flickering. I've never had any problems with LCD/LED displays, but I'm sure there's people with enough sensitivity in their eyes for it to bother them.
Anthropic principle: We see the universe the way it is because if it were different we would not be here to see it.
Older LCD displays used CCFL backlight, while many newer ones use LED. The LED ones show backlight flicker due to PWM much more clearly.
According to this article (http://www.tftcentral.co.uk/articles/pulse_width_modulation.htm) LED backlights generally pulse between 90-420Hz, not in the KHz or MHz range.
I'm able to see the flicker of 60Hz and perhaps a little higher than that. I'll get some massive eyestrain too if I sit at a CRT monitor with a 60Hz refresh. At 85Hz I can rarely see the flicker if I concentrate and it's relatively comfortable. Higher than 85Hz and it's much better.
I'm sitting in front of three LED backlit LCDs and they're not flickering at all. The LEDs stay on. All of my smartphones with LED backlighting haven't flickered either. The wife just got a new phone with an AMOLED display and I do see some flicker on occasion. I do see it with LED brake lights on most cars; a few of them only flicker with parking light brightness and then don't flicker at the brake light intensity.
I think jones_supa needs to change monitor manufactures.
LCD displays with CCFL backlights are less susceptible to the problem than ones with LED backlights. And some monitors use non-pulsed backlights or at least smooth it out with a filter circuit or something.
Turning up the duty cycle will reduce both the time that they're on and the time that they're off, but the ratio will remain the same.
There is a real component to it, particularly if you're a migraine headache sufferer. Migraineurs tend to be sensitive to certain frequencies of flicker. I find that fluorescent lights are uncomfortable and tiring whereas LED bulbs and incandescent bulbs are fine. Then again, I've never had a problem with LED/LCD, fluorescent LCD and CRT monitors because the flicker rates seem to be at rates that don't bother me. (Staring at highway markings close to the car at highway speed drives me absolutely bonkers, though. Good thing I don't really need to do that. :)
As someone who experiences this issue, I can confirm it exists. I imagine most people are sensitive to it at some frequency but it may not be at frequencies that are ordinarily an issue. Get a strobe light, play with it and chances are you'll find a frequency that bothers you.
Incandescents don't noticeably flicker. They might imperceptibly dim as the voltage changes but they take hundreds of milliseconds to dim completely, so the dimming and brightening is likely imperceptible.
You couldn't watch PAL content on an NTSC display, or PAL content on a PAL display? The latter will look a lot more normal than the former.
Whoa, whoa, whoa. There are disorders of the brain and inner ear that can upset the body through visual stimulus, epilepsy being one of the more common ones, but there are different forms and varying degrees of epileptic conditions. I do think that WiFi sickness is a bunch of hooey, but refresh of light sources is a known and scientifically documented problem for some people. Despite what you may think we're not all the same even though humans have the same parts. All kinds of things can go really wonky if one little genetic bit gets flipped the wrong way. I am not saying that the OP is making this up, as he very well may have a medical condition that makes him sensitive to visual stimulus, but this is definitely not a "common" problem and is something he really needs to get diagnosed properly.
The problem I have with this definition is this: how do you tell someone you literally mean something - truly, literally mean it - if you can't be assumed to be being literal when you use the word "literally"? You can't, without dancing and singing and saying way more than you need to say. There's no need to use the word "literally" if you're not being literal.
...or maybe his problem with eye strain have something to do with staring, wide-eyed, at a single object, in a florescent light, dry, air-conditioned environment for 8 hours a day while on a steady diet of diuretics like sugary caffeinated substances.
I did not see anything in the summary to indicate that jones_supa had positively identified the LED backlight as the source of his problems to the exclusion of all else.
Neuroscientist weighing in.
"Flicker fusion" is the rate at which multiple flashes appear to be a constant light. When your eyes are still, flicker fusion is in the few tens of Hz for your central vision. In your peripheral vision, it can be roughly 100 Hz (which is why old fluorescent lights bother some people, me included). The killer is when you're moving your eyes around a lot. With large eye movements, flicker fusion can be in the 100s of Hz -- high enough for the backlight to bother a small number of people. I bet DLP projectors drive you crazy, too -- on many you can get a nauseating rainbow effect when you flick your eyes from one edge to the other because of how the color wheel works.
As a side note, CRTs were way worse. When I measured one with a phototransistor and a 'scope, I was really surprised that their duty cycle is ~10%. You probably just didn't use them as much per day, or age is making you more sensitive.
Might've been mentioned before and I missed it buried in all of the posts, but I can tell you why CRTs are whining all the time.
It's because LCDs have replaced them. :)
Many CRTs and fluorescent lights (yes, even CFLs) flicker like crazy. I've swapped out a few in my house because of it. It is a known problem with video cameras, which run at similar frequencies to the human eye. Why would so many of you deny that this is possible for some people?
One maddening thing that people seem to miss is that the flickering from PWM is NOT at the same frequency as the PWM.
Say you are running PWM at 100 hz. at 50% brightness, your light is flickering at 50 hz. At 10% brightness, your light is pulsing at 10 hz.
This easily explains why LED flicker can be visible (to those sensitive to flicker) even when PWM is hundreds of hertz.
Speaking personally, I suffer from migraines and am exceptionally sensitive to flickering light sources as a trigger. This happens even at frequencies much higher than those that trigger photosensitive epilepsy. Flame away if you think this is psychosomatic. I wish.
That said, I have noticed very few LED-backlit monitors that suffer from flicker issues at normal brightness. And I *can* detect flicker from many LED sources such as brake lights, traffic lights, and flashlights that use PWM, and especially things run off mains power at 60 hz (intolerable) or rectified "flicker free"120 hz (still pretty intolerable, since the lights still cut out at the crossover point).
I'd also point out that migraines are pretty distinguishable from regular headaches, and (for me and many) also have a significant nausea-related comment, so while the OP may be sensitive to flicker, his symptoms sound more like normal eyestrain.
Yeah... until it's /your/ IPod which gets stolen!
CLI paste? paste.pr0.tips!
So do LEDs bother your eyes? I think CRTs gave me headaches far more often than has any form of flat panel display, at least partly because of the whining noise that CRTs emit. No. You're imagining things. But, that being said, you're not alone. I heard somebody walk into the retail establishment that I work at and said, "I'm disappointed that you guys installed automatic doors that emit so much radiation, but I'm glad that at least you don't have horrible fluorescent lights that would make me unable to shop here." Of course, she was saying that standing under about 500 CFL's that she assumed weren't fluorescent because of their size, shape, and color.
If you've never heard a CRT whine, just get one of any quality, a computer that will let you set the vertical and horizontal refresh rates (linux works!), and try out a few configurations that aren't supported. I find at least a third of the settings will give a nice whine, even some of the ones that look okay. Once you've determined that this hardware that depends on oscillations to perform its designed purpose can impart those oscillations to the air around it, maybe you'll believe that a lower-quality CRT can do that even when running in approved configurations.
One little warning. Don't do that test very long with your favorite CRT. As with most things used in a manner that's out of bounds of the engineering specifications, bad things can happen. Also, why do you still have a favorite CRT?
Sure I'm paranoid, but am I paranoid enough?
If I am well rested and eat a good breakfast, I can move small objects with my mind. So there.
That's pretty much my problem too. I can just picture someone on trial for murder testifying "yeah judge, I literally murdered the victim."
Judge: Guilty!
Defendant: I meant definition two your honor.
Judge: Well that's bad
Defendant: Uh, is that the good bad or the bad, bad?
For the WIFI people there are strong indications it is psychological only. For the flicker-sensitives, it has been known to exist as effect since movies exist. The original cinematic 24 pictures/second was selected because most people cannot see that flicker or are not bothered, but it is known that some can and may even get headaches, etc. The problem is really not new, just the place it turns up in is. So, we can say scientifically that some LED backlights may have that effect on some people. Of course, this would require rather low PWM frequencies, for example because an old CFL design was just adapted, where the slow CFL PWM is used for LEDs. CFL inverters run somewhere in the 50-100Hz range and their PWMs are synchronized to that. If you use the same PWM for LEDs, some people will see flicker. CFLs are pretty sluggish, leaving only minimal flicker, while LEDs are fast.
Of course, if you design for LEDs, you can run the PWM at > 1kHz, and there nobody should see any flicker. Ideally, you can run it at > 50kHz, then nobody can hear anything either.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
I don't understand how the carrier frequency is chosen in consumer goods
I do. I write firmware that does backlight PWM for a living (among other things).
Everyone used to do high frequency flicker-free PWM, in the kilohertz range. Then they noticed that you can improve the motion handling capability of an LCD panel but flickering the backlight at the same frequency as the screen refresh. It's kind of like how a CRT's phosphors fade and thus flicker at the refresh rate. Turns out it stops LCDs blurring with motion too.
In practice most monitors do both. They use high frequency PWM to set brightness and then switch that on and off at a low frequency like 60Hz. This is what causes the annoying flicker, but hay, at least the crappy review sites can say motion reproduction is better than the competition.
const int one = 65536; (Silvermoon, Texture.cs)
SJW, n: "Someone I don't like, and by the way I'm a fuckwit" - AC
Incandescents don't noticeably flicker. They might imperceptibly dim as the voltage changes but they take hundreds of milliseconds to dim completely, so the dimming and brightening is likely imperceptible.
Quite right. You can measure the flicker though, but it is really small due to thermal sluggishness.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
PAL flickers at 25Hz (two half-images are used). And traditional CRT TV screens already provide significant dampening. LEDs provide no dampening at all.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
Sure there is: sarcastic over-emphasis.
Actually, your run-of-the-mill red LED has no problems going up to 100kHz or so. White is supposedly slower because of color conversion. And IR LEDs used for network connections (in a GBX, for example), do > 1GHz.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
It actually burns me up when I hear it
It literally burns me up too.
My pants are on Fire!!!! Why does this keep happening!!?!
It makes dashed lines, rather than solid lines, in the afterimage. For ME the dashed lines don't bother me, but the original flickering does.
This is just a solid state ballast. But they need to run them at something like 30kHz instead of 50-60 Hz (WTF in a car).
now we need to go OSS in diesel cars
Or more accurately, the highest frequency that someone can see flicker varies widely among the population. The effect is not in the retina, but in the brain. It seems to be a function of the speed of the brain.
now we need to go OSS in diesel cars
Ah, the good old "it doesn't happen to me, he's a liar" reasoning.
There are enough examples of the placebo effect that this reasoning is a fair place to start. If you claim to observe an effect that most people cannot, you need to produce data that shows you can discriminate the effect under blind conditions. Otherwise we have no reason to believe you are any different from EM hypersensitives, etc.
Give me Classic Slashdot or give me death!
Yeah about as serious as running out of ding dongs.
Don't worry, Slashdot has an endless supply...
PWM frequencies are usually chosen as a trade-off: Too low frequencies mean flickering, audible noises, and, depending on the application, larger caps/coils. Too high frequencies mean higher CMOS switching losses, and RF signals emissions which may violate regulations.
The WLAN frequency was chosen as the resonance frequency of water because due to absorption that frequency is basically useless, so nobody really wanted it.
Actually some people might notice things that others don't. Most LED tail-lights drive me absolutely crazy, but my dad doesn't even notice them. Same for sounds, the old TV in our bedroom has a high whine that only I can hear, my girlfriend can't hear it, and thinks I'm crazy since I unplug the TV before going to bed. Same for flourencent lights, some people can see the flicker from crappy ballasts, some are oblivious. People have different sensitivity to frequencies at the edge of perception, some people won't notice it, and some will. Welcome to normal human variation.
I recently went shopping for decent IPS displays, and most of the LED ones do noticeably flicker at low backlight levels. Some, cheaper ones, were tested with noticeable flickers at all levels. I picked one that still used tubes, since I generally work with low brightness levels (for print work), and even decent LED monitors started flickering there (and its hard to get a good, wide gamut, monitor with LEDs and not break the bank).
A patriot must always be ready to defend his country against his government. -edward abbey
The differences between a CRT and an x-ray tube are not at all subtle.
Damn, there are differences between an x-ray machine and a TV? Maybe internet trolling is not your calling, perhaps you could become a detective!
OK, they both have filaments to boil off electrons and both use a high voltage to accelerate them, [towards a target]
The electrons accelerate through the tube towards a target, which in the case of an x-ray tube is a metal plate, and in the TV tube is a metal mesh. The accelerated electrons interact with the atoms in the target and excite their electrons to higher quantum states. When the excited electrons return to their stable state, a photon is emitted. Lower energy transitions produce a photon in the visible spectrum, while higher energy transitions result in x-rays. Transition size is mostly dictated by the energy of the bombarding accelerated electron. Thus, the only real difference between a CRT and x-ray tube is plate voltage.
If you do a quick web search you can easily find out just how different they are.
My suggestion for you would be to take a physics class.
Flicker on a CRT was typically at 25/50/75/100Hz, 30/60/90/120Hz. At or above 50Hz, flicker was usually not noticeable or a problem except for sitting very close to very large screens (because flicker gets noticed faster in our peripheral view). If you get serious headaches from 50/60Hz flicker, you should get headaches from ANY non-solid-state artificial lighting (incandescent, fluorescent, halogen, ...) because the net operates at 50/60Hz and thus these lights go dimmer/brighter at that frequency (not on/off because there is an afterglow (heat)).
LED PWM generally sits at a carrier of ~1kHz and can easily be as high as 1MHz for consumer grade (there is actually an increased cost for lower frequencies as the capacitors and coils are larger), this is well outside the range that our brain can notice or process. You should have more issues with displays that have non-LED backlight because they could be at a low multiple of the net's frequency.
Custom electronics and digital signage for your business: www.evcircuits.com
And insecticide and iced tea both contain water, yet they aren't really very similar, are they?
It is more like comparing Pyrethroids to Neonicotinoids.
One is designed to produce short wavelength radiation, in abundant quantities, and the other is designed to produce meaningful, controllable patterns of light and just happens to produce a very minor amount of X-ray radiation.
But the ratio of visible/x-ray radiation is determined solely by electron voltage in either tube. You have very shrewdly deduced that CRT tubes are designed not to produce x-rays by careful plate voltage selection, but realize that is the only thing. With a different transformer and higher plate voltage, the CRT would shoot out x-rays just fine.
Do you mean GBIC? I'm not aware of them using LEDs. For optical GBICs lasers are used (usually VCSELs - or they were when I last cared about the internal workings of fibre stuff, which was about 10 years ago ).
Does reviews that include assessments of PWM in monitors. Very recommended.
http://www.tftcentral.co.uk/
You were the kid in kindergarten that got out the protractor and protested that NONE of the shapes were the same because their corners were off by just a bit, weren't you?
And don't even get him started about the sub-atomic particles being in different places....
Benq is in the process of introducing non-PWM flicker free backlight LED monitors.
http://www.tftcentral.co.uk/news_archive/28.htm#benq_bl2710pt
have too many children because you don't about contraception
Doesn't matter; had sex
No, there's an exponential amount of people that agree with you.
Confucius say, "Find worm in apple - bad. Find half a worm - worse."
I'm always amazed at how many people think that there is a lot of variance in physiology. like they have super-fast rods and cones. is this just a generally harmless form of psychosis? I'm not arguing that mutants don't exist (http://en.wikipedia.org/wiki/Tetrachromacy, or the myostatin), or that training can make you very sensitive to, say, perfect pitch. just that this topic (and related, such as wifi allergy) seems to attract remarkable delusions (imo) of grandeur.
I could care less if you're frustrated by that.
What doesn't kill you only delays the inevitable
Really? Because people have been using "actually" correctly for a long time, and there's no evidence whatsoever of it growing a new, sarcastic meaning. How would your use of the word suddenly affect the world when everyone else's use (including mine) has not done so in all these centuries? Big ego much? (And even if it did, so what? People are remarkably good at resolving ambiguity.)
Also, referring to the metaphorical use of "literally" as misuse simply proves that you do not know your own language! Because it's not misuse. You might as well claim that using "terrific" to refer to something that doesn't cause terror is misuse. The language has changed since the 1600s (which is how long it's been since "literally" started being used metaphorically). We don't talk like Shakespeare any more. Get over it. Forsooth isn't coming back, and neither is your precious only-one-meaning version of literally.
What people who complain about the metaphoric version of "literally" mean is "ooh, I have a (false) factoid I can dangle to demonstrate my intellectual superiority!" Of course, to anyone who has the wit to open a dictionary, it actually proves the opposite. You know less about your own language than that semi-literate teenager whose perfectly correct usage annoys you so much.
When I meet someone who complains about so-called misuse of "literally", I know I've met my intellectual inferior. And damn straight, I'm smug about it! :p ;)
I remember having headaches and eye strain after getting my first LCD monitor. Thinking back I'm wondering if the monitor was passive matrix all recent monitors don't bother me though.
Ah, yes. Has been some time here too. You could argue that a laser diode is just an LED with a bit of extra filters (which admittedly is a gross simplification). The "laser" part is not for speed, but for avoiding different travel times of different light frequencies. In principle, laser diodes should switch slower than LEDs.
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
So I can only say it when I speak then? :)
If "she" had a knob I'm sorry to tell you this but....
Snowden and Manning are heroes.
You'll find the same problem mentioned by flashlight modders (candlepowerforums.com, budgetlightforums.com) -- some multi-level lights have quite annoying PWM.
GLOSSY bothers me more. Too much reflection, not even talking about fingerprints. In a way, a glossy screen is going back to a cheap CRT.
I've got better things to do tonight than die.
I can eliminate PWM on some of my monitors by setting the brightness to maximum and lowering contrast and the color levels. When I watch those monitors for a full day, my eyes are OK. When I watch my laptop (240 Hz PWM) where I can't eliminate the flicker, my eyes are tired by the end of the day.
When I first learned about how LCDs are made, I was furious that after all the problems with CRT monitors, LCD makers resorted to such a poor choice. The world my eyes see is flicker-free. Why should monitors be different?
The technology for flicker-free LCDs exists and it's called calibrated color level compensation. It should be the standard.
I kinda need both my eyes until the end of my years, so I'd appreciate it if manufacturers stopped wearing them out with PWM...
It makes dashed lines, rather than solid lines, in the afterimage. For ME the dashed lines don't bother me, but the original flickering does.
This is just a solid state ballast. But they need to run them at something like 30kHz instead of 50-60 Hz (WTF in a car).
if it's brake lights they may have ran studies that they get noticed better this way.
world was created 5 seconds before this post as it is.
Physically hack the monitor get some light blocking film or use sunglasses.
Techno hack the monitor to do current dimming rather than PWM dimming. This of course will screw the colors to hell and gone.
Techno hack the monitor's LED backlight array so you can turn off some of the LED or replace the LED array with something not as bright or with more LEDs and the ability to turn them off individually.
Techno hack the monitor's LCD backlight by placing an LCD shutter over the LED and use that to dim it.
Or you can go whine about it on slashdot.
*Techno hack, sorry about that but I felt the real term was too rich and nuanced for the author.
I'd go on a Vegan diet but the delivery time from Vega is too long. --brownkitty
Here we go again (same discusion on Slashdot several years ago). Everyone can see 24 Hz. flicker. I seriously doubt there is anyone on earth that cannot. This problem was solved long, long ago by flashing each movie frame on the screen 2 or 3 times, then switching to the next frame. 3 x 24fps = 72 Hz. This corresponds perfectly to the fact that, for most people, a CRT refresh rate of 72 Hz. or so is comfortable. For example, the Eumig S710D Super 8mm film projector from the 1970s has a 72Hz. refresh rate due to its triple-slotted shutter.
I see the same issue with plasma monitors. The phosphors used to have a long enough decay, so a 60Hz refresh used to be fine. But manufacturers have been moving to phosphors with a much shorter decay time to avoid ghosting and other issues when you have a high contrast object moving across the screen. So now most late model plasma monitors remind me of some of the first SVGA monitors that came to market.
Can I have a 120Hz screen refresh, please? Europe solved a similar issue with PAL CRTs decades ago by boosting them to 100Hz.
I think the problem is that the Flicker Fusion Threshold might be poorly understood by manufacturers.
I think lots of factors affect our perception, young people can perceive flicker more than older people, and things like caffeine can make flicker more noticable.
But why do you sound so resentful and disbelieving of the claims? If he is right and it bothers him but doesn't bother you, what negative things are you gonna have to suffer from to accomodate him? I don't get when people shout down stuff like this. It is a known phenomenon and it only affects a small portion of the population. What's in it for you to prove him wrong?
Well you said it was Excel, so....
Try a different spread sheet.
Sig Battery depleted. Reverting to safe mode.
As someone with this problem, yes! Surprisingly setting the backlight to 100% pretty much eliminated my eye/migraine issues from upgrading to 3 BENQ 2250s. A SOLUTION to the brightness that worked very well for me was automotive window tint film (nothing special, $10 from O'Reilly) on plexiglass panels. I thought the image quality would be toast, but everything is perfectly clear and easier on the eyes now.
I've been using CRT monitors since 1993. I can stare at them all day long as the refresh rate is 75 Hz or higher. At 60 Hz, my eyes get tired out pretty quickly.
As for LCD monitors, I bought one years ago for home use and had to sell it off on Ebay months later when I realized it was giving me eye strain (the effect is noticeable after a few minutes... strain at the temples). For the next 7 years, I avoided LCD monitors when possible, eventually becoming the last person in a 100+ person office to use still CRTs (since I didn't want to give them up at work or home). Even kept using CRT TVs. My theory at the time was fluorescent back lighting was the culprit, since fluorescent lights gave me similar eye strain. To my horror, I got a LED backlit LCD monitor at work and still got the same headaches/eyestrain.
Then one day I realized I was looking at my cell phone screen all the time with zero eyestrain (HTC Incredible, original version as when first released). I was puzzled, until I read that this particular model uses AMOLED display, which is different than normal TFT displays, since the pixels themselves provide the brightness.
Next, I searched to find a test which could stimulate my eye strain pretty quickly. Behold, the test: http://www.lagom.nl/lcd-test/inversion.php
This test creates eye straining flicker for me on regular LCD displays, but not on CRT and AMOLED displays. Hooray. Given this test, I've found some LCD laptop displays to be more bearable than others. For example, Apple Macbook Air (circa 2012) does pretty well on most of the Inversion Walk tests, but not all. My Dell Latitude E6430 (2013) does even better. So good, that I can use that laptop most of the day with its built in LCD screen. Hopefully I'll eventually find a LCD desktop monitor that does well with the Inversion Walk tests. In the meantime, I dream of color e-ink with fast response times, or an affordable AMOLED monitor.
On a side note: older compact fluorescent bulbs gave me similar eye strain. Seems the newest generation of bulbs are bearable, so hopefully I don't have to hoard 60 W incandescents if/when they are banned.
But if they were blind, how do they seen the flicker? :D
Finally a good reason to be an insensitive clod!
I can easily see the flashing of PWM driven LEDs as used on cars, to the extent that I can identify the brand of a distant car at night purely from the speed of the flicker of the taillights. I can also easily see the flicker of my Galaxy S3 screen, especially at night. During the day I can easily see the flicker of LED DRLs. :(
Whatever way my vision works, I often end up gaining detail from a quick scan of my eye's focal point around what I am concentrating on. When a PWM-driven light source is in my field of view I see it as a trail of distinct dots, where a continuously driven light would appear as an evenly illuminated streak. Maybe it's just because I've got a lot of practice of looking at things from 30 years of observational astronomy so I am used to getting the best from my mk1 eyeballs
Cinemas are often painful as I can very easily see individual frames in panning shots, even with the motion blur on the individual frames. Motion blur annoys me as my vision system can't figure out if it is out of focus or blurred, so my eyes get very tires from certain films
Back in the CRT days I could easily differentiate between 85hz and 100hz monitors, and I could identify whether a game was operating at 100hz or 120hz if the monitor framerate was higher than that. Mostly by being able to see each frame when the POV was changing quickly, and I could gauge whether there were 8 or 10 frames used for a rocketjump and that kind of thing. This led me to having to spend real money on decent monitors that I didn't see the flicker on.
Newer flat panels have light sources that are a lot more steady, and that never truly drop in brightness as there is no longer an active scan in progress. These no longer flicker as much as older monitors did.
Ophthalmologists didn't find anything odd with my eyes at that stage, it was just my having a particularly discerning vision system. Lucky that I have, as I've located drusen on my retina that I've spotted early enough to possibly be useful in any treatment of this precursor to macular degeneration. Sucks, but I'm still in my 30s so worst case I have more time than most to get used to using peripheral vision for daily tasks.
- This sig deliberately left blank. Nothing to see, move along.
Laptops have fairly wimpy backlights.
My desktop monitors are insane at 100% brightness. Great for reading it from 100 meters I suppose but from 2 feet it can be painful.
Hell even this mostly white slashdot page at 75% brightness is slightly uncomfortable.
Bit odd. I know for a fact KDE has brightness control included.
My Dell also has a hardware brightness key combination. FN + Up or Down arrows.
The awesome thing is KDE knows when I use the hardware keys. Perfect example of not shoving propriety crap in to a laptop.
Its not you are lying. That implies you know you are doing it.
The most sensitive eye can not see anything anywhere near 100Hz.
If you have seen PWM less than about 400Hz I'd be extremely surprised and generally it is in the kHz range which if anyone says they can see flicker is bullshitting badly.
You simply cannot buy PWM controllers which go low enough - pretty much all generate their own clock btw since precision isn't required.
Remember audiophiles say that good expensive cable sounds better when they are listening to coat hangers. Same thing.
Physics. The human eye cannot see hundreds or up to hundreds of thousands of Hz.
It just isn't possible therefore the guy is an idiot.
Grab an arduino, hook up a bright led, a pot and make it output via serial what Hz the pot has selected.
Then blink the LED at that speed. You can test it yourself.
I'm surprised no one here has mentioned DLP projectors. You know, the ones that use light reflected off a DMD and passed through a rotating colour wheel to produce a red, then a green, then a blue, then a white picture.
Those things drive me crazy. I'm fine so long as I sit sufficiently far back with my eyes motionless, looking at the centre of the screen, but if I move them even slightly, the rainbow effect becomes painfully clear.
This seems to be yet another negative side-effect of those of us with high-frequency light perception.
"Nine times out of ten, starting a fire is not the best way to solve the problem." - my wife
Erm wouldn't the logical conclusion be to use a multiple of the refresh rate, not the refresh rate its self?
E.g. PWM of 3kHz would do the exact same effect you just described while also maintaining that effect for both PAL and NTSC sources.
Most LED tail-lights are fine, but certain auto-makers have apparently decided to make theirs insanely bright and/or use low refresh rates. *cough* Audis, Mazda 3's, mid-2000 Honda Accords, etc.
I'm not Corey Hart and I don't want to wear my sunglasses at night....so I can, so I can...get through my damn commute without getting a migraine in stop and go traffic.
No, pal has a full-frame at 25Hz. But it scans the full size of the screen at 50Hz on alternating scanlines, this has the effect of reducing the flicker to next to nothing due to the persistence of the phosphors
The effect that you saw could be related to the RGB subpixels.
YOUR eyes can't see it. Mine can't either. We know that some people can though. To admit that though, would shake the foundations of your beliefs, much like religion "revelations." There is most likely a perfectly valid reason that this phenomenon exists and we just don't know what it is yet. If you accept that some people have problems with certain frequencies, that doesn't mean you have to throw all of physics out the door.
:)
Oh and I did that experiment years ago with a 555 timer. You can take your arduinio with you when you leave my lawn
"Ah, the good old "it doesn't happen to me, he's a liar" reasoning. ...Rates that that drive me crazy don't drive everyone else crazy."
Ah, the good old "I am special" reasoning.
My guess is your eyes hurt because you suppress blinking while looking at the computer screen. When people watch things interesting they do not blink as much. Your eyes dry out and they hurt. Your eyes cannot physically respond to fast blinking. Its called persistence of vision. Once the blink rate exceeds that there is no physiological response. If you think there is you are fooling yourself. I once had a guy who said he could hear a 20 khz signal in a drive motor circuit. I would turn on the power and He would grab his ears. Problem was is that the power supply was unplugged. Either he was trying to fool me or he was fooling himself. What you should do is set up an experiment. Set up a pair of computer controlled LEDs to flicker at different rates then guess which flickers faster. Have the computer randomly change the rate and which one is faster. Then see at what flicker rate the error rate goes to zero. That is when you can actually see the flicker.
Got a citation of a double blind study showing someone detecting anything over 100Hz?
Cause without that, we know nothing of the sort.
You overestimate the amount of attention anyone pays to you and your goings on.
I can see flicker of LEDs well over 100Hz. I work with them and build LED devices all day long.
Still waiting on Serviscope_minor to wake up to fucking reality and realize that Jessica Price isn't going to fuck him.
You citation needed folks get on my nerves, but in my line of work the saying is "show me the data." I have alot of free time so I went ahead and googled it for you. Now most of the studies are behind paywalls and the wiki articles all allude to the problem. You however went ahead and thought you were being clever by quantifying anything over 100Hz. As I said, most of the wiki document alluding to it were behind paywalls but I did find ONE that has a number in it. It's a PDF and it is on slide 2. Go read that and holler back at me. Once you have your revelation, you can accept it as a fact that doesn't mean the end of all physics, or you can move your goalposts some more.
From the DOE
Also for your perusal Go to the lighting section.
Here is one of the offending paywall studies. The synopsis says there is some negative effects but it didn't have that magical 100Hz mentioned and I'm not paying to find out- I already know.
My response sounded pretty dickish. I have bad communication skills. It's a problem I know. I'm not trying to be that way and I'll tell ya why.
The citation needed shit get on my nerves because, like I said at the end of the post, I already know. Being skeptical seems to be one of those new hipster douche fads. Skepticism is good but these days you can't claim the sky is blue without someone screaming for a citation. One could respond that I don't know shit but I have already studied this subject years ago. That person is the one that doesn't know, they need to educate themselves- ya know be all bootstrappy and stuff. So say someone makes a claim that GWB was caught having sex with a goat and it's on youtube. When I hear something preposterous, I too get skeptical but you know what I do? I go look on youtube. If I can't find that info, then I can come back to the discussion and start asking for citations. Citation needed has been relegated to a synonym for "shut up" and I don't like it.
>100fps or so is way above the threshold of about 20 frames per second
Bullshit. Period, full-stop, boldface, italicized, and surrounded in BLINK tags.
Your corneal surface isn't equally sensitive to flicker. Rod-dominated peripheral vision is several orders of magnitude more sensitive to motion and flicker than cone-dominated foveal vision. In terms of framerate or high-contrast flicker, the magic point at which literally nobody can tell the difference between N and 2N (where "N" = "framerate in hertz") regardless of which part of the eye it strikes, its brightness & contrast, and the amount of frame-to-frame change, is somewhere around 400fps/Hz (slightly more for some, slightly less for others). Now, you don't literally have to go quite THAT high to have a satisfactory viewing experience with most content, but if you really want to split hairs and look for edge cases where people can reliably tell the difference in double-blind tests... that's approximately where it is. WAY above 20fps.
The ONLY reason why 24fps (motion picture film) presents any kind of illusion of motion is because film's analog nature encodes additional higher-order information into it in the form of motion blur and other artifacts. I can guarantee that raw, razor-sharp blur-free high-contrast 24fps video is VERY unpleasant to watch, even if you independently take care of flickering so it appears as a sequence of sequential solid images.
And yes, somewhere between 5-20% of the population (slightly lopsided towards males) ARE more sensitive to flicker. It's been studied, documented, and quantified. The number is well known to monitor manufacturers... they just don't care. The best we can hope for is some future backlight ASIC whose behavior can be tweaked by end users via I2C, even if the manufacturer of the monitor itself doesn't lift a finger to support it. Then some bean counter in management will decide he can shave 1.7 cents from the manufacturing cost by omitting the pullup resistor needed for the I2C bus to work, and we'll be fsck'ed again.
^^^ Argh. replace 'corneal' with 'retinal'. It's late.
Cornflakes and Ricebubbles?
No, it has to be the same as refresh rate, or you get PWM artifacts:
http://www.blurbusters.com/faq/lcd-motion-artifacts
The best implementation is called LightBoost -- PWM at one strobe flash per refresh, for the CRT effect
http://www.blurbusters.com/faq/60vs120vslb (60Hz versus 120Hz versus LightBoost).
Also TFTCentral's "Motion Blur Reduction Backlights Including LightBoost" article:
http://www.tftcentral.co.uk/articles/motion_blur.htm
You ideally need PWM >10000 Hz.
- http://opensiuc.lib.siu.edu/cgi/viewcontent.cgi?article=1538&context=tpr (500 Hz detected)
- http://www.lrc.rpi.edu/programs/solidstate/assist/flicker.asp (300 Hz detected)
- http://www.lrc.rpi.edu/programs/solidstate/assist/pdf/AR-Flicker.pdf (10,000 Hz detected)
The last one has a rather interesting diagram where PWM, in certain cases, up to 10,000Hz, is detected via a stroboscopic / phantom array effect (not too different from wagon wheel effect).
This is true, 10Khz is detectabable, agreed by this paper
- http://www.lrc.rpi.edu/programs/solidstate/assist/pdf/AR-Flicker.pdf (10,000 Hz detected)
The last one has a rather interesting diagram where PWM, in certain cases, up to 10,000Hz, is detected via a stroboscopic / phantom array effect (not too different from wagon wheel effect).
For those people who don't mind CRT's, but get eyestrain from motion blur instead, there's a new technology called LightBoost (google "LightBoost") which is essentially PWM at one strobe per refresh, with 92% less motion blur than regular 60Hz LCD (full order of magnitude less motion blur).
Competition gamers have been purchasing 120Hz computer monitors as of late, and enabling the LightBoost strobe backlight, to regain CRT like clarity; covered at the Blur Busters Blog - http://www.blurbusters.com/ -- which also has 60Hz versus 120Hz versus LightBoost comparisions available.
And TFTCentral's "Motion Blur Reduction Backlights Including LightBoost":
http://www.tftcentral.co.uk/articles/motion_blur.htm
They found that LightBoost greatly outperformed scanning backlights.
Obviously, this technology is not for flicker sensitive people, but it can be turned on/off, and it's another option on the market.
Dear AC,
Please explain how ocular scar tissue can affect persistence-of-vision effects in any way, shape, or form.
I'm all eyes.
Kid-proof tablet..
Can't be building them very well if you are PWMing around 100Hz.
Try 400Hz - 15kHz and you products might work better.
The whine you hear is loose transformer winding(s). On a CRT, it's the flyback transformer. On an LCD, it's part of the power supply. Some of them do it, some of them don't.
(When I was much younger, I could hear flyback transformer in every CRT TV -- even at some distance. I could be just walking down the street on a cool summer night, localize the sounds emanating from open windows, and count the various different televisions that were on inside of a house using my ears alone. After a bunch of subsequent years of concerts and loud music and playing FOH engineer, I can't do that anymore, which might be a pity, except: My evening walks are MUCH more peaceful now.)
Kid-proof tablet..
Anybody heard of a low-pass filter? Smooths PWM out very nicely.
See, i buy LCD's knowing that 800nits is daylight-visible-bright. I also don't buy screens advertising over 10k:1 contrast. While they look great, they hurt your eyes. So my 300nit, 3000:1 20" LCD isn't Apple Cinema picture quality, but, it's perfect for autocad.
As an electrical engineer, i know the formulas. The 10pF cap would not maintain the LEDs, i know. It would, however, smooth the attack of the flicker. So even tho it would still be flickering, it would be far less noticible. Also, yes, a small amount of power would be consumed, but a good tantalum / high quality film cap would minimize this.
Were you aware that extra strength placebos are more effective than regular strength placebos?
Competition Good, Monopoly Bad.
Charging a 10pF cap will consume less power. That's a fact. And since i deal with PWM every day, i'm going to say, yes, it will help.
You can't be serious. Have you ever seen an X-ray tube? Not even remotely close to a CRT in appearance, construction, or function.
Here's a description and illustration of a typical X-ray tube: http://www.xradia.com/technology/basic-technology/sources.php
And here's a CRT: http://images.yourdictionary.com/cathode-ray-tube
See the last sentence: http://en.wikipedia.org/wiki/Flicker_fusion_threshold "Display refresh rate Computer CRT displays usually operate at a vertical scan rate well over 60 Hz (modern ones are around 100 Hz), and can thus be considered flicker-free. Most people do not detect flicker above 75 Hz. Other display technologies do not flicker noticeably so the frame rate is less important. LCD flat panels do not seem to flicker at all as the backlight of the screen operates at a very high frequency of nearly 200 Hz, and each pixel is changed on a scan rather than briefly turning on and then off as in CRT displays. However, the nature of the back-lighting used can induce flicker - LEDs cannot be easily dimmed, and therefore use pulse-width modulation to create the illusion of dimming, and the frequency used can be perceived as flicker by sensitive users.[6][7]"
They both are vacuum filled glass tubes. They both have filaments to boil off electrons and both use a high voltage electrical field to accelerate them towards a target. Electrons accelerate through the tube towards this target, which in the case of an x-ray tube is a metal plate, and in the TV tube is a metal mesh. The accelerated electrons interact with the atoms in the target and excite their electrons to higher quantum states. When the excited electrons return to their stable state, a photon is emitted. Lower energy transitions produce a photon in the visible spectrum, while higher energy transitions result in x-rays. Transition size is mostly dictated by the energy of the bombarding accelerated electron. Thus, the only real difference between a CRT and x-ray tube is plate voltage.
You shrewdly point out that they have a different external appearance. The x-ray tube is (obviously) also missing the beam steering plates and phosphor used to generate a picture. Still, at the core of each device, the physics are identical in many more respects than most people realize. If you want to know more about the physical world, you might consider reading a good physics text instead of searching google images.
You're right about the whine.
And I have no issues with incandescent bulbs. They don't flicker like CFLs do (and they're far more innocuous to discard), and they don't pollute the amateur radio bands like I've recently discovered that LED bulbs do.
http://itre.cis.upenn.edu/~myl/languagelog/archives/002611.html
Examples from the 1760s, posted by Prof. Ben Zimmer.
You can use words like "really" or "actually", which don't feature the polysemy of "literally".
For now, until they get polysemous themselves. Better if words don't become that way with which to begin.
"And with his eyes he literally scoured the corners of the cell..." -- Vladimir Nabakov, Invitation to a Beheading
"the wretch did not make a single remark during dinner . . . whereas I literally blazed with wit." -- William Makepeace Thackeray, Punch magazine
"Lily, the caretaker’s daughter, was literally run off her feet." -- James Joyce, Dubliners
"‘Lift him out,’ said Squeers, after he had literally feasted his eyes in silence upon the culprit." -- Charles Dickens, Nicholas Nickleby
"Literally, I was (what he often called me) the apple of his eye." -- Charlotte Brontë, Jane Eyre
"Every day with me is literally another yesterday." -- Alexander Pope, in a letter to Henry Cromwell
Now, ask me which hypthesis I find more plausible: that all these well-respected gentlemen and ladies of the arts are actually idiots? Or that some random anonymous slashdotter who claims that "the dictionary is wrong" is an idiot? I'll give you three guesses, and I hope that'll be enough... :)
I found programming 2 feet away from a drum being pounded constantly very effective to promote earring loss.
Tomorrow is another day...
OK, you win! A CRT is just a glorified X-ray tube!
As someone once said, "never argue with an idiot- they will drag you down to their level and beat you with experience". Your experience has defeated me. Your kung-fu is the best! Well played!
OK, you win! A CRT is just a glorified X-ray tube! As someone once said, "never argue with an idiot- they will drag you down to their level and beat you with experience". Your experience has defeated me. Your kung-fu is the best! Well played!
My comment in the first place was tongue in cheek at best. Why do you need to come and say, "ONE OF THESE THINGS IS NOT LIKE THE OTHER"? Probably nobody will ever know besides you. Either way, I was just trying to help you understand a joke that went sailing--whoosh--right of your head. That way, you might have learned something useful and interesting while also being slightly amused.
I suspect that your primary amusement is being a dickhead on the internet, so at least you are having some fun that way.
No, CRT (televisions in particular) really do make a high pitched whistle, and some of them can be quite loud. It's 15kHz more or less for a TV, and comes from the flyback, and is audible to much of the population. Whether it annoys you or not is dependent on the person, I just tune it out.
Oolite: Elite-like game. For Mac, Linux and Windows
It appears similar technology is being introduced for office lighting, with disappointing results.
I'd sort of doubt that. Solid state fluorescent ballasts usually switch at 20 kHz or more (to keep the magnetics from whistling in an audible range). Dimming is accomplished by PWM this frequency.
Its possible that some cheap crap ballasts don't have the energy storage to 'coast' through the 50/60 Hz zero crossings. Or your office might have seriously low voltage on the lighting circuits.
Have gnu, will travel.
If the backlight uses 'white' LEDs, these are actually phosphor-coated blue or near-UV LEDs, and have persistence. That said, just like a an old fluorescent tube, a driven phosphor light source has very perceivable flicker at 60Hz. 85 Hz is higher than most of the population can detect, although there are a few people who can perceive 100 Hz flicker.
Mission: To provide products that consume time and energy as entertainingly as permitted by the laws of thermodynamics.
I build them just fine because I use constant current drivers like a real LED device engineer.
China, OTOH....
Still waiting on Serviscope_minor to wake up to fucking reality and realize that Jessica Price isn't going to fuck him.
The phenomenon is real, at least for the ability to see and be annoyed by "relatively" (below a a kHz or two) low frequency PWM. I'm one of "those people" who see the DLP rainbow effect and PWM-dimming car taillights and backlights (they don't make me sick or anything, but it's a bit distracting). That said, I have never, ever seen detectable flicker from a CFL bulb. (Most likely they are usually running at ultrasonic frequencies so that the tiny magnetics inside don't emit audible buzzing. Phosphor glow probably doesn't hurt either.)
Caveat Emptor is not a business model.
It's real to the sufferers. When I started playing games for a long time on my iPod touch, I started getting blurred vision and watery eyes if I stared at the screen for too long. The problem was somewhat less if I looked at the screen for only less than a minute. And I didn't get this problem staring at an older iPod (which was LCD).
When I searched the web for this issue, I found a thread at discussions.apple.com about many Apple fan boys returning their new MacBook Pro because it hurt their eyes. I thought I was crazy until they generally came to the consensus that the eye problems had something to do with LED laptop screen. I'm not sure whether it's only PWM, but one thing's for sure, these LED screens are unpleasant to look at and have worsened my eyesight. LCDs on the other hand have a cool feeling and don't cause any discomfort or harm vision.
I gets worse -- LCD screens are being phased out by manufacturers and are being replaced by LED screens because they have better picture quality. I hope any company incorporating LED screens into their products fully investigate this issue and offer LCD screens as an alternative to LEDs. LCDs have a duller yellowish hue, but it's better than suffering eyestrain, headaches etc.
Just in case anyone is interested, this is the Apple thread discussing LED eye strain
Good to know I'm not the only one who experiences this.
"Nine times out of ten, starting a fire is not the best way to solve the problem." - my wife
You could build a small tester using one of the ultra small arduino boards.
Maybe a coin cell, switch and phototransistor plus some leds for output.
Code it to show on the LEDs what the pulsing light frequency is.
Under 100Hz, 200Hz, 1000Hz etc.
Then if you see a product you like you can easily check what the PWM frequency is before you buy it.
Remember to do the check with the brightness set to min. Max brightness is often 100% duty and will have zero flicker.
Lots of LED bulbs are no-name Chinese imports. That they accept and operate at 120VAC does not mean that they're compliant with FCC Part 15.
If you have specific examples of LED bulbs that are noisemakers, please complain to the FCC. It's an easy and cheap fix on the manufacturing front (an extra capacitor and/or an inductor), but that doesn't mean that the manufacturers are even aware of the problem.
Kid-proof tablet..
If you think I sound resentful, that is your own perception. I am stating the fact that there are numerous reasons for eye strain in work environments and this guy made no indication that he had positively identified the source of his eye strain to be his monitor. If you are trying to solve a problem, it makes sense to try to isolate the source of the problem.
How arrogant! The range of experiences posted by non- AC users here should have convinced you of the silliness of your post by now. Next time, be less sure of yourself.