Beta

Slashdot: News for Nerds

×

Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

Ask Slashdot: Does LED Backlight PWM Drive You Crazy?

timothy posted about a year ago | from the it's-how-they-send-messages dept.

Displays 532

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.

cancel ×

532 comments

first world problems (-1, Troll)

Anonymous Coward | about a year ago | (#44062413)

Waa my computer is too flickery, someone call the waambulance.

Re:first world problems (4, Interesting)

Urban Nightmare (147344) | about a year ago | (#44062451)

Might be a first world problem but that doesn't make any less real.

It will never change unless someone starts the conversation.

Re:first world problems (3, Interesting)

trum4n (982031) | about a year ago | (#44062839)

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.

Re:first world problems (0)

Anonymous Coward | about a year ago | (#44062657)

He probably also has to walk 15 feet to grab a new Cheetos bag.

Re:first world problems (2)

The Grim Reefer (1162755) | about a year ago | (#44062717)

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.

Seizure disorder (2)

tepples (727027) | about a year ago | (#44062765)

Waa my computer is too flickery, someone call the waambulance.

For people with photosensitive epilepsy, it might more more like "someone call the ambulance."

first world problems: Part II - The Irony (2, Insightful)

Belial6 (794905) | about a year ago | (#44062825)

Waa I heard someone make a complaint that doesn't affect most people in third world countries, someone call the waambulance.

Re:first world problems (4, Insightful)

gweihir (88907) | about a year ago | (#44062855)

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.

Re:first world problems (0)

Anonymous Coward | about a year ago | (#44062893)

Yeah about as serious as running out of ding dongs.

Whiny little bitch (0)

Anonymous Coward | about a year ago | (#44062419)

Would you rather have some 300 pound CRT monitor literally frying your eyeballs out of the back of your skull? Take and aspirin and get back to work, hipster-slacker-dweeb.

Re:Whiny little bitch (1)

Anonymous Coward | about a year ago | (#44062475)

I think you literally do not understand what the word "literally" means.

Re:Whiny little bitch (1)

Anonymous Coward | about a year ago | (#44062545)

I think you literally do not understand that some words are used in a figurative sense.

Re:Whiny little bitch (0)

Anonymous Coward | about a year ago | (#44062589)

literally /litrl/
Adverb

1. In a literal manner or sense; exactly: "the driver took it literally when asked to go straight over the traffic circle".
2. Used to acknowledge that something is not literally true but is used for emphasis or to express strong feeling.

Re:Whiny little bitch (1)

ttucker (2884057) | about a year ago | (#44062687)

I think you literally do not understand what the word "literally" means.

The difference between an xray tube and CRT tube is disturbingly subtle.

Re:Whiny little bitch (2)

Kozar_The_Malignant (738483) | about a year ago | (#44062797)

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.

Re:Whiny little bitch (2)

mark_reh (2015546) | about a year ago | (#44062859)

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.

Re:Whiny little bitch (1, Insightful)

DrGamez (1134281) | about a year ago | (#44062597)

If you wanted to use the phrase "literally" to mean "figuratively", couldn't you have just said "figuratively"?

Re:Whiny little bitch (-1)

Xtifr (1323) | about a year ago | (#44062697)

Why should he deliberately avoid a common, standard, and centuries-old (and found in every dictionary) use of a word just to satisfy misguided peevers who don't even know their own language? If you want a word that lacks the inherent ambiguity of "literally" (and ambiguity is found in the majority of common words in English), then use "actually".

Re:Whiny little bitch (0)

Anonymous Coward | about a year ago | (#44062791)

there is literally no ambiguity about the meaning of the word literally...

Re:Whiny little bitch (4, Insightful)

gweihir (88907) | about a year ago | (#44062877)

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.

Bitch, please (4, Funny)

Anonymous Coward | about a year ago | (#44062425)

Your comment gave me a headache. Also, are you allergic to Wi-FI?

Eye strain from LED backlit displays? (0)

Anonymous Coward | about a year ago | (#44062437)

Gimme a break. Whats next, your neighbours WiFi is making you sick?

No (0, Insightful)

Anonymous Coward | about a year ago | (#44062439)

http://en.wikipedia.org/wiki/Betteridge's_law_of_headlines

Sigh (4, Insightful)

ledow (319597) | about a year ago | (#44062453)

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).

Re:Sigh (2)

robthebloke (1308483) | about a year ago | (#44062637)

Yeah, sounds like he's having an acid flashback or something......

Re:Sigh (2, Interesting)

thule (9041) | about a year ago | (#44062665)

I think it is likely placebo. This is the first I've ever heard that people complain about LED lights. On the other hand I *still* hear people complain about fluorescent lights despite the fact that it is pretty rare to find ones driven by magnetic ballasts anymore.

Re:Sigh (4, Interesting)

Andy Dodd (701) | about a year ago | (#44062763)

I'm positive it's placebo here.

LED PWM frequencies are FAR higher than the old CRT refresh rates.

Also, while the OP talks about phosphor persistence, remember, the duty cycle of CRTs was VERY short. A pixel would only be "energized" for a tiny fraction of each display cycle. Even with phosphor persistence, I would not be surprised if even at very low brightness levels, PWMed LED backlights are still at a higher duty cycle than CRTs.

I have a friend who is extremely photosensitive - the flicker of fluorescent lights without high frequency ballasts make him begin feeling sick almost immediately, and before he was on seizure medications, would cause seizures. To use a PC monitor, he had to always have ultra-high-refresh rate CRTs - until LCDs became common. He has NEVER had ANY issues with any LCD monitor, regardless of whether the backlight was LED or CCFL. They have been a godsend for him.

how about DC backlight? (1)

swschrad (312009) | about a year ago | (#44062711)

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.

Re:Sigh (0)

Anonymous Coward | about a year ago | (#44062751)

"More expensive" ?
Seriously: upping the frequency outside the visual range should come at an increase of 0.01$
The biggest cost would be development of the higher frequencies, like the rest of the entire screen, capable of driving 1920x1060x60hz running at 1.65GHZ ...

MOD PARENT DOWN (0)

Anonymous Coward | about a year ago | (#44062829)

Seriously, just look up the numerous studies that have been done on this. This flicker is *extremely* annoying to a lot of people. Ever seen the LED tail lights on some Cadillacs that look like red strobe lights? C'mon, people!

Re:Sigh (0)

Blaskowicz (634489) | about a year ago | (#44062847)

Air conditioning makes me uneasy. It's like being in a fridge. Don't blow cold canned air in my face please, and don't make me experience 10C transitions when I get out or in. I'm in a rich western european country where A/C is uncommon in homes, and spent my childhood in cars without A/C, we were fine.

Certain high-end displays flicker on purpose (3, Informative)

Anonymous Coward | about a year ago | (#44062455)

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.

Re:Certain high-end displays flicker on purpose (1)

Blaskowicz (634489) | about a year ago | (#44062875)

Max brightness will burn your eyes out of sheer brightness. I've prefered CRT monitors as long as they are set to 85 or 100Hz to overbright LCD ones.

I'm not a pussy (0)

Anonymous Coward | about a year ago | (#44062457)

So I never had problems with either type of monitor.

Yeah (1)

zoomshorts (137587) | about a year ago | (#44062459)

You live with what we have, NOT whine about your own deficiencies... I am partially deaf. Have you ever seen me to whine about that?

CRT whine (0)

Anonymous Coward | about a year ago | (#44062473)

Well, you can at minimum reduce the CRT whine by casting the deflection coils in resin. Clumsy, but it works.

No (3, Insightful)

DogDude (805747) | about a year ago | (#44062479)

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.

Re:No (0, Flamebait)

DrGamez (1134281) | about a year ago | (#44062557)

These same people also will complain about "wifi sickness". Everyone has to be unique in some special way~

Re: No (0)

Anonymous Coward | about a year ago | (#44062835)

Well,
Some time ago with a coworker we were doing the setup for a point to point 5 GHz 802.11a wireless link, meant for bridging 1.5km distant endpoints.
While trying quickly the couple of AP in the lab, before installing them on the roof, well both me and my coworker got instant background headache while it was turned on (the units were 10 meters apart).
Maybe a coincidence?

Re:No (3, Interesting)

gnasher719 (869701) | about a year ago | (#44062559)

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.

Re:No (1)

SJHillman (1966756) | about a year ago | (#44062573)

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.

Re: Careful, strawman (0)

Anonymous Coward | about a year ago | (#44062837)

By your own admission, she said "at least you don't have horrible fluorescent lights."

In that context, it is unclear if she believes all fluorescent lights are horrible, or if she's referring to the subset of fluorescent lights that she believes are horrible. I choose to believe that you're beating a strawman by ignoring the fact that she was probably referring to the tube-type fluorescents with traditional / old-style ballast that NOBODY likes because they flicker at 1-2Hz and hum like they're singing you the song of their people.

Re:No (1, Informative)

DRJlaw (946416) | about a year ago | (#44062849)

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.

No, he's not. That whining noise is well known, objectively measurable, and explainable by actual physics.

Unless IBM was imagining things. [ip.com] . Or you deny the existence of eddy currents [raftabtronics.com] 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.

no, they don't(and a fix for you) (-1, Flamebait)

gl4ss (559668) | about a year ago | (#44062501)

perhaps you should buy some nasal clearing spray. it's summer and the pollen makes my eyes water and my breathing harder and that gives a headache.

also, is this an advert for prad?

another also, this is the first time I heard anyone bitch about this except people using cameras where it's visible. in fact I've bumped into many people who thought the usual way was to vary the voltage...

ALSO TURN THE FUCKING BRIGHTNESS TO MAXIMUM and your problem is solved.

Re:no, they don't(and a fix for you) (1)

jeffmeden (135043) | about a year ago | (#44062583)

also, is this an advert for prad?

I hope not, dass vor Ort saugt wie ein östlich Deutsch im Urlaub.

Flickering (0)

Anonymous Coward | about a year ago | (#44062511)

I've not noticed it in LCD's yet...but it could easily be I've not run across it yet. Is this just something newer LCD monitors are starting to do?

Back in the CRT days, a 60Hz refresh rate would drive me nuts. A 54Hz refresh rate on a problematic computer once actually gave me a headache. 72Hz was passable, and 75Hz the minimum at which I no longer noticed the flicker. 85Hz was even better. I remember seeing a Viewsonic monitor of some sort once that would handle 120Hz refresh rate at 640x480...and it looked amazing. What I always found interesting was how many people didn't notice the flicker at 60Hz at all...they just couldn't comprehend what I was talking about. I guess biologically, we are all a little different in that regard.

Re:Flickering (1)

SJHillman (1966756) | about a year ago | (#44062713)

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.

Is it only the monitor? (5, Insightful)

barc0001 (173002) | about a year ago | (#44062519)

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?

Re:Is it only the monitor? (1)

Anonymous Coward | about a year ago | (#44062621)

No fluorescent bulbs refresh at 60Hz. The ballast on most fluorescent bulbs tends to run in the 10 to 40kHz range. The only bulbs that refresh at line frequency are incandescent, but the resistive load of the filaments tends to level that flicker out a bit. But lets not let facts get involved with a good story.

Re:Is it only the monitor? (5, Informative)

ZorinLynx (31751) | about a year ago | (#44062775)

NEWER ballasts run in the 10-40kHz range.

Older fixtures still use magnetic ballasts. No solid state switching circuitry. Big, heavy, tar-filled ballsts that hum and drive the lamps at a good ol' 60Hz.

Sure, they last 10-15 years or so, and the drop-in replacements can be solid-state... But the magnetic ballasts are pervasive, manufactured by the millions, and are still sitting new-in-box in supply closets all over the world.

Re:Is it only the monitor? (1)

ttucker (2884057) | about a year ago | (#44062789)

No fluorescent bulbs refresh at 60Hz.

Contemporary fluorescent ballasts were just high voltage transformers running at AC line frequency. All of this fancy high frequency PWM stuff is very very new.

Re:Is it only the monitor? (1)

jeffmeden (135043) | about a year ago | (#44062805)

No fluorescent bulbs refresh at 60Hz. The ballast on most fluorescent bulbs tends to run in the 10 to 40kHz range. The only bulbs that refresh at line frequency are incandescent, but the resistive load of the filaments tends to level that flicker out a bit. But lets not let facts get involved with a good story.

Not to mention, 60hz AC has two peaks per cycle, one positive and one negative. So a bulb (incandescent or old fluorescent non-electronic ballasts which are still in use in a lot of buildings) using this as a power source directly (and not cutting off half of the wave for some reason) will flash twice per cycle, leading to 120hz operation.

Re:Is it only the monitor? (1)

Andy Dodd (701) | about a year ago | (#44062863)

Wrong. Nearly all tube-style fluorescents refresh at 60 (or 120 - one per half cycle) Hz.

High frequency electronic ballasts are RARE for tube-style fluorescents. CFLs are a different story - nearly all of these have high frequency electronic ballasts these days - but the "tube" style fixtures found in offices rarely have high frequency ballasts and use passive reactive ballasts instead.

Re: Is it only the monitor? (0)

Anonymous Coward | about a year ago | (#44062873)

No, dumbass, actually lots of fluorescents, especially in industrial settings, use magnetic ballasts such that they flicker at line frequency. (Well, at double mains frequency, but same goes for incandescents, so I hope you're not nitpicking on that basis.)

Re:Is it only the monitor? (1)

fuzzyfuzzyfungus (1223518) | about a year ago | (#44062755)

Ditching the old-school iron ballasts might not be a bad idea, either. They are seriously inefficient, and suffer from hum and flicker. Contemporary electronic ballasts perform considerably better.

Re:Is it only the monitor? (1)

WillgasM (1646719) | about a year ago | (#44062865)

I rarely turn the lights on. Unless there's a storm rolling through, I get plenty of glow through the closed window blinds. OSHA seems to think offices need to be saturated, but I can't stand florescents. Between the hum, flicker, and overall brightness, they drive me crazy. Employers often find it strange, but I think they get used to the idea of the IT guy in his dark cave. I even convinced my last boss to give it a try, and we just quit turning on the lights at all. Saves energy, reduces noise (both sonic and EMI), and keeps my eyes happy.

No (1)

MysteriousPreacher (702266) | about a year ago | (#44062521)

No. Used plenty of LED displays without issues.

THE NOISE (1)

DrGamez (1134281) | about a year ago | (#44062529)

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.

Re:THE NOISE (1)

ericloewe (2129490) | about a year ago | (#44062551)

How much time do you spend next to CRTs? And why?

Re:THE NOISE (1)

DrGamez (1134281) | about a year ago | (#44062633)

I guess it's not a lot thankfully, but now they have become rare enough that when I'm near one it's jarringly loud. To think my entire CRT-enjoying childhood I used to enjoy "knowing" when a CRT was turned on in a room.

I still won't miss it when it's gone!

Re:THE NOISE (1)

NixieBunny (859050) | about a year ago | (#44062577)

I can't hear the whine of a CRT any more, because they no longer exist in any room that I spend time in.

Re:THE NOISE (1)

DrGamez (1134281) | about a year ago | (#44062661)

But what about that one CRT you keep around for the pre-hd consoles?

Re:THE NOISE (0)

Anonymous Coward | about a year ago | (#44062785)

You don't have sdlmess installed yet?

Re:THE NOISE (0)

Anonymous Coward | about a year ago | (#44062821)

I do the sensible thing and own a top of the line 60" plasma. Resolution of an LCD (though no 4k yet, and maybe never) without the ugly jagged look. Brightness and response rates that make even the best LCDs weep.

good post (-1)

Anonymous Coward | about a year ago | (#44062553)

http://www.india4movie.com/

nope (1)

WillgasM (1646719) | about a year ago | (#44062563)

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.

No problems here (1)

mwn3d (2750695) | about a year ago | (#44062575)

I recently switched to an LED monitor. It can only refresh at 60 Hz (or 59Hz but who does that?). I haven't noticed any flickering or had any headaches. I have noticed less power consumption and less heat coming from my display so I think you're just gonna have to deal with it. The benefits of LED displays will outweigh stuff like this forever. You won't be changing the industry.

fluorescent lighting (1)

thule (9041) | about a year ago | (#44062587)

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.

Re:fluorescent lighting (1)

ttucker (2884057) | about a year ago | (#44062807)

People can see 40,000Hz on a properly working tube bulb?

This is about the frequency range that LED PWM drivers operate at.

No problem (2)

Zontar_Thing_From_Ve (949321) | about a year ago | (#44062591)

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.

Car Braklights!!! (2)

bradgoodman (964302) | about a year ago | (#44062593)

YESSS!!!!!!

I thought I was the only one - but perhaps I still am - but car LED brakelights have been driving me ***CRAZY** for years!!!!

Re:Car Braklights!!! (1)

Sponge Bath (413667) | about a year ago | (#44062803)

...car LED brakelights have been driving me ***CRAZY** for years!!!!

I see what you did there, and it gave me a headache.

Re:Car Braklights!!! (0)

Anonymous Coward | about a year ago | (#44062811)

You're definitely not alone. When I first read the title I immediately thought the same thing, seems to especially be a problem with the older Cadillacs. They have been getting better over the last few years however, maybe using a higher modulation rate so it's not quite as irritating.
I have the same problem with dimmed LED holiday lights.

Re:Car Braklights!!! (1)

Carnivore (103106) | about a year ago | (#44062883)

Nah, the taillights bug the shit out of me, too. I have no idea why they don't just increase the pulse frequency.

Temporal Dithering is Worse (0)

Anonymous Coward | about a year ago | (#44062595)

It maked your screen flicker as well, no matter how fast your backlight is flickering.

It's the saccades (3, Interesting)

Anonymous Coward | about a year ago | (#44062603)

Your eyes are always moving as well, these movements are called "saccades". I think that there is a "beat frequency" between your saccades and the PWM drive that probably triggers headaches. I wonder if it's possible to change the PWM frequency of the chipset just to experiment?

http://en.wikipedia.org/wiki/Saccades [wikipedia.org]

Nice troll... (3, Interesting)

Elledan (582730) | about a year ago | (#44062613)

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? :)

Re:Nice troll... (2)

h4rr4r (612664) | about a year ago | (#44062767)

The average CRT was crap. It flickered and whined like hell. The geometry on most of them was a total joke. Often the image bounced around too.

I have a very nice one I still use sometimes that does higher res than any LCD you can buy and uses a shadow mask. This cost multiples of the average POS crt.

No, it's not just you (1)

dennison_uy (313760) | about a year ago | (#44062645)

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.

Hard to say... (1)

Red_Chaos1 (95148) | about a year ago | (#44062647)

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.

Doesn't seem likely (1)

ericloewe (2129490) | about a year ago | (#44062659)

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.

No, but you may be on the autism spectrum (0)

Anonymous Coward | about a year ago | (#44062663)

I've found that neurotypical people tend not to be bothered by things like fluorescent lights, CRTs and LEDs/LCDs that use PWM. However, I myself can easily notice 60Hz flicker in fluorescent lights and CRTs that aren't running at a 75Hz+ refresh. LEDs/LCDs don't bother me, but I can see how someone with greater photosensitivity than I could find PWM'd LEDs/LCDs to be extremely annoying.

I highly suggest reading up on the visual effects that often happen to people on the autism spectrum. The UC Davis MIND Institute, for example, uses custom fluorescent fixtures that run at 300Hz instead of the standard 60Hz line frequency in order to reduce or eliminate the horrible flickering that photosensitive people notice. Temple Grandin has a really great talk, "My Experience with Autism", where she goes over the symptoms and root causes of certain symptoms, you can look it up on YouTube.

Photosensitivity isn't coupled hand-in-hand with autism, granted, but if you're working in a technical field already and you have photosensitivity, you might consider reading up on it.

Can you say psychosomatic? (0)

h4rr4r (612664) | about a year ago | (#44062667)

This is about as real as wifi giving people headaches.

Psychosomatic (1)

QuietLagoon (813062) | about a year ago | (#44062671)

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.

Single data point (1)

sjbe (173966) | about a year ago | (#44062691)

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.

Ah, for the old days (0)

Anonymous Coward | about a year ago | (#44062701)

I'd give anything to be able to go back to the easy-eyes days of big CRTs. You could set the resolution to anything you wanted. With a really good one (not those cheap noisy ones), and a good video card, it was like gazing at a calm blue sea.

But it's not going to happen, and I don't miss the heat.

What kind of display are you using? (1)

fuzzyfuzzyfungus (1223518) | about a year ago | (#44062703)

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?

Re:What kind of display are you using? (2)

Spy Handler (822350) | about a year ago | (#44062777)

He's probably using a El Cheapo monitor with a brand name like AOC or something. And it's probably defective.

I've never heard of anyone being bothered by LED flickering. I would suggest that he buy a quality brand like Samsung or LG so that he can be sure he as a good working unit. His current one has something wrong with it.

Re:What kind of display are you using? (2)

TeknoHog (164938) | about a year ago | (#44062823)

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').

For me it's the blue LEDs that drive me crazy, so perhaps the OP has a problem with the spectrum rather than flicker.

OLED (1)

Twinbee (767046) | about a year ago | (#44062721)

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.

Complainer (0)

Anonymous Coward | about a year ago | (#44062723)

I bet you complain about more than just monitors. I'm sure your friends and friend's wives just love to have you over as company.

what the heck? (1)

slashmydots (2189826) | about a year ago | (#44062741)

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.

Re:what the heck? (1)

h4rr4r (612664) | about a year ago | (#44062809)

There is another cause, white LEDS do not turn on and off very quickly. This is because they are really UV LEDs with phosphor painted on them.

Hunderds of Hertz? (0)

Anonymous Coward | about a year ago | (#44062759)

I would be surprised if frequencies of two or three hundred Hertz cause a problem in anyone. I have noticed that sometimes my MacBook Air has started to flicker at a visible rate when first used, but quickly settles down. The samples on PRAD are too quick to show flicker at a problematic rate. The most problematic rate is around 6-10 Hz, but varies wildly between people.

It appears similar technology is being introduced for office lighting, with disappointing results.

PWM Taillights (0)

Anonymous Coward | about a year ago | (#44062771)

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.

It does happen (3, Interesting)

GreenEnvy22 (1046790) | about a year ago | (#44062773)

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.

Refresh rates and backlight PWM are unrelated (1)

updatelee (244571) | about a year ago | (#44062779)

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

"watering eyes and headache" (1)

macraig (621737) | about a year ago | (#44062799)

Hey, jones_supa: It's not yer monitor, stoopid, it's yer cellphone... stop holding it next to yer head!

Re:"watering eyes and headache" (1)

Graydyn Young (2835695) | about a year ago | (#44062861)

Or it could be the wi-fi!

Go see an expert, you dope (5, Interesting)

wcrowe (94389) | about a year ago | (#44062881)

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.

Load More Comments
Slashdot Account

Need an Account?

Forgot your password?

Don't worry, we never post anything without your permission.

Submission Text Formatting Tips

We support a small subset of HTML, namely these tags:

  • b
  • i
  • p
  • br
  • a
  • ol
  • ul
  • li
  • dl
  • dt
  • dd
  • em
  • strong
  • tt
  • blockquote
  • div
  • quote
  • ecode

"ecode" can be used for code snippets, for example:

<ecode>    while(1) { do_something(); } </ecode>
Create a Slashdot Account

Loading...