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Ask Slashdot: Does LED Backlight PWM Drive You Crazy? 532

Posted by timothy
from the it's-how-they-send-messages dept.
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.
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Ask Slashdot: Does LED Backlight PWM Drive You Crazy?

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  • No (Score:0, Insightful)

    by Anonymous Coward on Thursday June 20, 2013 @01:42PM (#44062439)

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

  • Sigh (Score:4, Insightful)

    by ledow (319597) on Thursday June 20, 2013 @01:43PM (#44062453) Homepage

    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).

  • No (Score:4, Insightful)

    by DogDude (805747) on Thursday June 20, 2013 @01:46PM (#44062479) Homepage
    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.
  • by barc0001 (173002) on Thursday June 20, 2013 @01:48PM (#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?

  • by DrGamez (1134281) on Thursday June 20, 2013 @01:54PM (#44062597)

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

  • by Belial6 (794905) on Thursday June 20, 2013 @02:10PM (#44062825)
    Waa I heard someone make a complaint that doesn't affect most people in third world countries, someone call the waambulance.
  • by gweihir (88907) on Thursday June 20, 2013 @02:11PM (#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.

  • by gweihir (88907) on Thursday June 20, 2013 @02:13PM (#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.

  • by techsimian (2555762) on Thursday June 20, 2013 @02:19PM (#44062975)

    The cycle rate for triggering seizures isn't typically that high. Most LED backlights cycle at 120hz (they should be driven ). Older LCD flatscreens had crappy tubes and had a very visible flicker.

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

    When functioning correctly, mains-powered fluorescent lighting has a flicker rate sufficiently high (twice the mains frequency, typically 100 Hz or 120 Hz) to reduce the occurrence of problems. However, a faulty fluorescent lamp can flicker at a much lower rate and trigger seizures.[4] Newer high-efficiency compact fluorescent lamps (CFL) with electronic ballast circuits operate at much higher frequencies (10–20 kHz) not normally perceivable by the human eye, though defective lights can still cause problems.

  • Re:Sigh (Score:5, Insightful)

    by DutchUncle (826473) on Thursday June 20, 2013 @02:36PM (#44063239)
    No. It's not necessarily just one person. Like allergies and other chemical sensitivities, each person who has a problem thinks they're weird, because nobody else seems to have the problem; but just like ANY OTHER aspect of humanity there is a wide range of reactions.

    I can see car brake LEDs flicker; my wife can't. Doesn't mean my eyes are better, or worse, just different. And that the car light systems could probably work better.

    Maybe it's not a tiny minority, and maybe it's not enough to make people ill. Maybe a tenth or a quarter of the world feels a little less well than they might all the time, but it's "just" a few percent so not enough to notice and each person thinks they just need more sleep. Or maybe a tenth or a quarter of the world is "just" a few IQ points lower than they might have been.
  • by PhotoJim (813785) <jim@@@photojim...ca> on Thursday June 20, 2013 @03:35PM (#44063937) Homepage

    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.

APL is a write-only language. I can write programs in APL, but I can't read any of them. -- Roy Keir

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