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  • #2124609

    Epilepsy and CRT/LCD screen flicker


    by shanghai sam ·

    This is a topic that has plagued me for some time. I as well as many others see a flicker that often causes a seizure so for many the use of a computer is not an option. Some also see this flicker watching tube, plasma televisions, not sure about projection yet. Still studying on that. Though front projection use LCD, it is not the same when projected. Rear projection uses guns and seems the least problem.
    Unfortunately cost is an issue as well for many of these people.
    Higher refresh rate can help many, not all.
    Change in resolution in both directions, claimed to have helped some.

    Monitors, both CRT (cathode ray tube) and LCD (liquid crystal diode).
    As the fall off in intensity (from monitor), is progressive, not linear, for a simple example if your distance from the monitor is one foot and the nominal intensity (logarithmic progression base -2), is 1/2x then if two feet away 1/4x, three feet 1/9x, four feet 1/16x, five feet 1/25x, six feet 1/36x.
    So sit further from monitor.
    A video card that really does refresh at frequency set at without working at it.
    Monitors that support higher refresh rates with reasonable resolution though available, again cost.
    Lower color contrasts. Remove white as the default background, gray helps.

    Yet the flicker is still seen on all sizes, brands and types of monitors.

    OS?s, 98,Millenium+server,NT server, ME, XP, Linux- seem to be the only ones being delt with at this time.

    I sit six feet from a 29? monitor, have a very good video card lots of ram fast machine, and this is the best I have seen so far. Though this is not realistic for most.

    Peripheral vision is more likely to catch the flicker for anyone. Looking off to the side of the monitor though paying attention to it still, many will see this flicker.

    Any ideas?

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    • #3450787

      Epilepsy and CRT/LCD screen flicker

      by richard_barsby ·

      In reply to Epilepsy and CRT/LCD screen flicker

      Hi just one thought although bigger monitors allow a higher refresh rate sitting at the normal distance from a pc monitor this would bring more of the picture into the Peripheral vision area where flicker is more easily seen !. Lcd monitors are flcker free as the picture is only updated as and when the image changes therefore only moving pictures should show flicker ie video clips etc.


    • #3450730

      Epilepsy and CRT/LCD screen flicker

      by shanghai sam ·

      In reply to Epilepsy and CRT/LCD screen flicker


      The following is an extract from a site I’ve found. No doubt you’ve seen it too.

      The full site is at…

      (remove spaces from the above URL)

      Facts and Hints
      Seizures can be triggered in many ways and not all of the listed hints may apply in each case. It is best to avoid particular situations known to trigger seizures.

      Photosensitive epilepsy is rare.
      Seek expert diagnosis. By assuming you are photosensitive you may place unnecessary constraints on your lifestyle.
      In most cases seizures can be controlled with regular medication.
      Cover one eye to reduce the effects of flashing or flickering light.
      Wear sunglasses to reduce glare.
      Use a TV remote control.
      Photosensitive seizures happen during not after the photic stimulation.
      Most computer monitors do not present a problem.
      Seizures triggered by video games are most likely to occur within 30 minutes of play.
      Keep 2.5m from the TV orvideo game screen and 30cm from a computer monitor.
      It is rare for seizures to be triggered by hand held screens or watching a film.
      Camera flashes rarely trigger seizures unless fired in rapid succession.

      In a different part of that same article, they also suggest using a screen filter to reduce the effects of flickering.

      Its good to research stuff like this. Gives us an appreciation of other’s problems. Thanks.


    • #3425931

      Epilepsy and CRT/LCD screen flicker

      by shanghai sam ·

      In reply to Epilepsy and CRT/LCD screen flicker

      Visually Evoked Potentials are highest at 10 Hz and harmonics there of.
      VEP is triggered by IPS (Intermittent Photo Stimulation).
      When you read these studies, you will also see that subharmonics are also triggered.
      Example: If the stimulation is at 30 Hz, you will see a strong 10 HZ signal in the brain currents, and it does not matter if you measure by VEP or EEG.
      This effect is noticable, and documented, up to 70 Hz.
      These studies would seem to indicate that you should stay away from refresh rates under 70 Hz, and use a rate not divisible by 10.
      Read the studies by:
      Berger 1923
      Christian 1982
      Sakramoto 1993
      Zschocke 1995
      Rau 2001

      Regards, Chris

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