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Re: Revising 2.4, cont.

From: Matt May <mcmay@bestkungfu.com>
Date: Wed, 23 May 2001 14:42:27 -0700
Message-ID: <01b001c0e3d1$52bc0e20$6501a8c0@sttln1.wa.home.com>
To: "Adam Victor Reed" <areed2@calstatela.edu>, <w3c-wai-gl@w3.org>, "Anne Pemberton" <apembert@erols.com>
----- Original Message -----
From: "Anne Pemberton" <apembert@erols.com>
> >Visual display units (VDUs)
> >
> >Contrary to public belief, the use of professional VDUs rarely presents
> any risk to the person with epilepsy. However, the use of domestic
> televisions as computer displays is likely to present a greater risk.
> People using televisions as computer or computer games displays should
> at a distance of 2.5 metres or more.
> >
> Seems there may not be any relativity to these types of seizures with
> computer monitors unless they are TV's ...

The paragraph looks to be referring to the screen itself, not to the content
displayed on it. TV sets flicker just under 60Hz (60 interlaced half-screens
per second) in the US/Canada/Japan (NTSC), and 50Hz elsewhere (PAL/SECAM).
To see how this might cause epileptic seizures at under 2.5 meters, sit a
couple feet away and wave your hand in front of the screen. Interlaced
displays flicker like crazy. Today's displays are almost all non-interlaced,
but interlaced monitors were common as recently as 7 or 8 years ago, and
many are likely to remain in use elsewhere in the world and in schools and
libraries that can't update.

The seizures I cited were caused by the content being displayed. A flicker
like the one I cited could cause a seizure whether it's on a TV set, a
computer display, a strobe light or up in the sky.

Flicker also is distractive to people with ADD. Even if research shows that
no one is at risk for photic seizures, the ability to control flicker
remains a priority.

> I'd like to suggest that the note about flicker and seizures be removed
> from the guidelines until and unless any hard data on it can be found.

I'd like to suggest it be left in until there's hard data to disprove it. I
think there's evidence in this thread that shows it's still an issue.

Received on Wednesday, 23 May 2001 17:43:52 UTC

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