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Photosensitive Epilepsy

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From: Hall, Kevin (K.M.)
Date: Aug 10, 2004 3:02PM






Photosensitive Epilepsy




Hi all, I'm just joining the group. I searched the discussion archive and found no mention of photosensitive epilepsy. I've been trying to track down some concrete guidelines and real examples of patterns that will cause problems and ones that are safe. However I keep finding guidelines like these from the W3CAG 2.0, found at http://www.w3.org/TR/2004/WD-WCAG20-20040730/#flicker:

Spatial Pattern Thresholds


Clearly discernible stripes consisting of more than five light-dark pairs in any orientation are not permitted when the stripes are stationary when the pattern occupies more than 40% of any 355 x 268 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 by 768 pixels.

Clearly discernible stripes consisting of more than five light-dark pairs in any orientation that change direction, oscillate, flash, or reverse in contrast are not permitted when the pattern occupies more than 25% of any 355 x 268 pixel rectangle anywhere on the displayed screen area when the content is viewed at 1024 by 768 pixels.


Clearly discernable stripes are stripes where the screen luminance of the darker bars in the pattern is below 160 cd.m -2 and differs from the lighter bars by 20 cd.m -2 or more (see notes 1 and 2 below).


The discussion of gamma and luminance is not actually that helpful and people appear reluctant to post images on websites discussing epilepsy that will cause seizures, which, though understandable as a precaution for those who might come across them accidentally, is making it difficult to make sense of the discussion of luminance differences. What exactly consitutes a light-dark pair. How can I check that? Could my alternating row colors in data tables cause seizures?

Does anyone have some concrete examples of patterns that will cause seizures and those that are safe? Perhaps some more understandable rules for what to avoid? Forgive my ignorance if the above directions from the W3C are obvious to you.

Thanks,

-Kevin