Understanding Accessibility
by Vivienne Trulock
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Guideline 7. Ensure user control of time-sensitive content changes.
Checkpoint 7.1 - Until user agents allow users to control flickering, avoid causing the screen to flicker
Individuals suffering from epilepsy may suffer an attack if the screen flickers or mimics strobe light effects where the flicker rate is between 4 and 59 flashes per second. The peak rate occurs at 20 flashes per second.
How do I do it?
The easiest way to avoid this checkpoint is to not use animated gifs. If you are making your own animated gifs, set the delay time so that the flicker rate is outside the range of 4 to 59 flashes per second or Hertz (Hz). Hz = Delay Time in hundredths of a second / 50.
How do I check that it meets the WCAG criteria?
Pages can be checked for flickering using a flickering check tool. Those pages which have no flickering elements will pass. Flickering elements which are not in the critical range will be deemed to have passed. Flickering elements in the critical range or close to peak sensitivity will fail.
