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WCAG 2.3.1: Three Flashes, or Below Threshold


If you've been following along and you're still with us (hi there!), we're now moving onto Guideline 2.3, which goes over how to avoid designing content that may cause seizures or other physical reactions. In this post, we'll talk about flashes.

WCAG 2.3.1 asks that your site not contain any features that flash more than three times per second, as such features would negatively affect anyone who is prone to photosensitive seizures. If your site does include a feature that flashes more than three times per second, then it must be below certain general flash and red flash thresholds. We'll talk more about these thresholds and how to check your content against them in a bit.

What Is a Flash, Exactly?

It may seem like a dumb question, but if you've been following our posts in this series, then you may recall that we discussed "blinking" features previously, so it's worth taking a moment to distinguish between the two.

The terms "blinking" and "flashing", as WCAG uses them, can sometimes apply to the same content. Content should be referred to as "flashing" if

  • It can potentially induce seizure. "Blinking" applies only to content that could cause a distraction.
  • It is flashing more than three times per second. Blinking content rarely occurs at this rate. If it does occur faster than three times per second, then you would refer to the content as "flashing".

Flashing features can come from the display, the manner in which computers render an image, or by the content on the site. You, as the content author, only have control over the third item on that list. The design and speed of the display and computer can fix any flashing that comes as a result of the display or image rendering.

[Link: https://en.wikipedia.org/wiki/Lightning#/media/File:Staccoto_Lightning.jpg]

Examples of flashing content you may come across can include video or animation of strobe lights, lightning, or close-ups of rapid-fire explosions. Those affected by flashing content tend to be even more sensitive to red flashes than other colors.

A Handy Tool

I mentioned earlier in this post that if you do have content that flashes more than three times per second, then it must be below certain general and red flash thresholds. These thresholds take into account various elements that may render flashing content more or less dangerous for users prone to seizure. Color, size, and dimness of the flashes, for instance, can affect the risk factor of a seizure occurring.

Fortunately, there are a number of tools you can download that will help you analyze your site and make sure it passes muster. One such tool you can download for free comes from the University of Maryland's Trace Research and Development Center.