This translation has not been editorially reviewed yet. The German version is authoritative. Deutsche Fassung
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Why is nothing on the side allowed to flash more than three times per second?
Flashing content can trigger a seizure in people with photosensitive epilepsy. Level A (2.3.1) prohibits flashes over three times per second, but leaves exceptions for small areas and low red contrast. Level AAA criterion 2.3.2 deletes the exceptions: nothing on the side flashes more than three times per second, no matter how small or pale.
What the Criterion Requires
No element on the page changes between light and dark or between contrasting colors more than three times per second: no animation, no video, no flashing icon, no advertising banner. Level A allows flashes if the area is small (below about 21,824 pixels at the usual distance) or the brightness change is small. Level AAA does not allow it. A video with stroboscope scene therefore needs an edited version or a lock warning before playing.
For whom this counts
About three in a hundred people with epilepsy respond to light stimuli; For them, a flashing video can trigger a seizure, with a risk of falling and injury. People with migraines or vestibular disorders also react to flickers with nausea and headache. Because a seizure cannot be reversed, the criterion is one of the few where a single violation can seriously harm a person.
This is how we deal with it
The measurement finds animations and videos on the page; The flash frequency of a video does not measure it. For videos, there are analysis tools (such as PEAT) that check a file for dangerous sequences. The criterion belongs to the category AAA in knowledge; At Level A, the service checks 2.3.1 for CSS animations and flashing elements.
Examples
Small flashing symbol
.live-punkt { width: 10px; animation: blink 0.2s infinite; }
/* auf Stufe A erlaubt, weil die Fläche klein ist */.live-punkt { width: 10px; animation: none; }
.live-punkt::after { content: "LIVE"; }At level AAA, there is no exception for small areas or low contrast: nothing flashes more than three times per second.
- Search for animated elements: flashing clues, loading displays, banners, GIF images, background videos.
- Set each frequency to a maximum of three changes per second or delete the animation.
- Check videos with a flash analysis tool before publishing them; Cut out stroboscope scenes.
- Respect the operating system setting “Reduce movement” and then turn off all animations.
