Three Flashes or Below Threshold
Web pages do not contain anything that flashes more than three times in any one second period, or the flash is below the general flash and red flash thresholds.
In plain language
Nothing on a page should flash more than three times per second — flashing lights can trigger seizures in some people.
Why it matters
People with photosensitive epilepsy can have a seizure triggered by fast, bright flashing content, especially large flashing areas or flashes with a lot of red. This isn't just uncomfortable — it can be a serious medical risk.
In practice
Fails this criterion
A promotional video includes a strobe-light effect flashing 5 times per second across a large part of the screen.
Meets this criterion
The same effect is limited to flashing no more than 3 times per second, or is kept to a small enough area of the screen to stay under the safety threshold.
Test it yourself
Watch any animations, videos, or ads on the site. If anything flashes rapidly (more than 3 times per second) across a large area, this criterion is failing — this must be fixed, never just worked around with a warning.