2.3.1 - Flashes

Do not show anything that flashes more than three times a second.

Summary

A page must not contain content that flashes more than three times a second.

Requirements

  • Content does not flash more than three times a second.

Why?

  • Visual flicker, flashing and strobe lighting can affect anyone, but some users will be more susceptible than others.
  • Symptoms may include eyestrain, dizziness, fatigue, headaches, migraine, and nausea.
  • Users with medical conditions such as Ménière's or photosensitive epilepsy can be severely affected, experiencing vertigo, hearing loss and seizures.

A well-documented example of the effects of flicker is Pokémon Shock – this article is safe to view.

Official wording in the Web Content Accessibility Guidelines

2.3.1 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. (Level A)

See the W3C's detailed explanation of this guideline with techniques and examples.

Discuss on Twitter • View on GitHub • Main Sources