Three Flashes or Below Threshold ensures that any content that flashes or flickers on the screen does so safely, reducing the risk of causing seizures or other physical reactions.
This is not the same as 2.3.2 Three Flashes, because it has some wiggle room built into it, but the thresholds are quite complex and involve size, brightness, and other factors. We will simply tell you not to do it, but you can check the further reading section if you need the details.
Who this impacts
- People with photosensitive epilepsy: Flashing content, especially at certain frequencies, can trigger seizures in people with photosensitive epilepsy.
- People with neurological disorders: Rapid flashes can also cause discomfort or confusion for users with other neurological conditions.
- Everyone: Even for users without medical conditions, flashing content can be visually overwhelming and distracting.
How to meet Three Flashes or Below Threshold
- Limit flashing content: Ensure that content doesn’t flash more than three times within a one-second period.
- Stay below the danger threshold: Make sure that any flashing content does not exceed the general flash and red flash thresholds to ensure user safety.
- Test with real content: Use tools to check for flash frequency in your media, especially in videos, animations, and other dynamic content.
Exceptions
In rare cases where flashing is necessary for the content, such as medical education videos about seizures, exceptions may apply. However, alternative content should be offered where possible, and users should be warned ahead of time.
Top tips
- Minimize or eliminate flashing: Don’t use flashing content. If you must use it, ensure it stays within safe frequency limits.
- Test flashing content: Use tools to analyze the flashing frequency and make sure it complies with the WCAG guidelines.
- Provide warnings for flashing: If flashing content is absolutely necessary, consider adding warnings or offering alternative versions for users who may be affected.