8.15 WCAG 2.1 Success Criterion 2.3.1 − Three Flashes or Below Threshold

Ensure all flashing items are dimmed, and cover only a small area of the screen or the flash rate is three times per second or less. Otherwise, this may cause problems for people who suffer from epilepsy.

Before Rectification

In this example, the traffic light image is flashing too fast, and is too bright and covers a large part of the screen. This content can cause seizures in people prone to this problem.

After Rectification

It is better to replace flashing content with static content, or ensure the object flashes in only a small portion of the screen or the flash rate is less than three times a second.

WCAG 2.1 Reference:

https://www.w3.org/WAI/WCAG21/Understanding/three-flashes-or-below-threshold