Section 508, 1194.22(j)

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“Pages shall be designed to avoid causing the screen to flicker with a frequency greater than 2 Hertz and lower than 55 Hertz.”

WCAG 1.0 Checkpoint: 7.1


In other words, avoid flicker at frequencies that can trigger seizures in some people by not using the <blink> tag (now deprecated) and by avoiding creating items that blink on and off.

A flickering or flashing screen may cause seizures in users with photosensitive epilepsy and content developers should thus avoid causing the screen to flicker. Seizures can be triggered by flickering or flashing in the 4 to 59 flashes per second (Hertz) range with a peak sensitivity at 20 flashes per second as well as quick changes from dark to light (like strobe lights).


Core Techniques for Web Content Accessibility Guidelines 1.0: