Pages that have flickering and flashing elements can cause several accessibility problems. A flickering or flashing screen may cause seizures in users with photosensitive epilepsy. Because of this, web developers should avoid creating pages that flicker at a rate that is likely to cause seizures. Seizures can be triggered by flickering or flashing in the 4 to 59 flashes per second (Hertz) range with peak sensitivity at 20 flashes per second. Some banner ads, designed to grab attention, flash or flicker at rates that may indeed induce seizures in those susceptible to them.

Also screen readers can be set to report any new information appearing on the screen. Blinking or flashing text is sometimes reported over and over, interrupting the users reading of the screen.

Example of Page Flicker