10. Pages shall be designed to avoid causing the screen to flicker with a frequency greater than 2 Hz and lower than 55 Hz. (508:J. W3C: 7.1 Priority 1)
People with photosensitive epilepsy can have seizures 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).
Do not use the BLINK and MARQUEE elements.
If blinking content (e.g., a headline that appears and disappears at regular intervals) is used, provide a mechanism for stopping the blinking.
If you feel you must highlight some text by causing it to flash on and off, then use the CSS, 'text-decoration: blink' attribute. Using CSS will allow users to stop the effect by turning off style sheets or overriding the rule in a user style sheet.
Of course, we can't show you an example of an image or text blinking at 20 flashes per second or we could be accused of trying to bring on an seizure.
The point is: be careful when designing animated .gif images or other refreshing content.
