Web content accessibility guidelines

Flickering and Photosensitive Epilepsy

Legend:

Symbol	Meaning
	Single frame GIF image: null Flicker Rate
	Flicker Rate is not in the critical range
	Flicker Rate is in the critical range
	Flicker Rate is close to peak sensitivity
	Test error

WCAG 1.0
7.1 Until user agents allow users to control flickering, avoid causing the screen to flicker. [Priority 1]
Note. 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).

Section 508 - § 1194.22 Web-based intranet and internet information and applications
(j) Pages shall be designed to avoid causing the screen to flicker with a frequency greater than 2 Hz and lower than 55 Hz.

Requirement n. 5 , Published on www.pubbliaccesso.it
Terms: Avoid flickering or moving objects or text with an intermittent frequency could cause photosensitive epileptic seizures or disturb concentration, or could cause the assistive technology used to malfunction. If informative requirements require these objects or text to be used, warn the user of the possible risk before presenting them and provide means allowing these elements to be avoided.
WCAG 1.0 references: 7.1, 7.2, 7.3
Sec. 508 references: 1194.22 (j)
Comments: This requirement refers to the problems about using moving objects (textual or not). Three kinds of problems have been found: photosensitive epilepsy: in this case pages must be designed to avoid causing the screen to flicker with a frequency greater than 2 Hz and lower than 55 Hz (see Section 508)

Author: Renzo Giust  Translated by: Roberto Castaldo