Some people with photosensitive epilepsy can have a seizure triggered by displays that flicker, flash, or blink, particularly if the flash has a high intensity and is within certain frequency ranges.
There are two major organisations that have produced guidance on accessibility for people with disabilities, including guidelines on designing with regards to photosensitive epilepsy:
World Wide Web Consortium (W3C)
The W3C was created in October 1994 to lead the World Wide Web to its full potential by developing common protocols that promote its evolution and ensure its interoperability. Web Content Accessibility Guidelines 1.0 were adopted in 1999. In connection with photosensitive epilepsy, as part of ‘good practice’, designers should:
- allow users to control flickering, avoid causing the screen to flicker
- allow users to control blinking, avoid causing content to blink
- allow users to freeze moving content, avoid movement in pages
If the user is unable to control the flickering, blinking and moving (this includes stopping these effects from starting), then these effects should not be used.
The guidelines 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)."
United States Government
Section 508 of the US Rehabilitation Act requires that Federal agencies' (central government) electronic and information technology is accessible to people with disabilities. To this end, the US General Services Administration has produced standards to ensure that websites are accessible. Many US companies have adopted the Section 508 standards as good practice.
Section 508 would appear to be less stringent than the W3C's guidelines. There is one standard – §1194.22, paragraph j – which is is consistent with the first W3C's guideline (on the control of flickering), however, it would appear that none of the other W3C's guidelines have equivalents under the Section 508 standards.