Overview

Some people may be in spasm caused by a strobing, flickering or flashing. This type of spasm is sometimes called photosensitive epilepsy because it is caused by pulses of light (hence the prefix "photo") interacting with the light receptor cells in the eye and central nervous system of the body.

Most Web content is totally harmless to people with epilepsy are photosensitive. Even most of the animations, video, text and animated Flash objects are safe. However, some developers to take dramatic aspects created by flashing or flickering lights and strobe effects. Flash objects for science fiction, movie trailers horror movies and cheap banner ads are examples of misuse of these effects. Perhaps the creators of these effects think they are "cool", but they are also potentially dangerous. Developers should make every effort to ensure that their contents do not produce stroboscopic effects of blinks or flashes.

What are strobe effects, the flashes, the flashes?

Section 508 of the Rehabilitation Act prohibits US flickering effects with a frequency greater than 2 Hz and lower than 55 Hz Truly, this is an arbitrary designation. Most people do not realize a flicker at 55 Hz the other hand, virtually everyone is aware of a flashing arriving two times per second, and is probably bored without up to a photosensitive epileptic spasm. In addition, users are embarrassed distracted by the flashing, which goes against another principle of accessibility: help the user to focus on core content, which is particularly important for users with of attention disorders or with certain types of cognitive impairment.

The size of the object on the screen plays a role in whether it can cause photosensitive epileptic spasm. Small objects flashing not likely to cause problems (although they will probably always annoying and distracting). The larger the object, the more likely it is that causes a crisis.

Even if the object does not cause spasm, it may cause nausea or dizziness in some people. Neither of these two evils is not a health risk as can a real crisis, but have users who associate your website with a feeling of nausea is probably not the best design decision, at least in terms of user satisfaction and loyalty to your site.

In some cases, an image does not even need to move to cause these effects. Graphs with a High Contrast and tight parallel lines may have similar effects due to the optical illusion that parts of the image are moving.