Facts about seizure conditions and making communication accessible
Some people with a range of conditions including epilepsy can have seizures as a result of strobing, flickering, or flashing effects.
This is sometimes called a photoepileptic seizure because it is caused by pulses of light interacting with the eye's light-receptive neurons and the body's central nervous system.
Accessible communication for people with seizure conditions
Most web content is harmless for people at risk of photoepileptic seizures. Even most animations, videos, moving text and Flash objects do not present any danger.
However, some developers use flashing or flickering lights and strobe-like effects. Obviously, they do this to have a particular impact and achieve a particular feel for the site. However, developers and those who commission websites should ensure that their content does not have strobing, flickering, or flashing effects.
Refer to Ofcom's guidelines
on flashing images which are designed to limit
incidences of seizures and consider testing any
broadcast material before it goes live.
Annoyed users will be distracted, which is an added problem for users with attention deficit disorders or some types of learning disability.
The size of the object can determine whether it will cause a photoepileptic seizure. Small flickering objects probably cause no harm (though they may still be annoying and distracting). The larger the object, the greater the chance of causing a seizure.
Even if the object does not cause a seizure, it may cause nausea or dizziness in some people. In some instances, an image does not even need to move to cause these effects. High contrast graphics with tight parallel lines can have similar effects, due to the optical illusion that parts of the image are in motion.
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