Submitted by Alexis Wilke on Sun, 07/10/2011 - 14:27
Today I was visiting the American Cancer Society when I stumble upon a strange sentence... Now I'll have to think about means to inform Snap! users whenever they are creating a page that could be affected.
The sentence goes like this:
The figure to the right shows the accessibility of an handicapped person in a wheelchair.
Click on the picture to see the full figure from Section 508 paragraph 1194.41.
I understood the sentence, it means that there should be no animations running at the wrong speed on your website pages. 2 Hz pretty much means that nothing moves (static text and images.) 55 Hz is roughly the speed at which your eyes see,, if something goes at 55 Hz or more, then your eyes cannot see any jitter or flashing effects (i.e. flicker.)1
The sentence comes from Section 508, a set of regulations that you want to comply with so as to be able to tell your users that your website is accessible by visually, auditory or motor impaired people.
A certain number of people are susceptible to changing lights when at the wrong frequency (between 2 and 55 Hz). Computer monitors displaying an animation are often running between 12 and 30 Hz. Such animations can cause seizures in people who have photosensitive epilepsy2.
Especially bad are Flash or GIF animated ads. Many of those are at the wrong speed and can cause problems.
So... to comply with Section 508 frequency limits:
In general, the following are acceptable:
Complete Reference: Section 508.