§1194.22(j) Pages shall be designed to avoid causing the screen to flicker with a frequency greater than 2Hz and lower than 55 Hz.

Checkpoint
Does the page contain repeatedly flashing images?

Explanation
Animated .gif files and videos that flash the same image, or a rapid succession of similar images, can be considered repeated flashing images. Users with photosensitive epilepsy are subject to seizures triggered by such flickering or flashing effects, and even the average user can suffer headaches or dizziness from rapid flashing that can come from animation or video.

Guidelines
Simply put, developers shall not use repeatedly flashing images where the rate is 2Hz (Hertz) to 55Hz (Hertz) flashes per second.

Checkpoint
Does the page contain a strobe effect?

Explanation
Strobe effects can be described as abrupt changes from light to dark. The more common definition of a strobe effect is when those abrupt changes are repetitive. Users with photosensitive epilepsy are subject to seizures triggered by strobe effects, and even the average user can suffer headaches or dizziness from abrupt color changes.

NOTE: The naturally occurring 'flicker' caused when moving from one page to another is not considered a strobe effect, and therefore does not have to be addressed.

Guidelines
Developers shall not use strobe light effects - abrupt changes from light to dark - or use flashes in any color range at a rate of 2Hz (Hertz) to 55Hz (Hertz) flashes per second.

Checkpoint
Is the flicker rate between 2Hz (Hertz) and 55Hz (Hertz)?

Explanation
Users with photosensitive epilepsy are most vulnerable to flicker rates between 2Hz (Hertz) to 55Hz (Hertz) flashes per second range.

NOTE: The naturally occurring 'flicker' caused by the browser when moving from one page to another does not cause a flicker rate between 2Hz (Hertz) and 55Hz (Hertz), and therefore does not have to be addressed.

Guidelines
When in doubt about the flicker rate, developers should avoid incorporating any type of flickering mechanism.

Keep in mind that flicker is not the rolling line or similar effect of the 60Hz (Hertz) transmission frequency sometimes seen on older, weaker monitors.