Web Development
Web Developer Guidelines
Visual Design Recommendations

Checkpoint 1.22 - Java

Flashing content is slower than 2 Hertz

WCAG 1.0 Priority 1

WCAG Guideline 7. Ensure user control of time-sensitive content changes.

A flickering or flashing screen may cause seizures in users with photosensitive epilepsy. Seizures can be 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).


Flashing content is slower than 2 Hertz


Ensure that any flashing or blinking components cycle at less than 2 Hertz or greater than 59 Hertz and avoid flashing which has a high level of contrast between the states.

As smaller areas are less likely to cause seizures, keep the area of the screen that is flashing to a minimum.

Checking Tool

Review all of the blinking elements in the application.

Review the simulated Flickering Images Demo available using the AIS toolbar on Internet Explorer: Tools > Simulations > Flickering Images Demo

Information Source

The original source of this information is located on the W3C web site  (www.w3.org/TR/WCAG10-TECHS/#tech-avoid-flicker)


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