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Section 6. Flashing

Accessibility Score Sheet Questions

6.1    Is flashing/flickering content avoided?

Rationale

Pages that contain text or images that are flickering/flashing at a rate between 2 and 55 Hz can induce seizures in people with photosensitive epilepsy, particularly if the flash has a high intensity (i.e. dramatic differences in contrast). This includes flashing text, turning graphics on and off, or repeatedly changing between different images on the screen. Individuals with multiple disabilities may magnify the screen, even a small area flashing may cause a seizure.

Many people have trouble concentrating when something is moving or flickering in their field of vision, and individuals with cognitive disabilities may not be able to disengage with the flashing item.

Because violating this standard can distract many and pose a life threatening health risk to a few, we recommend avoiding all flickering/flashing content.

Note: The caret flash rate can be adjusted and is required for some assistive technology to work. It flashing is not considered a violation of this standard.

Test Approach

1. Visually inspect the application to see if any flashing occurs.

Development Techniques

  • Avoid using flashing or flickering content if at all possible.
  • If flashing is required:
    • Use elements that do not blink or flicker at rates between 2Hz and 55Hz. The rate of flashing can be a difficult feature to test; however, simply count “one thousand, two thousand” and if the object blinks faster than that, it is blinking too fast. You can also compare the flash rate with the caret blink rate. The caret blink rate can be adjusted through the keyboard options in the Control Panel. If the cursor blink rate is set to slow, it will flash 1.2 times per second. The flash rate will increase 100 milliseconds for each notch up to the maximum of 5 times per second. Query the setting by calling GetCaretBlinkTime.
    • Minimize the area flashing as much as possible as smaller areas are less likely to cause seizures.
    • Avoid flashing that has a high level of contrast between the states. Some individuals are more susceptible to high intensity flashing.
    • Provide a warning before the flashing or flickering content is shown.
    • Consider providing an option that enables users to slow down or disable screen flashing, however careful consideration should be given before implementing this feature.

Posted: Jan 07, 2016 12:41 PM
Last Updated: Jan 07, 2016 12:41 PM