Techniques for WCAG 2.0

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G19: Ensuring that no component of the content flashes more than three times in any 1-second period

Important Information about Techniques

See Understanding Techniques for WCAG Success Criteria for important information about the usage of these informative techniques and how they relate to the normative WCAG 2.0 success criteria. The Applicability section explains the scope of the technique, and the presence of techniques for a specific technology does not imply that the technology can be used in all situations to create content that meets WCAG 2.0.


Applies to any technology

This technique relates to:


The objective of this technique is to avoid flashing at rates that are known to cause seizures if the flashes are bright and large enough. Since some users may be using screen enlargers, this technique limits the flashing of any size content to no more than three flashes in any 1-second period.

Note 1: This technique is stricter than the Level A Success Criteria but is easier to test and can be used to meet the Level A Success Criteria because all failure thresholds in the Level A Success Criteria involve flashing 3.5 flashes or more within one second. Most content does not flash at all and even content that blinks does not blink this fast except on rare occasions. Therefore, in order to avoid having to carry out the more complex testing specified by the Success Criteria, one could follow this technique to ensure that content only flashes one, two, or at most three times in any 1-second period.

Note 2: Regarding 3.5 Flashes; if there are seven transitions from dark to light or light to dark, it would be 3.5 flashes, which is more than the allowed three flashes (six transitions).

Examples of 3.5 flashes or seven transitions:



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  1. Check that there are no more than three flashes during any 1-second period.

  2. If there are three flashes, check that the Light/Dark status at the end of the 1-second period is the same as at the start.

Expected Results

If this is a sufficient technique for a success criterion, failing this test procedure does not necessarily mean that the success criterion has not been satisfied in some other way, only that this technique has not been successfully implemented and can not be used to claim conformance.