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Three Flashes:
Understanding SC 2.3.2

2.3.2 Three Flashes: [begin add] Web pages do [end add] [begin delete]Content does[end delete] not contain anything that flashes more than three times in any one second period. (Level AAA)

Intent of this Success Criterion

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The purpose of this success criterion is to further reduce the chance of seizures. Seizures cannot be completely eliminated since some people are so sensitive. However, by eliminating all 3-per-second flashing over any area of the screen, the chances of a person having a seizure are further reduced than when just meeting the measures ordinarily used today in standards internationally, as we do at Level A. [2327]

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The intent of this success criterion is to allow users to access the full content of a site without inducing seizures due to photosensitivity.

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Success Criterion 2.3.1 requires that flashing content be less than three flashes in any 1-second period unless it is smaller than 25% of a person's central vision for a typical screen. However, some users access Web content through screen enlargers. For these people, the area described in section 2.3.1 would (when magnified) be more than 25% of a persons central vision.

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This success criterion (2.3.2) eliminates all flashing components that flash more than three times in any 1-second period. In this fashion, magnification at any level would not yield content that would fail the general flash or red flash thresholds.

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Note: In some cases, what we refer to as "blinking" and what we refer to as "flashing" may overlap slightly. We are using different terms for the two because "blinking" causes a distraction problem which you can allow for a short time as long as it stops (or can be stopped) whereas "flashing" is a seizure trigger and cannot be allowed or it will cause a seizure. The seizure would occur faster than most users could turn it off. "Blink" therefore refers to slow repeating changes that would distract. "Flash" refers to changes that could cause a seizure if they were bright enough or persisted long enough. Blinking usually doesn’t occur at speeds of 3 per second or more so blink and flash do not overlap. However, blinking can occur faster than 3 per second so there could be an overlap. See Understanding Succes Criterion 2.2.2 for more information on blink. [2289]

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Specific Benefits of Success Criterion 2.3.2:

  • Individuals who have seizures when viewing flashing material will be able to view all of the material on a site without having a seizure and without having to miss the full experience of the content by being limited to text alternatives. This includes people with photosensitive epilepsy as well as other photosensitive seizure disorders.

Examples of Success Criterion 2.3.2

Related Resources

Resources are for information purposes only, no endorsement implied.

Techniques and Failures for Success Criterion 2.3.2 [Three Flashes]

Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this success criterion. The techniques listed only satisfy the success criterion if all of the WCAG 2.0 conformance requirements have been met.

Sufficient Techniques

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

Additional Techniques (Advisory)

Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.


The following are common mistakes that are considered failures of Success Criterion 2.3.2 by the WCAG Working Group.

(No failures currently documented)

Key Terms

Web page

[begin add]a non-embedded resource [begin delete]that is referenced by a URI[end delete] [begin add]obtained from a single URI using HTTP[end add] plus any other resources that are used in the rendering or intended to be rendered together with it by a user agent [end add] [begin delete]a resource that is referenced by a URI and is not embedded in another resource, plus any other resources that are used in the rendering or intended to be rendered together with it[end delete] [1948]

Note 1: Although any "other resources" would be rendered together with the primary resource, they would not necessarily be rendered simultaneously with each other.

Note 2: For the purposes of conformance with these guidelines, a resource must be "non-embedded" within the scope of conformance to be considered a Web page.

Example 1: A Web resource including all embedded images and media.

Example 2: A Web mail program built using Asynchronous JavaScript and XML (AJAX). The program lives entirely at, but includes an inbox, a contacts area and a calendar. Links or buttons are provided that cause the inbox, contacts, or calendar to display, but do not change the URL of the page as a whole.

Example 3: A customizable portal site, where users can choose content to display from a set of different content modules.

Example 4: When you enter "" in your browser, you enter a movie-like interactive shopping environment where you visually move about a store dragging products off of the shelves around you [begin add]and[end add] into a visual shopping cart in front of you. Clicking on a product causes it to be demonstrated with a specification sheet floating alongside.