Note: The creation of this article on testing Three Flashes or Below Threshold was human-based, with the assistance of artificial intelligence.
Explanation of the success criteria
WCAG 2.3.1 is a Level A conformance level Success Criterion. It ensures that web content does not contain anything that flashes more than three times in any one-second period, unless the flashes are below the general or red flash thresholds that could trigger seizures.
My historical example of a site that could fail this success criterion (warning: this example fails this success criteria and could trigger seizures), thankfully went through a redesign, losing the triggers that could cause seizures, but keeping with the holistic feel of the site.
Who does this benefit?
WCAG 2.3.1 Three Flashes or Below Threshold primarily benefits:
- People with photosensitive epilepsy, who can experience seizures triggered by flashing or strobing content.
- Individuals sensitive to flashing or strobing visuals, including those with certain neurological or vestibular conditions.
- Users with cognitive or attention-related challenges, as excessive flashing can be distracting or overwhelming.
Testing via Automated testing
Automated testing can quickly scan pages for obvious flashing elements and highlight sequences that exceed the three-flash or threshold limits, making it efficient for large sites, but it may miss context-specific flashes, subtle animations, or dynamically triggered content.
Testing via Artificial Intelligence (AI)
AI-based testing can improve on this by analyzing complex visual patterns, timing, and even contextual likelihood of flashes, offering deeper insights than standard automation, yet it can produce false positives or require significant configuration and oversight.
Testing via Manual Testing
Manual testing is the most reliable for catching nuanced issues, assessing user experience, and verifying real-world flash behavior, especially for dynamic or interactive content, but it is time-consuming, labor-intensive, and can vary depending on the tester’s skill or perception. Combining approaches often yields the most accurate and practical results.
Which approach is best?
No single approach for testing Three Flashes or Below Threshold is perfect. A hybrid approach leverages the strengths of automated, AI-based, and manual methods to ensure both efficiency and accuracy.
Start with automated testing to quickly scan the site for obvious flashing elements and flag content that exceeds the three-flash or threshold limits, covering large volumes of pages in minimal time. Next, use AI-based testing to analyze complex animations, dynamically generated content, and patterns that may not be obvious to standard automation, helping to identify subtle or context-sensitive flashing issues. Finally, conduct manual testing to validate results, observe real-world user interactions, and catch nuanced cases, such as conditional flashes, user-triggered animations, or content that AI may misinterpret.
This layered strategy ensures thorough coverage while optimizing resources and minimizing the risk of overlooking potentially harmful flashing content.
Related Resources
- Understanding Success Criterion 2.3.1 Three Flashes or Below Threshold
- A11y 101: 2.3.1 Three Flashes or Below Threshold
- Keeping the flashing area small enough
- Using a tool to ensure that content does not violate the general flash threshold or red flash threshold
- Trace Center Photosensitive Epilepsy Analysis Tool (PEAT)
- Information about Photosensitive Seizure Disorders
- Epilepsy Foundation – Photosensitivity and Seizures