WCAG 2.3.1 — Three Flashes or Below Threshold

Who Is Affected

People with photosensitive epilepsy (affects 3-5% of those with epilepsy), users with vestibular disorders, people with migraine sensitivity, and users taking medications that increase photosensitivity.

What This Means

Content that flashes, blinks, or strobes more than three times in any one-second period can trigger seizures in susceptible individuals. This includes animated GIFs, auto-playing videos with rapid scene changes, flashing banner ads, JavaScript animations, and CSS animations with rapid color transitions.

Even content that flashes exactly three times per second is dangerous — the threshold is "three flashes or below," meaning content should flash no more than twice per second to be safe.

Fix: Content Editor

1. Identify flashing content on your pages:

   • Animated GIFs with rapid color changes
   • Auto-playing videos with strobe effects or rapid cuts
   • JavaScript slideshows with quick transitions
   • CSS animations that rapidly change brightness or color
   • Embedded ads or widgets with flashing elements

2. For each piece of flashing content:

   • Remove it entirely if it's not essential to your message
   • Replace with a static image that conveys the same information
   • Slow down the animation to flash no more than twice per second
   • Add user controls to pause, stop, or hide the animation

3. For video content:

   • Review videos for scenes with rapid flashing, strobe lights, or quick cuts between high-contrast scenes
   • Edit out problematic sequences or add a warning before the video
   • Ensure auto-play is disabled — users must choose to start the video

4. Test your fixes:

   • Use the Photosensitive Epilepsy Analysis Tool (PEAT) to analyze video content
   • Manually count flashes — if you can count more than 2 flashes in one second, it's too fast

Fix: CMS / Theme

If flashing content appears across multiple pages due to theme elements:

For Joomla:

1. Go to Extensions → Modules and review any carousel, slideshow, or banner modules
2. Access module settings and reduce transition speed or disable auto-advance
3. Check Extensions → Plugins for any animation or effect plugins that might create flashing

For WordPress:

1. Go to Appearance → Widgets and review any slideshow or banner widgets
2. Check active plugins for slider, carousel, or animation plugins
3. Access plugin settings and disable or slow down any rapid transitions
4. Review your theme's animation settings in Appearance → Customize

Standard Reference

WCAG 2.1 Success Criterion 2.3.1 — Three Flashes or Below Threshold, Level A

Web pages do not contain anything that flashes more than three times in any one second period, or the flash is below the general flash and red flash thresholds.

• W3C Understanding SC 2.3.1
• WCAG Technique G19 — No component flashes more than 3 times
• WCAG Technique G176 — Keeping flashing area small
• WCAG Failure F7 — CSS blinking content