Flashing lights and seizure risk: expert consensus (Fisher 2005)

Flashes at about 3–65 Hz are hazardous, with 15–25 Hz the most provocative. Accessibility standards built on this consensus allow no more than 3 general flashes and no more than 3 red flashes in any 1-second window.

A plain-language summary from binaural's reading notes, edited by Jude Mc. Last updated 10 November 2026. Not medical advice.

The question: Which kinds of flashing light and visual patterns can provoke seizures in photosensitive people?

What it found

• The hazardous flash frequency band is about 3–65 Hz, most provocative at 15–25 Hz; about 96% of photosensitive patients respond in the 15–20 Hz band (Harding and Jeavons).
• Photosensitivity prevalence is about 0.3–3%; light-induced seizure incidence is about 1 in 10,000, and about 1 in 4,000 at ages 5–24.
• Saturated red flashing and high-contrast striped or oscillating patterns (about 1–8 cycles per degree) are separately provocative.
• The web accessibility guideline WCAG 2.3.1 puts this into practice: no more than 3 general flashes and no more than 3 red flashes in any 1-second window; the stricter 2.3.2 allows no flashing above 3 times per second at all.
• In Ricci 1998, doubling screen refresh from 50 to 100 Hz cut EEG activation about 15-fold.

Limits

• Immersive, full-field content such as virtual reality needs a stricter area rule than the 25%-of-screen threshold.
• The 2005 review has been updated by a 2026 consensus that explicitly addresses designers of interactive media.

Where this sits

More in the library on safety.

This is our plain-language reading of the paper. It is not medical advice, and one study rarely settles a question.