A guide
The standard is clearer than you might expect, and most content sits well inside it. Here is the limit, how to spot content that pushes at it, and what we measure in our own.
Updated 9 September 2026
The short answer
Photosensitive epilepsy is rare, rarely presents in the first year, and most baby sensory content sits well inside the accepted safety limits.
But "most" is not "all", and the category has no oversight, so it is worth knowing what the limit actually is and how to spot content that pushes at it.
If your baby has a diagnosed seizure disorder, or a first-degree relative with photosensitive epilepsy, this is a conversation for your paediatrician rather than an article.
The limit
The widely used standard, from WCAG 2.3.1 and published internationally as ISO/IEC 40500, is three flashes in any one-second period. It is worth being precise about what that is: a general accessibility guideline for web and broadcast content aimed at the whole population, derived largely from studies of children and adults with diagnosed photosensitive epilepsy. It is not infant-specific, and as far as we can find, no infant-specific flash standard exists. We use it because it is the most relevant published threshold, not because it was written with babies in mind. Broadcast practice measures it slightly differently: a transition counts when 80% or more of the screen changes brightness by 20% or more, and up to three such transitions per second are permitted.
Two things follow from that definition which surprise people.
A pattern that reverses — a checkerboard swapping black and white squares, for instance — often does not count as a flash, because the overall screen brightness barely changes. Half goes dark as the other half goes light.
Conversely, a video with no obvious "flashing" can still cross the line if it cuts rapidly between a mostly-black scene and a mostly-white one. Hard cuts are flashes if the average brightness swings far enough, fast enough.
Risk
Because the threshold is general rather than infant-specific, it is worth understanding what it is protecting against. Photosensitivity affects a small minority of people with epilepsy, and sensitivity is strongly frequency-dependent. Response rates are low at 3 Hz and peak much higher, in the region of 15 to 20 Hz — which is why the threshold sits where it does, with a wide margin below the range that actually provokes responses.
Photosensitive epilepsy also typically presents later in childhood and adolescence rather than infancy. That is reassuring, but it is not a reason for content aimed at babies to be careless.
In practice
You do not need equipment. Three signals are enough:
Watch it yourself, at normal brightness, in a dim room. If it feels busy or makes you blink, that is worth trusting.
Look for rapid scene changes between dark and light. A video that cuts every second or two between a black background and a white one is the pattern most likely to approach the limit.
Be sceptical of very fast-cut compilations. Long looping videos assembled from many short clips are the most common place this shows up, because nobody measured the joins.
And the ordinary advice still applies: a dim room rather than a dark one, screen brightness down, and reasonable viewing distance all reduce whatever risk exists.
Ours
We measure mean-frame relative luminance across every video in the catalogue at 30 frames per second, and count any change greater than 10% within a third of a second. That is deliberately stricter than the broadcast test, which uses a 20% change across 80% of the screen.
On that harsher test, the highest reading anywhere in our catalogue is 0.56 qualifying transitions per second, against a general-population threshold of three. Most of our videos come in under 0.15. The highest readings are all peekaboo videos, where a character hides and reappears — and even those sit more than five times under the limit.
We publish this because it is checkable, not because it is remarkable. The full specification and sources are here.
Being clear
Flash safety is a narrow technical question and a reassuring answer to it does not make screen time advisable for an infant. Paediatric guidance generally discourages screen media below roughly 18 to 24 months, and we think that is sound.
This article is about one specific risk, measured against one specific standard. It is not medical advice, and if you have any concern about seizures in your baby, speak to your paediatrician or health visitor.