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3d films and photosensitive epilepsy

Photosensitive epilepsy affects up to 3% of people with epilepsy. Seizures for photosensitive people are triggered by certain rates of flickering images or light. For most people seeing a film at the cinema is unlikely to trigger seizures. As so many films are now also released in 3D, we asked photosensitive epilepsy expert Professor Graham Harding whether 3D films could trigger seizures for people who have photosensitive epilepsy.

Professor Harding says

Pair of 3D glasses

"There are relatively few cases of photosensitive seizures in cinemas. The frame rate of normal cinemas is 24 frames per second, which would produce noticeable flicker and so be a risk to photosensitive people. However, the intensity in the cinema is very low (about one hundredth of a television set).

"With ‘real 3D’ films, three images are projected, at a combined rate of 48 flashes per second. Because the projected images are polarised – that is, aimed at each separate eye – that is 24 flashes per second to each eye. If one assumes that the polarising reduces the light output by fifty percent there should be even less risk of a seizure trigger for people with photosensitive epilepsy.

"This means you are only getting half the intensity of a normal cinema, but equally everything else in the cinema has a similar reduction so the contrast remains the same. It appears that this is like wearing sunglasses in a normal cinema."