On 4 June 2007, the organisers of the London 2012 Olympics unveiled the new logo for the Games. An associated short promotional film showed images of sport in London with moving, flickering, brightly-coloured patterns throughout, culminating with footage of a diver plunging into a pool of animated ripples. The release of this film was quickly followed by reports that it had triggered seizures in some people with epilepsy (see the statement released by Epilepsy Action) and the film was withdrawn.

Photosensitive epilepsy
Photosensitive epilepsy is a rare form of epilepsy which affects about 5% of people with the condition. This is about 23,000 people in the UK.

For people with photosensitive epilepsy, a flashing or flickering light can trigger a seizure. A rate of flicker of between 5 and 30 times a second is the most usual frequency range that causes problems, though some people are sensitive to slower or faster flashes.

The intensity and colour of the flash, and whether it occupies all the visual field or not, also affect the likelihood of the flicker to trigger seizures. Sometimes visual patterns (checks, stripes) can have the same effect in some people, particularly if the patterns are moving.

If you do not have epilepsy, flashing lights cannot cause a seizure. Prolonged exposure to flashing light will not cause you to develop epilepsy. A single flash of light can't cause a seizure.

Mysterious condition
Photosensitive epilepsy is a form of reflex epilepsy, where seizures are caused by specific triggers, in contrast to most forms of epilepsy where seizures are not predictable. Photosensitivity is associated with a number of epilepsy syndromes and seizure types. Similar syndromes also occur in some animal species.

Photosensitive epilepsy is more common in children and young people than it is in older adults, and affects more girls than boys. It tends to run in families.

Despite much research, precisely why certain patterns, colours and intensities of light falling on the retina of the eye can stimulate epileptiform discharges in some people's brains is not understood.

Televisions and computer screens
Older computer and television screens (of the traditional, cathode ray tube type, rather than flat screen) may cause seizures because of the flickering of the display. A study published last year found that modern computer screens of this type flicker too fast to cause seizures. Displays that use LCD or flat-screen technology do not have this inherent flicker because the technology behind them is different. Using a smaller screen also reduces the likelihood of triggering a seizure.

Some television programmes and computer software (particularly games) contain light or image patterns that can trigger seizures. People with epilepsy using this material can reduce their chances of having a seizure by making sure they don't sit too close to the screen but instead more than 2m away. Putting a light above the screen, watching in a lit room, and taking a 10 minute break every hour are also good strategies.

In the UK, Ofcom has developed a set of guidelines which set
out which patterns of flashing lights are acceptable and which should not be broadcast. These guidelines are however not binding.

London 2012 branding film
The flickering "snakes" visible throughout the film probably do not take up enough of the screen to cause a problem for many people with photosensitive epilepsy, unless they are also particularly sensitive to the colours or patterns that appear. The static logo itself is also unlikely to cause many people problems. The animated ripples in the pool at the end of the branding film, however, take up the whole of the screen, use bright contrasting colours and move across the screen. This animation could provoke seizures in people with photosensitive epilepsy.

Leigh Slocombe of Epilepsy Research UK said "I find it incredible that this piece of animation for the 2012 Olympics was approved, especially given that there are specific Ofcom guidelines on the broadcasting of patterns of flashing lights because of the problems that they can cause for people with photosensitive epilepsy."

More information
For more information about photosensitive epilepsy, click here to download our leaflet.

We also recommend the following links: an excellent detailed introduction to photosensitive epilepsy and a technical but
accessible article about reflex epilepsies.

Published scientific research on photosensitive epilespy can be found via the global medical literature database, PubMed.

Epilepsy Research UK, PO Box 3004, London W4 4XT Tel: (+44) (0) 20 8995 4781 • Fax: (+44) (0) 870 838 1069 Registered Charity No. 1100394