Epileptic seizures can sometimes be triggered by certain frequencies of flashing or flickering lights, or by certain geometric shapes or patterns. This is a fairly rare condition and is known as photosensitive epilepsy. As epilepsy itself is a common condition it is likely that seizures will sometimes occur by chance while someone is playing electronic games or watching television. For some people this may be a coincidence - they may have had the seizure regardless of what they were doing at the time - and this does not necessarily mean these activities have triggered the seizures. Further investigation may help to determine the cause of the seizures.

Common triggers for people with photosensitive epilepsy

• Watching television, playing video games or looking at other computer graphics
• Having a faulty television or other light source that flickers slowly
• Strobe lights
• Sunlight coming through a line of trees
• Sunlight on water
• Looking out of the window on a train
• Looking at a moving escalator.

A number of factors which contribute to photosensitivity are:

• The frequency (flashes per second) of the stimulus (trigger)
• The intensity (brightness) of the stimulus
• The amount of the person's field of view that is exposed to the stimulus. The more field of view exposed (e.g. viewing larger television screens), increases the chance of triggering a seizure
• Whether the person's eyes are open, closed or blinking
• The background illumination for eaxmple the flickering from a fluorescent tube light could potentially interact with that from a screen, so it is often better to use an ordinary light.
  People with photosensitive epilepsy may also have seizures without flashing lights, although there are some people who only have seizures due to this trigger.