We really don't know. What we do know is that between one and five percent of people with epilepsy seem to be sensitive to flashing lights. That is called a strobe effect. It is one of the reasons we flash lights at patients during EEG testing, because it may bring out epileptic activity. Some encephalographers believe that people who experience seizures while watching flashing lights always have generalized epilepsy.
Researchers think there is some hereditary component to it related to the way the brain is wired.
In my experience, more people complain of bright, flashing or florescent lights than actually have seizures set off by those lights. Those who have light-sensitive epilepsy will usually have epileptic activity appearing on the EEG when lights are flashing. A. Photosensitive epilepsy can occur at any age. However, it usually begins with younger children, normally between the ages of five and 10. Then they might have their first seizure set off by flashing lights.