Strobe lighting at music festivals can increase the risk of epileptic seizures, researchers have warned.
The Dutch team said even people who have not been diagnosed with epilepsy might be affected.
Their study was prompted by the case of a 20-year-old, with no history of epilepsy, who suddenly collapsed and had a fit at a festival.
The Epilepsy Society said festivals should limit lighting to the recommended levels.
Epilepsy is a condition that affects the brain. There are many types, and it can start at any age.
Around 3% of people with epilepsy are photosensitive, which means their seizures are triggered by flashing or flickering lights, or patterns.
The Health and Safety Executive recommends strobe lighting should be kept to a maximum of four hertz (four flashes per second) in