DO YOU love watching sunlight dancing on water or flickering through church railings? Well, you鈥檇 better be careful, because there鈥檚 a dark side to light.
Those dancing images can trigger flicker illness, a term coined by researchers at the University of Rochester School of Medicine and Dentistry in New York to describe extremely unpleasant symptoms ranging from the dizziness, vertigo and nausea associated with motion sickness, to the seizures of photosensitive epilepsy.
So what exactly is going on in the brain, and how many people are affected? No one knows, but there are some clues to answer the latter. In 1953, a study exposed people with no history of epilepsy to flickering light. About 28 per cent of them experienced nausea, headaches or vertigo, while 5 per cent had a seizure. Photosensitive epilepsy is thought to affect 1 in 4000 people, but the true incidence may be much higher because many people do not know they have it.
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The Rochester researchers cite an example where an air ambulance was called for one unlucky man who had nearly cut his foot off with a lawnmower. As if his injuries were not bad enough, sunlight flickering through the helicopter鈥檚 rotor blades triggered a seizure.
Flicker illness can be induced by lots of everyday circumstances, including light flashing through bicycle wheels or sunlight flickering through poplar trees planted in rows, which can affect passengers in passing cars and trains.
Unfortunately, the range of flicker frequencies that can cause a reaction is very wide. The most dangerous flash rates are between 20 and 30 hertz, but the range stretches from just 3 hertz right up to 60 hertz.
What should be done? The flicker illness researchers say air ambulance crews could cover the eyes of patients, who may be staring directly through the helicopter鈥檚 rotor blades. But in a world of flashing lights, eliminating other triggers is difficult.
Strobe lighting is perhaps the best regulated, but what about a more everyday trigger: television? Earlier this year, a flickering logo used in an advert for the London Olympics in 2012 induced seizures in 30 viewers. And what of the Japanese children who, in 1997, were watching a Pok茅mon cartoon where an explosion was illustrated by rapidly flashing red and blue colours? Of the 685 children taken to hospital with symptoms of flicker illness, 560 had suffered seizures.
鈥淭he 2012 Olympics logo caused seizures in 30 viewers鈥�
There鈥檚 no excuse for film, game and TV companies 鈥� especially in the UK. Graham Harding, a leading expert on photosensitive epilepsy, helped develop a scanner to check footage for images likely to cause seizures. And then there鈥檚 the web to consider鈥�
There is a strong case for more research to find out why that beguiling flicker makes so many of us feel so ill. In the meantime, watch out for those Christmas tree lights next month.
The Human Brain 鈥� With one hundred billion nerve cells, the complexity is mind-boggling. Learn more in our cutting edge special report.
