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80% of UK school kids ‘at flicker risk’ from old lights

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Four fifths of British school children are having their learning impaired and are at risk from anxiety, migraines, headaches and even dyslexia from flickering lighting, an expert scientist has warned.

Arnold Wilkins, emeritus professor at the University of Essex and a leading expert in photosensitivity and physiology, says distracting flicker in the UK’s schools needs to be addressed. 


Because of the way magnetic ballasts manipulate the 50 Hz sinusoidal waveform of the input voltage, they deliver a light output that flickers at 100 Hz. This frequency is in the danger zone of harmful flicker, which could impair learning.


‘Unfortunately 80 per cent of our schools are still lit with lighting that flickers at 100 hertz’, he told a Lux conference on lighting fixture design in London this month. ‘It causes headaches and its causes anxiety. It’s there all the time. Whether it impairs their learning, seems to me to be plain enough.’

Although people can only directly perceive fluctuations at frequencies up to about 70 Hz, human vision is adversely affected by light fluctuations up to 200 Hz. Visual performance is especially degraded by flicker in the 100 Hz to 200 Hz range and in general, younger people are likely to perceive lower level and higher frequency flicker than older observers.

‘There’s a huge range of susceptibility in the population with those [who get] migraines at one extreme. And it probably contributes to dyslexia but we don’t know for certain.

‘100 hertz should be avoided.’ The solution is to upgrade to high frequency control gear for fluorescent or LED. ‘It’s a simple as that.’

Flicker at 100 Hz is prevalent in older fluorescent light fittings with magnetic ballasts which were popularly installed in schools before the introduction of high-frequency electronic control gear and LED panels. Typically, magnetically ballasted fluorescent luminaires will exhibit flicker of between 10 and 20 per cent of output, and a ‘compact flicker degree’, or CFD, of over 20 per cent.  Prolonged exposure leads to eyestrain, headaches and anxiety.