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Street light flicker is new hazard, says watchdog

If local authorities replace mercury and sodium street lights with LEDs purely on the basis of energy efficiency and cost, then it's possible to end up with installations that may not be fit for purpose, Public Health England says in its annual medical report.

FLICKER FROM LED street lights could be becoming a health hazard, the UK government’s official health watchdog for England has warned.

Public Health England says in its annual medical report, published this month, that the phenomenon is ‘of concern’.
Some of the LED sources assessed by Public Health England and others vary in illuminance at a frequency of 100 hertz. At the extreme, the LEDs switch on and off 100 times per second. ‘This is of concern for a number of reasons,’ writes John O’Hagan, group leader at PHE and a visiting professor in laser and optical radiation safety at Loughborough University.
‘Some people seem to be very sensitive to this light modulation, resulting in headaches, migraine and less specific feelings of malaise. However, most people will experience phantom arrays.

‘[This] happens when you move your eyes quickly when behind a car with its brake lights on, particularly in the dark, and there is the risk of a stroboscopic effect. This effect may manifest itself as moving objects appearing to jump, rather than move smoothly.
‘More seriously, rotating machinery, which could include the blades on a food mixer, may appear to be stationary if the rotation rate matches the modulation rate or is a multiple of it.’
O’Hagen says glare and blue light are also concerns with LEDs. ‘Some LED installations, however, have LED chips visible, which can form a source of glare.
‘An extreme example is daylight-running lights on cars. These are clearly visible to other road users and pedestrians. At night, if they do not dim, they can be very dazzling and more so for young children who have higher transmission of light through to the retina and older people who will suffer from scattering of the light, particularly in the lens of the eye.
‘This means that older drivers, in particular, will be dazzled by oncoming vehicles with the risk that they may not see hazards until too late. The problem is exacerbated by fog.
‘Local authorities have been replacing mercury and sodium street lights with LEDs. If this is done purely on the basis of energy efficiency and cost, it is possible to end up with installations that may not be fit for purpose.
‘Some streetlight luminaires have LED sources that can be seen physically projecting below the luminaire, becoming a glare source or light pollution. The light spectrum may be enriched in the blue, which may be beneficial for keeping drivers alert, but many people will find the light uncomfortable.
‘High levels of blue light are known to cause damage to the retina in the eye. This only tends to be a problem for blue LEDs and not for white-light LED sources containing a blue LED and a yellow phosphor. It’s possible to have LED street lighting that directs the light only to the areas that need to be illuminated, minimising the light that goes in the sky. They can also be provided in a range of colour temperatures, where warmer colours are likely to be more appropriate for populated areas’.


  • Light quality will be one of the issues explored in the Safer Cities conference taking place at the LuxLive 2018 exhibition at London ExCeL on Wednesday 14b November and Thursday 15 November 2018. More information HERE.