News, Outdoor, Street

Cool street lights not a hazard, say scientists

A render of a relatively cool colour-temperature LED street lighting installation featuring Siteco Streetlight 20 luminaires.

LED STREET lights with cool colour temperatures are not a hazard, say top lighting scientists.

In a study which appears to rebut concerns raised recently by the US medical profession, a team at the Lighting Research Center in New York –  the industry’s top lab – has found that the so-called ‘blue light hazard’ is not related to colour temperature and can be avoided by controlling the light from the LEDs.

Street lighting campaigner Simon Nicholas says he can see nothing in the LRC’s press statement ‘which might lead to a conclusion that cool street lights not a hazard’.  Pic: David Thrower/Redshift 2016

The authors say it would be a mistake to use colour temperature as an indication of potential blue-light hazard. They say that, for instance, a clear incandescent lamp at 2800K is ‘associated with a greater risk than any white LED source, including one at 6500K’.

Last year, by contrast, the American Medical Association suggested street lights should be limited to 3000K colour temperatures.

The report is certain to be seized upon by local authorities and municipalities who have come under fire from residents and campaigners alarmed by the replacement of sodium lamps with ‘cold’ LED street lights.

But while the LRC study appears to exonerate colour temperature, it says glare need to be dealt with in the usual way by the use of lenses, baffles and diffusers.

The scientists – John Bullough, Andrew Bierman and Mark Rea – say their results show that in the majority of applications, LEDs do not exhibit greater risk for blue-light hazard than other light sources. ‘LEDs present no special concerns for blue-light hazard over other common light sources in typical cases because our natural photophobic responses, such as squinting and averting the gaze, limit exposure to bright light’.

However, street lighting campaigner Simon Nicholas said he could see nothing in the LRC’s press statement ‘which might lead to a conclusion that cool street lights not a hazard’.

Cool street lighting in Rajasthan, India. There are currently 315 million streetlights in the world, and many are being converted to LED. Some  £43 billlion (USD $57 billion) is expected to be spent on LED streets lights by 2026, says Research and Markets. Pic: Ray Molony 2017

‘It’s deeply concerning that the LRC chose to publish a press release on their research without making the research paper itself freely available for scrutiny of the methodologies and conclusions.

‘Once again we have a case of the LRC attempting to discredit the AMA report – and particularly in respect of the use of correlated colour temperature (CCT) as a metric – without providing any alternative metrics of their own. The reality is that CCT remains the only widely used and understood metric, albeit a less than perfect one for certain applications.

‘Furthermore, it strikes me as rather hypocritical for the LRC to denigrate the AMA for its use of CCT when it is widely accepted that whilst radiance is also a significant factor in calculating photobiological risk, it also holds that for directly comparable sources, the blue light hazard risk also increases with CCT.

‘One has to question what  the LRC’s real agenda is? Is it to promote better street lighting or to simply to try to score points against the AMA for having the temerity to point out to the lighting industry what the general public can see quite plainly –  that there are serious issues with LED street lighting of which blue-rich spectral content is just one of many.’



  • The colour temperature of street lights, the blue light hazard and glare will be discussed by US expert Bob Parks of the Smart Outdoor Lighting Alliance at LuxLive 2017 on Wednesday 15 November. His presentation – entitled How to specify street lights like a pro – takes place at 3.30pm in the Smart Spaces Conference theatre. The conference is open to street lighting specifiers and re-registration is required HERE.