Cool street lights not a hazard, say scientists

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.









Comments 10

Let's assume a worst-case scenario here and that what they have conclude here is true. That does not alter the fact that this kind of lighting is having a devastating effect on the environment through its effects on living organisms. Of that there can be no shadow of a doubt, and it is well established, and for this reason alone, this kind of lighting should be eliminated. Low colour temperature lighting not exceeding 2200K is the only solution. Furthermore in quiet residential and suburban areas it should be motion operated and subject to an 11p.m. till dawn curfew. It should never be deployed in rural areas in order to maintain the distinction between town and country. In this way the environmental effects of lighting can be cut down to a minimum, and for many who are concerned about our impact on the environment, that is not negotiable. Studies confirming a strong link between light pollution and various forms of cancer have been around for years. There is no smoke without fire. How valid are the studies suggesting that ALAN is not harmful to human health? Is this not just a riposte from the lighting industry in order to maintain the status quo, maximize their profits and keep themselves in jobs at the expense of our health and the environment? We have seen this sort of thing before in relation to lighting and crime, where a "study" confirmed that it reduced criminality, only for it to be discredited later.

Erich is correct IMO. This issue seems unlikely to go away, because people simply seem not to like these 'day-like' lighting schemes. High-blue, high CCT packages are cheaper than more balanced and warmer packages and manufacturers will adopt the most economical solutions when addressing sales, as opposed to technical performance. It is a balance, and major highways may easily justify cooler appearance due to improved colour-rendering and heightened alertness, when cost benefits are factored-in. The wider range of factors within our villages, towns, and cities where people prefer a warmer tone and lower illuminance should not be dismissed - these decisions are often made without consultation with users and the growing adverse feedback on these 'efficient' installations should be taken account of. I believe that there is something about the very high point-source luminance nature of these luminaires that contributes to both visual (and perhaps psychological) discomfort and, like flicker, just because some people do not perceive it does not mean it is not a problem.

Why not use Amber colour LED street lights? They have used them in New Zealand, and some cities in the USA!

The discussion seems to be missing the point that 'daylight' color temperature at night is just not 'normal'. Life is not all about science, it also is about art and comfort. It is not comfortable or artistic to force daylight illumination into a night environment. We are a civilization that has evolved around 'warm' colors of light from fire and we generally find that neighborhoods and roadways that are illuminated with light farther down the spectrum (~2500-3000K CCT, with a balanced spectrum i.e. high CRI / Ca, Ri) is much more pleasant to be around. It sounds to me like someone bought a load of High CCT LEDs and are now trying to force them upon an un-accepting customer.

There is a discussion on this news story in the Lighting Talk group at:

These two reports are talking about completely different things, thus one does not undermine the other. The LRC report is about retinal damage, and it is not new advice, it supports the position of lighting europe saying that LEDs as a light source are not a cause of retinal damage. It is saying the LED sources are safe for use in street lights. The AMA report was about disruption of circadian rhythms, and gives guidance on reducing problems by selecting warm white LEDs to try and reduce any blue light that might disturb the body clock.

As happens so often in these discussions, people are confusing colour Appearance (CCT) with colour Rendering (Ra). In other words, CCT is not necessarily an accurate indication of the spectral distribution of the light source!

Were the organization which published the Blue Light warning were not the A.M.A., that statement would have been ignored by the general public. The document was flawed in research and ignorant of practice. It seems that there was a pre-determined desired result for which corroborating research was sought and thrown together. The LRC doesn't "claim to have scientific knowledge". It does. Impugning one's reputation is a bankrupt strategy of the un-informed.

Your report says the LRC are commenting about blue light hazard, retinal damage, aka chalk The AMA report concerned circadian disruption, (cancer, diabetes... aka cheese

The attempts by many to discredit LED lighting because of the color temperature may also be caused by those who really don't know what they are talking about. Glare from any light source can certainly be a real problem, and certainly some installations are quite clearly not done right. But there is also a segment of society that abhors anything that is stimulating or tends toward promoting increased attentiveness. Thus it is always important to consider the agenda of those who claim to have "scientific knowledge" to back up their claims.

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