City denies colour temperature switch is due to protests

SEATTLE has become one of the first major cities to announce a switch to warmer colour temperatures for its street lights.

The municipality says it will replace its original 4000K LED luminaires with warmer 3000K following protests from residents.

However, the public utility responsible for the street lighting network, Seattle City Light, denies that the switch is in response to residents’ concerns or the widely-publicised warning by the American Medical Association in 2016 concerning the impact of high-intensity LED street lights on human health and wildlife. The AMA recommended that colour temperatures should not exceed 3000K.

The colour temperature of street lights has become a major issue, partly for the perception that cooler colour temperatures such as 4000K and even 5000K deliver more harmful blue light. Pic: Dominic Alves via FlickrMedia Commons 2017

The colour temperature of street lights has become a major issue across the world, partly for its glare and partly for the perception that cooler colour temperatures such as 4000K and even 5000K deliver more blue light, which has become associated with poor sleep and even higher rates of cancer.

Scott Thomsen of Seattle City Light said that while he is sceptical of the AMA’s conclusions, he wouldn’t deny that blue light can be bad for sleep. However, Thomsen believes the blue light from televisions and devices such as smart phones is far more of a concern than that produced by street lights.

Thomsen also said that the American Medical Association’s recommendations played no direct role in the decision to change the specification of the city’s luminaires.

Earlier this year a study by the Barcelona Institute for Global Health and the University of Exeter linked blue light from LED street lights to a ‘significant increase' in the risk of breast and prostate cancer.

It found that participants living in large cities with heavy exposure to blue lights at night had double the risk of prostate cancer and 1.5 times higher risk of breast cancer. This was compared to populations with less exposure to blue light.

The researchers found the bluer the light emission that people in large cities were exposed to, the higher the risk of cancer. The study also found that people who lived in homes with darker rooms, by using window shutters for example, had lower risk than those who did not.

The study included medical and epidemiological data of more than 4,000 people between 20 and 85 years of age in 11 Spanish regions. It particularly examined Madrid and Barcelona.


  • Urban lighting is the subject of the new Safer Cities Conference which takes place on Wednesday 13 November and Thursday 14 November 2018 at the LuxLive exhibition at London ExCeL. For more information on the event, click HERE.

Comments 9

The differences are many for shifting towards 3000'K in scotopic vision, so it's a matter of many priorities : public safety, comfort, cost, acuity, environmental impact, mood effects. Each has different weighting factors and usually the cost of making a change has to be weighed with the cost of not doing the change. One major factor for making urban changes that can affect payback period is tourism revenue, state of mind.but most importantly, the chances of getting re-elected. It is state of mind of residents who prefer the comfort of warmer night lighting over the benefits of acuity and safety of 4500'K and how politicians want to get re-elected by greasing the squeeky wheels to approve the costs nodding that must be some scientific reason like the migration habits of bats.

Probably more to due to the $99.00 Cree Streetlight program than color temperature.

The other thing that is usually unclear in these articles, is based on the fact that there are many ways to get LED light of a particular CCT (color temperature), whether the CCT is 3000K (warm white) or 4000K, or 6500K. As an example, with an RGB LED array, I can blend the three LED wavelengths to get essentially any color temperature of white light. But the actual spectrum consists of peaks at around 470nm (blue), 530nm or so (green), and 625nm or so (red). So blue light is present, regardless of the CCT, albeit with differing intensity. That said, most white LEDs use blue LEDs to excite yellowish phosphors, so you have a narrow peak of blue light, along with a broad "hump" of yellowish light. Depending on the exact phosphor formulation used, and how thickly it is applied over the blue LEDs, determines the color temperature of the resulting white light. But again, there is always a blue "spike" in the spectrum, from the underlying blue LEDs. (As one of the above commenters stated, the exciting LEDs don't have to be blue, they basically need to be of a wavelength that is shorter than that of the phosphors. They could be indigo (lower wavelength than blue), or even UV (even lower). In order to do solid experimentation, you really need to look at more than the color temperature of the light, you also need to look at the specific spectral components - in short, how is the color temperature derived. Is the effect based solely on the perceived color temperature? Or is it based on the presence of specific wavelengths, or wavelength ranges? A 3000K LED light still has blue light as a component, whereas an incandescent bulb of 3000K does not. Do these two versions of 3000K light sources behave the same in terms of sleep patterns, or even the alleged affect on cancer incidence? Impossible to tell from the articles.....

Most of the major cities in the US are moving towards 3000K (or lower), including Los Angeles (originally 4000K), Phoenix (2700K), Chicago (3000K), Washington DC (3000K and 2700K). Most of these are late adopters....the problem for early adopters is that they originally chose 4000K or higher because of significantly higher efficacy that is no longer true. The problem with LED street lights is that once installed, they need to be in service for 15+ years to amortize the investment with energy savings. Cities like LA that take several years to convert will have a mixture. Seattle was an early adopter, and replacing LED lighting early is a challenge economically. I would argue that while the AMA position played a significant role in calling attention to lower CCT lighting, the reduced glare and desirable appearance are catching on equally as the real reason for shifting once efficacy differences became small.

I believe that the reason for the switch is the efficiency of the warmer while light lamps as compared to those with cool white in terms of lumens per watt. There is about a 15% difference in efficiency between the warm while and cool white LEDs.

I'd recommend everyone read the comments section of that 27 April "Study Links LED Streetlights to cancer" article. The Seattle article references it, propagating what was clearly flawed science. Blue light (or any light) influences are about spectral compositon, dosage, duration and timing. Definitely as it relates to retinal ganglion cell (non-visual ) activation, and perhaps as it relates to long-medium-short cone activation. In the article Simon cites, the researchers once again prove that their strength is not in physiology of color with the statement, "Using this Opn1mwR model, we first established a background lighting condition (using a three-primary LED system), whose spectral composition recreated a wild-type mouse’s experience of natural daylight". Recreating broad-spectrum sunlight with just red, green and blue is very close to laughable. Fine to create an impression of color, but sadly short of a realistic spectrum. Use a purple pump LED to create 5000K and 3000K streetlamps with 0 blue content, and you would still hear screams from the blue-ists about how the cool one is killing everyone. Hype 1, Science 0. Still a lot to learn.

At last they are paying attention to the people who have to live in these environments . I would like to put one of these outside every bedroom of the decision makers and see how they feel . I see people are trying to suggest that the colour temperature from natural light is the same as artificial light because it has the same colour temperature . That is science gone mad. For gods sake its completely different and if you can t see the difference between nature light and an electronically produced source that you should not be specifying such things

Bruce, Had it not occurred to you that the "basically same colour temperature" that you see out of your window TODAY is natural DAY light. Why on earth do you think that flooding the planet with what is effectively "artificial daylight" at night time is a good thing? Here's some interesting research which might inform your thinking on the subject: As for Scott Thomsen's claim that the " American Medical Association’s recommendations played no direct role in the decision to change the specification of the city’s luminaires", the immortal words of Mandy Rice-Davies spring immediately to mind ........ ("well he would say that, wouldn't he?")

It will be interesting to find out why Seattle decided to specify 3000K street lamps, but inappropriate to attribute reasons for the decision to anything other than an aesthetic choice at this point. Cities used metal halide lamps that leaned heavily blue before HPS lamps, with their amber appearance, became common. Human scotipic sensitivity favors daylight color temperatures, and the earliest LEDs were similarly balanced that way. Without better studies that indicate otherwise, I would be cautious suggesting that there’s a link between daylight CCT sources and health problems. After all, just look out your window today. What you see is the basically the same color temperature as the “blue” streetlights.

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