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International Dark Sky Association: Blue Light at Night Threatens Animals and People

Human visual sensitivity is primarily in the green and yellow part of the spectrum and is depicted by the thin solid line. Circadian rhythms are controlled by light emitted within the dashed curve. The color of light emitted by a typical bluish-white 5500 Kelvin LED is depicted by the bold line. A large portion of light emitted by this light source falls outside of the human photopic vision range, and falls within the circadian rhythm curve. IDA recommends limiting blue light emitted below 500 nm, as indicated by the shaded section of the graph.

Human visual sensitivity is primarily in the green and yellow part of the spectrum and is depicted by the thin solid line. Circadian rhythms are controlled by light emitted within the dashed curve. The color of light emitted by a typical bluish-white 5500 Kelvin LED is depicted by the bold line. A large portion of light emitted by this light source falls outside of the human photopic vision range, and falls within the circadian rhythm curve. IDA recommends limiting blue light emitted below 500 nm, as indicated by the shaded section of the graph.

The rapidly expanding use of bluish-white outdoor lighting such as LED and induction/fluorescent, fueled by energy savings, presents a threat to the nocturnal environment, according to the International Dark Sky Association.

According to the organization, bluish light produces high levels of light pollution with significant environmental impact. Specifically, blue light has a greater tendency to affect living organisms through disruption of their biological processes that rely upon natural cycles of daylight and darkness, such as the circadian rhythm. While improving outdoor lighting efficiency, bluish-white light sources escalate the environmental damage caused by artificial lighting.

IDA discourages the use of bluish-white lamp sources with a correlated color temperature above 3000K. If IDA had its way, developers of light sources should be required to refine their products to limit blue light at wavelengths shorter than 500 nm.

  • Mark McClear January 29, 2010, 11:25 AM

    My understanding is that IDA has a potential issue with blue light (defined by IDA as 500nm and shorter wavelengths) on two levels: 1) that “blue light” might cause problematic up-light situations for observatories, etc.; traditional dark sky issues, and 2) “blue light” might cause a disruption to the circadian sleep cycle, which could, in turn, cause heath and other environmental issues.

    The inherent directionality of the LED light source addresses the first point in two ways: A) it makes designing a zero up-light fixture easy (you’d have to work at it to send any up-light from an LED fixture), and B) the total light output of an LED fixture can be a fraction of an HPS or Metal Halide fixture and still meet all the photometric requirements of the lighting design. So, overall, LED should have considerably less up-light, and therefore, present much less of a dark sky problem than traditional sources.

    The circadian sleep cycle point is a completely specious argument. We have measured the SPD of standard cool white LED sources (6,000-10,000K), and compared them to Metal Halide (4,000K). We also compared these spectral distributions to a newer 4,000K LED product (so called, “Outdoor White”). Metal Halide lamps have much more “blue light” in their spectral distribution than any LED source – regardless of CCT — and the Outdoor White LED lamps actually have 41% less “blue light” than a comparable Metal Halide source. If “blue light” were any kind of health issue, it seems like we would have uncovered this already in the several decades that Metal Halide sources have been in broad use – indoor and outdoor – across the country and around the world.

    (to download this data:

  • John S. Richards January 29, 2010, 11:37 AM

    You may want to read US DOE’s reply to IDA’s misguided letter + comments here:

    Note that some IDA members were not happy about the lack of consultation with senior members before this letter was published.

  • Thomas M. Hunter, Jr. PE RA January 29, 2010, 11:49 AM

    There is a fundamental flaw in IDA’s graph that helps their argument. They list the photopic repsonse of the human eye as the pre-dominate visual range. The photopic response is not predominate at night time lighting levels. At low-light levels, the scotopic response is the predominate visual mode of the human eye which is skewed to the blue-white range. This is why white metal halide has seen such popularity. At low light levels, the human eye literally does not “see” the yellow green spectra of sources such as high pressure sodium. Think about the color of moon light and how evolution has influenced human development in order to survive at night.

    I am disappointed in IDA for using the photopic response. It is misleading and severly damages their arguments in my opinion.

  • Mark McClear January 31, 2010, 10:51 AM

    A colleague sent me a note and told me the link I posted did not work (because it had a parenthesis at the end). Here is the corrected one:

    Sorry about that.


  • P. Edward Murray February 2, 2010, 8:03 AM

    I agree with my IDA colleauges in this because it is not just low light levels here but not caring that we are lighting up not just the night sky but the enviroment as well.

    When you fool to much with “Mother Nature” she gets angry.

    And we are destined it seems to reap the rewards much to our dismay.

    Lighting professionals are just lighting salespeople and most seem to only care about their profit margin and nothing else.

    I will continue to speak out against them and to reveal what they truly are.

  • Andrew February 2, 2010, 11:49 AM

    I’m amazed IDA makes statements like this without backing it up with proven research. I realize this debate is a hot topic but after personally attending numerous discussions and presentations on the subject, none of the researchers I spoke with would ever commit to say that their research was “conclusive”. To me, it seems IDA only wants to push their own agenda on seeing the stars at night even from the downtown core of the largest cities.

  • Joe February 3, 2010, 8:00 AM

    You want research? See above link, an excellent compendium of research in this area.

    Ecological Consequences of Artificial Night Lighting
    edited by Catherine Rich, Travis Longcore
    ISBN 1559631295

  • Francis Parnell February 7, 2010, 6:03 PM

    These lighting professionals seem to know a lot more about our health at night than doctors that have spent years doing research on how LAN affects us, not to mention all of the documented harm it causes to the creatures in the natural world. So, with all of their medical knowledge, the next time I get sick I’m going to see a lighting pro!!

  • P. Edward Murray February 10, 2010, 9:15 PM

    If you click on Andrew’s highlighted name, you don’t find an e-mail address but and entity called “Lighting Design Lab”

  • Craig DiLouie February 10, 2010, 9:23 PM

    That’s right, Edward. Andrew is with the Lighting Design Lab, a nonprofit organization dedicated to transforming the Pacific Northwest lighting market to energy-efficient lighting. They are big proponents of daylighting, for example. They’re a great organization.

    Reading these comments, I can’t help but note some of the anger the dark sky community has with the lighting community in general. While the lighting industry as a whole has its faults–most of which stem from what building owners want and how much they’re willing to pay–there are many people in the lighting industry who really care about lighting and its impact on the environment. They would probably point out, as I will now, that good lighting design and light pollution prevention have much in terms of common cause and ground. I think all the lighting people commenting here are saying is that the debate should be based on good science, and the jury is still apparently out on the issue of whether blue light at night is harmful or not. For example, I have heard–but not confirmed, so it’s a rumor–that the IDA has recanted their recommendation about blue light for the time being.

  • P. Edward Murray February 10, 2010, 9:32 PM

    If you click on Andrew’s highlighted name, you don’t find an e-mail address but and entity called “Lighting Design Lab”.

    In other words…

    Andrew is just another lighting salesperson:(

    My point here is this:

    IDA members, Astronomers and others who are sincerely concerned about LIGHT AT NIGHT are the “Canaries in the coal mine” here.

    We are NOT afraid to point out that here on Earth, life developed with The Sun, Moon & Stars as the natural light sources during both day and night and that if we believe that we can haphazardly play with that balance we are in for a very rude awakening indeed.

    That kind of “attitude” gave us all kinds of problems…

    Remember “Love Canal” and Erin Brokovich?

    The simple fact is this…there is NO reason in the universe to light the night sky and in fact it’s wasteful.

    We all need GOOD night lighting and usually that means seeing the ground where we are going not the bellies of Clouds,Birds and Aircraft.

    Perhaps, in a different the Universe of George Jetson, it’s needed…

    And that’s exactly where Andrew and his fellow Lighting Salespeople are.

  • P. Edward Murray February 10, 2010, 9:52 PM

    One last item…

    Some have this idea that it’s just about our “hobby”.

    Just ask your kid or grandkid or neice of nephew if they have ever seen the Milky Way cast a shadow?

    Or The Aurora Borealis?

    Astronomy isn’t just a “hobby” it’s for the soul and it inspires.

    And I want to make sure that every child has that experience..


  • Craig DiLouie February 10, 2010, 9:53 PM

    By your definition, Edward, everybody is a salesperson for something 😉

    But I don’t think anybody here is arguing that outdoor lighting should be wasteful. Best lighting practice entails providing outdoor lighting that achieves the project lighting goals efficiently, placing light only where it is needed and when it is needed, and with good visual comfort (without glare). When best practice is not followed, this is not the fault of the lighting industry as a whole–and often what ends up installed is more a factor of what the owner wants than what the lighting specifier wants. Rather, the contention here appears to be whether advising designers to avoid blue-white outdoor lighting is based on good research. Apparently, the jury is still out on that, and hence the criticism that IDA is getting from the lighting people here–that they would publish a recommendation without developing a scientific case built on solid ground.

    IDA and the Illuminating Engineering Society have partnered on a draft Model Lighting Ordinance that hopefully will be published in final form this year. It is this kind of partnership–the dark sky community working with the lighting community based on common interests–that can really make a big difference in reducing light trespass and skyglow in the nighttime environment.

  • P. Edward Murray February 11, 2010, 12:59 AM

    While I am more than aware that there are far too many “Lighting Professionals” on the IDA Board and that a few lighting professionals are understanding, the fact is that the status quo has changed.

    It’s not 1988 anymore….

    We aren’t “just” nutty astronomers either.

    Fact is that if you look around at new projects you are beginning to see Full Cutoff Luminaires are becoming the norm not the exception.

    Last time I checked, your “Profession” has gotten a “Black Eye” as in the November,2008 Cover Story of The National Geographic entitled

    “The Death of Night”.

    Nope, I don’t think that “we” have to compromise anymore…

    YOU DO and our movememt is growing.

    And I speak for the entire astronomical community.

    BTW, it should interest you to know that I don’t make one red cent doing this either.

  • P. Edward Murray February 11, 2010, 1:08 AM

    And this I will never compromise on….

  • Craig DiLouie February 11, 2010, 2:20 AM

    Yikes. Well, I tried …

  • S Pauley February 11, 2010, 12:32 PM

    To Cree Lighting:

    Can the blue spike of white LED lights be filtered to remove the
    human melatonin suppression effect at 464 nm? What color do you end up with?

  • J. Scarlett February 13, 2010, 11:00 PM

    We live in Seattle Wa. They installed “test” LED streetlights in front of our house and down our street three nights ago. The glare is totally disabling. The individual led lights are exposed, not recessed into the fixture. While there is no “up-light”, the lights from the sidewalk, street and our house are blinding. The shadows are SO black, even just feet away. Seems like we have much more to worry about here than just “blue light”. My eyes actually HURT.
    Our Quality of life is worth a lot more than what Seattle City Light stands to save here. Who stands to benefit?
    Also, out street has had a sudden rash of car prowls since the new lights were installed. Is it the abundance of shadows to hide in?

  • Mark McClear February 14, 2010, 8:46 PM

    Yes, filters can be installed on any lighting fixture, but the point I was making before is that this is not necessary. The new LED sources have 41% less “blue” light than metal halide, even 10% less than T8 fluorescent. If blue light at these energy levels and low-level doses posed any environmental or health problem, I think we’d have found out about it by now. There will always be people who want to outlaw power lines or cell phones because they MIGHT cause cancer; I’m speaking to reasonable people in the lighting community who prioritize saving energy, saving money on maintenance, and eliminating up-light, over the specter of problems that will probably never materialize.

    With regards to the post on the Seattle light test: Yes, sorry to hear about that one… There are plenty of very low quality LED fixtures out there just as there used to be lots of low quality cars on the market in the 70’s. It would be a mistake to paint all automobiles with a broad “low quality” brush just because the first one you tried was a Relient K or a Yugo. We are working with cities and universities to help them write good specifications and RFQs, and filter out the junk that opportunistic peddlers are pushing on the market. See for more details on this…

  • Craig DiLouie February 14, 2010, 10:23 PM

    Thanks for your excellent contributions to the discussion, Mark.

  • Andrew February 16, 2010, 11:34 AM

    Hey all…seems like my comments sparked some additional heated debate. Sorry I have not been on-line recently to follow the discussion but must thank Craig for stating the truth about me and also the lighting industry However, I would also like to clarify a few things:

    1. by trade I am not a salesperson (I do not profit in anyway, shape or form by selling lighting products or anything else.

    2. my background in lighting goes back 19 years as an architectural lighting designer and educator, and yes about 15 years ago did sell product.

    3. my initial comments were based upon my personal experiences such as attending a local IES section meeting which organized a joint discussion with local IDA members. The intention was to talk about what each organization would like to see happen with “sky glow” and the MLO however, all it turned into being was the IDA attendess getting upset that they could only see about 40% of stars from Kerry Park (a Seattle City Park located 1/4 from the Space Needle).

    3. My discussions with several researchers in the study of blue light, from different corners of the world, when asked what the final result was of their findings were they typically came back as saying “non-conclusive”…their words, not mine.

    PS: Thanks Craig for a website and blog that is informative and certainly sparks lively discussion!


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