|Dark-Sky says boo to blue light|
|08 Oct 2009|
|The International Dark-Sky Association has put the red light on blue light, writes Brian Owen. |
|The rapidly expanding use of bluish-white outdoor lighting threatens visibility at night and jeopardizes the nocturnal environment worldwide, according to a statement from the International Dark-Sky Association (IDA).
The statement says that developers of light sources should be required to refine their products to limit blue light at wavelengths shorter than 500 nm. The IDA also discourages the use of bluish-white lamp sources with a correlated color temperature above 3000 Kelvin.
The IDA is a US-based not-for-profit organization aiming to preserve and protect the night-time environment through environmentally-responsible outdoor lighting.
The advisory notes that the “laudable” demand for energy-efficient lighting has resulted in a new generation of electric light sources such as LEDs and induction lamps that emit a cold, bluish white light. Although LED lighting is mentioned specifically, this issue was discussed in an LEDs Magazine interview with Peter Strasser, IDA managing director, who clarified that the IDA is not taking an adverse position towards any specific technology.
IDA states that the bluish light can have significant environmental impact, causing light pollution and sky glow, as well as glare and the compromising of human vision in the aging eye. “In addition, 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.”
As the graph shows, human visual sensitivity is primarily in the green and yellow part of the spectrum (photopic sensitivity curve). Light in the blue portion of the color spectrum below 500 nm, such as that produced by a phosphor-converted “blue-rich” LED, has a limited usefulness to the human eye. This blue light also falls within the circadian rhythm curve.
IDA says that “Some manufacturers and government agencies are misrepresenting the visual effectiveness of these bluish-white light sources, and the environmental impacts are not being considered.” Because of this, the IDA is encouraging government and other concerned parties to support additional scientific research on this subject. “Research will help to understand fully the impact of bluish white light and guide the evolution of lighting technology to protect human health and the nocturnal environment while providing safe and efficient outdoor lighting.”
Strasser told LEDs Magazine that the IDA is continuing its research. “A white paper is currently being distributed for review by a panel of experts. We hope to have it available within 2 weeks,” he said.
At the recent Light Canada, held in Toronto, Peter Strasser and I were discussing LED outdoor installations. The point arose that because of the greater efficacy achieved with higher color temperatures, it appears that utilities such as PG&E are promoting the 6000K color temperature. I recently spoke with Mary Matteson Bryan, who manages the Emerging Technologies program for PG&E. She reassured me that PG&E is not promoting 6000K lighting, and that the decision is solely up to the customer who owns the lighting stock. This was reassuring news for Strasser.
This will surely be a “white-hot” topic at the upcoming IDA Annual General Meeting and Conference to be held November 14-15 at the Wyndham Phoenix Hotel in Phoenix, AZ.
The US DOE webcast “Hitting the Target: ENERGY STAR SSL Outdoor Area Lighting” takes place today at 1:00 pm Eastern, 10:00 am Pacific. LEDs Magazine will be there to see if this is a topic of discussion amongst the participants.
LEDs Magazine will bring you further news on the topic when the IDA White Paper is released, in an interview with Peter Strasser, as well as from the IDA Conference. LEDs Magazine will also be bringing you more background from PG&E in light of their new rate structure and other PG&E program activity.
|About the Author |
|Brian Owen, a contributing editor of LEDs Magazine, is also the Program Advisor to greenTbiz, which facilitates the LED City Toronto initiative. He is actively involved in the development and operation of energy conservation programs for government, municipalities and utilities and specializes in capacity building, commercialization and market transformation. greenTbiz, an ENERGY STAR, Lighting Facts and L Prize Partner, provides energy conservation and environmental awareness programs to the small business sector in Toronto, Canada.|
|Name: bryan Posted: Thu, 07 Jan 2010 19:01|
|it is apparent that the IDA is not taking into account the way the eye uses light at light levels in the Mesopic range, those typically used in outdoor lighting. The peak response of the Rods of the eye are at 507nm, very much in the blue range, the Rods are over twice as sensitive to light at this level then the Cones in the eye at 555nm, the peak sensitivity point for Cone cells. This means that there is much more light needed when using the lamps that have a peek in the 550 or longer wave length visual range. This is more knee jerk environmentalism.|
|Name: g wootton Posted: Sat, 30 Jan 2010 17:01|
|If you read the 'Dark Sky' stuff, it appears that they are anything but neutral -- their white paper includes an extensive infomercial for HPS lighting. Their representation of luminous efficacy issues is rather poor and not well supported (their whitepaper is virtually void of references). I would rather trust the research of the LRC at Rensselaer and other research institutions. It's interesting that the 'Dark Sky' people use spectral curves for out-of-date devices while many modern devices employ much more effective phosphors.
For outdoor lighting the top issues are efficacy, safety and energy efficiency. At least two of these factors play into reduced light polution. It has been shown that using light with the greatest efficacy (and yes it is somewhat blue shifted) allows light levels to be reduced (by as much as 25% compared to HPS) while achieving the same functionality. More importantly, efficiency means putting light where needed and only where needed. The directionality that can be readily obtained with LEDs leads to an optimal use of light. The coverage of well designed LED luminaires is vastly superior in two respects - oblique radiation is much less than with typical'cobra' fixtures; - there is no pronounced downward hot-spot mimimizing the resulting upward reflection of light from the ground. Both of these properties mean that less light is ultimately directed skyward which is likely a good thing. As the data shows, HPS and mercury fixtures produce a very intense downward beam with substantial lateral fall-off with negligible 1/r^2 correction. As a consequence, in order to ensure minimum light levels at the mid-point between luminaires, the overall light level must be increased resulting in unnecessarily high light levels being used. Basically, LED fixtures have been shown to provide better visibility and less glare while also using less light.
When considering the dark sky issue, one should take into account various factors such as surface reflectance, atmospheric absorption and scattering. Clearly, shorter wavelength light experiences greater scattering which results in a more diffuse and lossy atmospheric reflection. Also, atmospheric absorption is slightly higher for shorter visble wavelenghts. Finally, ground reflectance is variable but higher at longer visible wavelengths for pavement, concrete, dirt, sand and even dry vegitation. As I live in the country, I get to experience this when navigating at night since the villages with HPS street lights are clearly identifiable relative to those with mercury based on how brightly they light up the sky.
I'm not sure how one would respond to the circadian rythem issue except that I would consider that anything that keeps you awake while driving at night is probably good for your health. There are also some studies that suggest that extra exposure to blue light during winter months has beneficial effects.
|Name: astro geek Posted: Thu, 19 Aug 2010 00:08|
|Re: Bryan. The reason astronomers are so alarmed by blue lighting is exactly for the reason you give. We use our rods to view nebulae and galaxies. The sort of yellow/orange sky glow you get now is bad enough but as long as you are away from the main conurbations your rods are at least not hugely sensitive to it. I take the point about directionality, but as to people using lights in the Mesoscopic range because they can, I mean seriously, people will just whack up the lighting until it's photopic. Much better that they used red LEDs which don't affect rods at all - no hope of that though. Blue light pollution will be an absolute disaster for astronomy. It's difficult not to be depressed about the relentless increase in street lighting, security lighting, car park lighting, building illuminations and utterly tasteless advertising and light displays. The only ray of hope is the trend for councils to turn down lighting after midnight to try to mitigate rising energy costs.|
|Name: prasad Posted: Sat, 21 Aug 2010 06:08|
|We should switch over to a system of providing pedestrian lighting combined with high-lighting the intersections and pedestrian crossings. The pedestrian lighting system will automatically give the edge of the road lighting, necessary for the visual guidance for the motorist. Pedestrian area lighting also improves the security aspects of lighting. Additional edge lighting & lane marker lighting can be provided in specific cases of need for the benefit of the vehicular traffic.
Whether street lighting is provided or not, the motorist carries his own lighting system.
We started outdoor lighting with short poles just taller than a human being and with 40w to 100w incandescent, moved over to 20w fluorescent tubes and later moved over to greater heights as we got sources of high power & light output in HPMV initially followed by HPSV and these were not available in low power such as 5 or 7 watts that would have been ideal to be fitted on short poles and light the pedestrian areas. With LEDs available satisfying most of these requirements we should revert back to short poles and light up the pedestrian paths instead of the road for the vehicles and satisfy the requirements of safety, energy economy, requirements of Dark Sky. With the typical pedestrian area of about less than a third of the road area, the energy requirement will come down to a quarter. From the security angle, lighting is required to remove dark spots. There are no dark spots on the road; but they are present in the shadows (of trees & other objects) cast from the street lighting system. With pedestrian lighting such dark spots which can harbor anti-social elements will be eliminated.
|Name: duilio Posted: Sun, 22 Aug 2010 18:08|
|The issue of light pollution as any other type of pollution has to be understood from many perspectives. In our case, there is the emission of light due to the staggering amount required by XX century regulations to illuminate the black pavement of streets used by the same millions of vehicles that burn fossil fuels emitting trillions of tons of green house gases and particles into the sky of cities all over the planet. If there is light pollution there is even worst, there is air pollution and its corollary: global warming. The fact that the stars are disappearing is related to the melt down of Ice caps and the glaciers and the disappearance of plankton due to the warming of the seas. The problem is huge and it goes in all directions. The entire planet is in grave danger...
The advent of LEDs has open a window for a real reduction in the use of energy (the US contributes a great deal to the world problem by still burning coal in very inefficient power plants). The IDA lobby is not contributing to solve any of the problems we are facing. In fact their attitude is biased and anachronistic and making thins worst. It will be impossible to turn off lights, its a fact of life. What we need to focus on is instead to redesigning lighting systems in order to become more efficient and better used. The idea of illuminating streets as if they where football fields is a XX century craziness that needs to be reconsidered at length. Maybe the choice is not between artificial lights and stars but Motor Cars or Stars.
|Name: don69 Posted: Sun, 07 Nov 2010 14:11|
|Obviously no one here, apart from Bryan, I think who knows anything about exterior lighting design. The IDA article was so full of mistakes and even more misleading than the other publications it tries to belittle.
The eye is more sensitive to 507nm (blue/green) as previously stated at night time. My thinking is that a light source with a higher content of this wavelength would mean we would need half as much light as we currently do with high pressure sodium thus saving energy tostart with. But more of this wavelength does not mean more blue light being emitted. This blue that you are worried about is the CCT of the lamp when it is above 5000K or so there will be a bluish output. This CCT I would is too high. It is the same principle of using a White Son lamp source (SDW-T)in a supermarket to enhance the colour of red meat but the lamp still looks white; it just has a high red wavelength which the meat reflects. Moonlight itself has a bluish colour and no one complains about that. Has it not occured to anyone that perhaps are eyes are sensitive to yellow by day and blue by night because for most of the time humans have been on the planet they have only had 2 types of light; sunshine and moonlight...|