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New streetlight design curbs light pollution

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April 26, 2013

Schematic of the new street lamp

Schematic of the new street lamp

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For astronomers, a well-lit city means a sky unavailable for study. Worse, light pollution is blamed for affecting bird migration, sea turtle hatching, and wildlife mating and feeding routines. Researchers at National Central University, Taiwan, and Unidad Academica de Fisica, Universidad Autonoma de Zacatecas, Mexico, have attacked the problem with a new LED street lamp designed to shine only where needed, without splashing into unwanted areas, as a way to reduce light pollution while providing better lighting.

Current street lights often use high-pressure sodium or mercury lamps, and can spill light in unwanted directions, resulting in glare, non-uniform light patterns, upward-reflected light, and wasted energy. In some cases, nearly nearly half the light is lost by the light flooding horizontally and vertically, and conventional street lamp design has trouble adapting to different street lighting layouts, whether the lamps are set in the middle of the road, above it or in a zigzag pattern.

The research team proposes a new LED street lamp design based on a three-part lighting fixture, with the first part containing a cluster of high-efficiency LEDs. These use Total Internal Reflection (TIR) lenses, which focuses the light into parallel rays. The LEDs are mounted inside a reflecting cavity that helps keep the light from scattering and, as it leaves the unit, light is passed through a diffuser to reduce glare. According to the team, this design allows the lamp to project a uniform rectangle of light over a given area.

Continental United States as seen at night from the Suomi NPP satellite (Image: NASA Earth...

The LED street lamp was studied in simulation to determine the spread at a distance of 10 meters (33 ft) from the light source. This was measured by the team as the optical utilization factor (OUF), which describes the relationship between the flow rate of light at the target and the flow rate of light coming directly out of the LEDs. A higher OUF indicates better performance.

The simulation showed an OUF of 51 to 81 percent, compared to a conventional street lamp’s “excellent” performance of 45 percent. The proposed street lamp loses only two percent of its light as direct pollution and reduces energy consumption by 40 to 60 percent. The team also claims that the new lamp is relatively easy to fabricate because it only has four parts, with the LED component already an industry standard.

The team plans to have a working prototype within three to six months, followed by practical installations of the new street lamp as early as next year.

Source: Optics Express

About the Author
David Szondy David Szondy is a freelance writer based in Monroe, Washington. An award-winning playwright, he has contributed to Charged and iQ magazine and is the author of the website Tales of Future Past.   All articles by David Szondy
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7 Comments

Finally someone take a smart action towards these problems! It will also reduce the reflections when driving in rain, improving sight and safety. Another possibility is also to make the main street LED light activated by motion and light detectors, saving a lot of energy on streets with less traffic. Only some guiding LEDs can be on continuously. This is not possible with the current types of lamps that need a long warm up time. Communication from lamp to lamp can light them up at a distance in front of a vehicle and then shut down when vehicle have passed.

SoundRacer
26th April, 2013 @ 02:38 am PDT

The city of San Jose used Low Pressure Sodium lamps because they had a nearby observatory and the LPS lamps offer low light pollution and high efficiency. The only real downside to them is that since they emit such a narrow spectrum of color (yellowish orange or 586 - 589 nm) it can be hard to correctly judge colors of objects illuminated by them. The limited spectrum also doesn't mess with your night vision as much as lights that emit a fuller spectrum of wavelengths.

They use high-pressure sodium (HPS) or mercury in places like heavy tourist areas and major highways only. The background section of this document has more data: http://www.sanjoseca.gov/DocumentCenter/View/3864

I live near one of the best dark sky sites on the east coast (read: middle of nowhere) and I thought about trying to get my town try LPS. Filtering the physical direction of light seems like it would partly solve the problem though as long as it doesn't create a danger by giving too limited of a view of potential hazards just off the roadway.

It's probably possible to combine both approaches though. A broader spectrum than LPS that allows better color perception could be a good compromise. The danger of bright white lights at night is they mess with your night vision and you must then illuminate everything in a sort of light pollution arms race.

Daishi
26th April, 2013 @ 02:39 am PDT

Good to see but how much light pollution is reflected light? Generally it would be less of a problem than direct light but I presume it's a significant factor. To curb it, I reckon more, smaller street lamps is the answer Obviously we don't want more metal poles messing with the sidewalk feng shui but more cool, low powered downlights could be incorporated into trees, existing structures etc.

Hogey74
28th April, 2013 @ 09:32 pm PDT

Proper shielding/lenses on newer fixtures already take care of light pollution from a scattering (horizontal and upward) perspective. Reflected light will always be a problem since that is how we see objects. The major driver in the non-use of LED lighting has been cost. And there may be some questions about claimed longevity, based on some of the traffic lights in my town.

Bruce H. Anderson
30th April, 2013 @ 08:47 am PDT

The problem with LED is that it is high in the blue spectrum. In fact, its efficiency looks best on paper (and so easier to sell to municipalities) when using the numbers high in the blue spectrum. Blue light at NIGHT, without a doubt, is the absolute most harmful wavelength to the environment, ecosystem and human health. Blue light during the DAY is healthy and essential. LED manufacturers need to figure out the best way to filter out the blue. Until they do, I will fight them.

Audrey Fischer
30th April, 2013 @ 11:37 am PDT

I take strong issue with this statement: "For astronomers, a well-lit city means a sky unavailable for study."

Wrong! It's the OVERLY-lit city that is the problem. Outdoor lighting at night is irresponsibly out of control and causing harm to human health, the environment and ecosystem while significantly adding to the taxpayer burden with a US annual impact over $100billion. The proof of "well-lit city" is starlight. It is possible and essential that cities commit to satisfying the necessities of citizen & business lighting needs while dramatically reducing light pollution and restoring starlight.

Audrey Fischer
30th April, 2013 @ 11:56 am PDT

If you live in a city, you don't really need to see the stars. No astronomer would ever build an observatory near a city, for two reasons: light pollution, and heat emissions. We do need to see where we are going at night in the city, for safety reasons, and lighting makes a city attractive to look at. Go into the countryside when you want to look at the stars.

David Colton Clarke
15th May, 2013 @ 04:03 am PDT
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