Fighting Light Pollution
Solar concentrators help eliminate unnecessary light in national park.
Yosemite National Park in the USA offers stunning views of mountain vistas during the day and star-filled skies at night. This view often includes the Milky Way — invisible to almost one third of Earth’s population due to light pollution.
Artificial lighting is restricted in Yosemite, but some areas in the park require lighting, such as parking lots and pathways between buildings. Light pollution can not only have a negative effect on visitors’ experiences, but it can also change the circadian rhythms of the park’s flora and fauna.
SPIE member and University of California, Merced (UC Merced) graduate student Melissa Ricketts has found a solution — by turning one of her professor’s inventions upside down. Ricketts is a member of UC Solar, a multicampus research institute headquartered at UC Merced and headed by Roland Winston, an SPIE member and pioneer of nonimaging optics. Winston’s compound parabolic concentrator (CPC) is a key piece of solar-collecting equipment in the emerging solar energy industry.
Ricketts has developed a way to make Winston’s CPC emit light rather than gather it.
“It’s the reverse of the solar collector,” Ricketts said in an interview with UC Merced’s University News. “We can make a perfect square of LED light, or a circle, or whatever shape works best to illuminate only what needs to be illuminated. I call it ‘prescribed irradiance distribution.’”
Ricketts has been working with Steve Shackelton, a UC Merced staff member and former Yosemite chief ranger, on what they call “The Sand Pile Project.” Although most of their work is done in the lab, designs are occasionally tested in Yosemite, about 90 miles from the university campus, on a large pile of sand that snowplow operators spread on the park roads when needed. The park needs to keep the sand pile well-lit so it can be accessed at any time, but lighting should have minimum effects on the surrounding areas.
Yosemite is cautious about introducing new technology into the park, wanting to combine best practices with maintaining the smallest human footprint possible. But the park has been supportive of Ricketts’ research toward managing light by letting her use the area as a test where her work could eventually have global implications.
“We’re hoping to show the park we can eliminate the unnecessary light,” Ricketts said. She’s currently seeking funding to make the project viable for Yosemite and other parks.
Ricketts presented her research on reducing light pollution at SPIE Optics + Photonics in August.
The paper, “Nonimaging optics in lighting to reduce light pollution,” coauthored with Winston, Lun Jiang, and Jon Ferry, shows how nonimaging optics and LEDs can be used to control light to achieve a desired distribution of illumination.
Called “prescribed irradiance distribution,” the light dispersal has a sharp cutoff such that light leakage is minimal.
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