Starlight VS. Streetlight
ensuring the LED revolution doesn’t worsen light pollution in the Valley
All over the world, the stars are vanishing.
This is not the plot to a sci-fi thriller: It’s reality, as light pollution from our streets, businesses, and dwellings squeezes out the comparatively faint light of distant stars, planets, and galaxies. According to study published this month in the journal Science Advances, this “skyglow” prevents fully 80 percent of Americans from seeing the Milky Way at night.
And this has more than just aesthetic implications: At worst, light pollution can make it difficult for scientists and hobbyists to study the universe, it wastes energy, it can disturb human sleep cycles, and it can confuse wildlife.
EYES ON THE SKIES
“You don’t need to light up Clairemont Avenue like it’s a Friday night high school football game.” – Mike Brown, Chippewa Valley Astronomical Society
Now that Chippewa Valley communities are beginning the transition from traditional high-pressure sodium streetlights to more efficient light-emitting diodes – or LEDs – dark-sky advocates are speaking up to ensure that new technology makes the light pollution problem better, not worse.
“You don’t need to light up Clairemont Avenue like it’s a Friday night high school football game,” explains Mike Brown, president of the Chippewa Valley Astronomical Society, whose members gaze at stars both from the Hobbs Observatory at Beaver Creek Reserve and their own backyards. Brown recently sent a letter to members of the Eau Claire City Council encouraging them to keep the night sky in mind when making choices about LED streetlights in the coming years.
From the Hobbs Observatory, a bright dome of light pollution surrounding the city of Eau Claire can be seen in the western sky. When amateur astronomer Bill Childs of Eau Claire first became involved in the society 30 years ago, light pollution wasn’t much of a problem at the observatory 13 miles out of town; now stargazers don’t even bother to look for objects along the western horizon. Just as surely as felling a forest or dumping waste into a river, flooding the night sky with excess light causes the loss of a natural resource, Childs explains.
DEGREES OF DIFFERENCE
Concerns about keeping skies dark used to focus on the number of outdoor lights, their brightness, and their direction. Traditional streetlights, for instance, were often poorly designed and illuminated the sky above as well as the street below. With the advent of LED lighting, worries about light color have been added to the mix.
To explain why, here’s a bit of science: The color temperature of a light – whether our eyes perceive it as “cool” or “warm” – is measured in degrees Kelvin. Traditional high-pressure sodium streetlights measure at about 2,200 degree Kelvin, giving off a reddish-orange glow. By contrast, full-spectrum LED lights are 4,000K or higher and include more blue light, making them appear “cooler” and more like daylight. When it comes to light pollution, this can be a problem, because blue light scatters more easily in the atmosphere. That explains both why the sky is blue during the day and why LEDs with a blue component cause more light pollution at night.
In addition, the old-fashioned high-pressure sodium fixtures typically produced light in a very narrow spectrum, which made it easy for astronomers to filter out.
Leah Ness, transportation engineer for the City of Eau Claire, said most of the more than 2,000 city-owned streetlights still need to be upgrade to LEDs, a process that won’t begin until at least 2018. (There are a smattering of LEDs on city-owned poles in town, including on First Avenue, Grand Avenue, a few trails and intersections, and one spot on Clairemont Avenue just west of Keith Street.) In 2009, she noted, the City Council passed an ordinance requiring that the city’s outdoor lighting follow the best practices of the Illuminating Engineering Society of North America. In 2011, that group and an allied one, the International Dark-Sky Association, created a model ordinance designed to help municipalities reduce light pollution. However, LED technology has changed rapidly in the past five years, and the model ordinance makes no mention of LEDs. Currently, the International Dark-Sky Association advises that outdoor lights be 3,000K or less to minimize pollution from blue light.
Earlier this year, Xcel Energy replaced approximately 5,000 streetlights in the Eau Claire and Altoona area with LEDs that put out light at 4,000K – in other words, light that is “cooler” and “bluer” than recommended by the International Dark-Sky Association (although they meet older standards for reducing light waste).
Xcel spokeswoman Chris Oullette said that the upgrade was done at no cost to the city. (Xcel owns and maintains light poles in residential neighborhoods and less-busy streets, with the City of Eau Claire is responsible for poles along more heavily-traveled thoroughfares such as Clairemont Avenue and Hastings Way). The upgrade will save the city between $40,000 and $50,000 annually on its electric bill, Oullette said. There have been only a handful of customer complaints about the new lights, and they were about their orientation, rather than their color, she added.
LOWERING THE TEMPERATURE
Nonetheless, Brown and other members of the Chippewa Valley Astronomical Society hope the City of Eau Claire and other local municipal governments make different choices when selecting LEDs. They say that 3,000K LED lights are available that would also save energy but produce less light pollution.
Brown notes that aerial photos from Xcel demonstrate that most of the light pollution in Eau Claire is coming from main thoroughfares (such as Clairemont Avenue) and commercial areas. Therefore, the decisions the city makes about lighting over the next few years have the potential to significantly impact overall light pollution. He hopes his group is able to illuminate policymaker’s decisions and help keep the night sky as dark as possible.