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SPIE Professional October 2010, Bonus Web Content

Light Pollution

Scientists fight stray emissions and glare from lighting fixtures.

By Beth Kelley

Unaided view of the night sky from Palomar mountain, photo by Scott Kardell

Light pollution is more than just a hazy-looking glow in the night sky. Excessive and stray light is a waste of energy, interferes with astronomical observations, disrupts ecosystems, affects animal migration and navigation, and can cause adverse effects on human health and safety.

Unfortunately, light pollution is not seen as a serious issue in many places, and more and more artificial light is entering our atmosphere every year. Now astronomers, lighting engineers, and dark-sky advocates are taking action against light pollution, raising awareness with public education, designing better lights, and getting political.

"Dirty" night sky

Before the industrial revolution, there wasn't much artificial light in the world. Today, most of us in the developed world have access to light 24 hours a day. These hundreds of millions of lights usually send light out in all directions, including up into the sky at night. The major sources of this light pollution include streetlights, advertising signs, skyscrapers, factories, and illuminated sporting venues.

Traditional acorn-shaped streetlights (left) scatter light in all directions, including up to the night sky where illumination is not needed or wanted. A better streetlight has a shield on top to reduce light pollution.

"All of the major urban centers across the world have severe amounts of light pollution," says Scott Kardel, public affairs coordinator at the Palomar Observatory near San Diego. "It is estimated that 20% of the world's population can no longer see the Milky Way from where they live," he says.

According to the First World Atlas of Night Sky Brightness, the night sky is brighter than a first-quarter moon for 96% of the European Union population, 97% of the United States, and 50% worldwide.

The U.S. National Parks Service Night Sky Team has documented light from over 200 miles away affecting night skies. Light pollution or "light trespass" has been growing by 4% each year. Some suggest that the night sky will be unviewable in the contiguous United States by 2025.

Wasted resources

There are many repercussions for all this misdirected light. One is wasted energy. The International Dark-Sky Association (IDA) estimates that 22% of all energy produced in the U.S. goes toward lighting, and that one-third of that lighting is wasted at an annual cost of about 30 million barrels of oil and 8.2 million tons of coal--amounting to a total of about $2 billion. The oil alone adds to global warming, generating 14.1 million tons of CO2 per year into the atmosphere, according to the U.S. Department of Energy.

Reducing the light pollution generated from just public outdoor illumination would have a significant impact on energy conservation, the DOE says.

Wildlife impacts

Another concern is the effect excessive and misdirected artificial light has on ecosystems and migratory animals. There are hundreds of species of birds that migrate each year and use the night sky to help guide them. Confused by artificial lighting, many thousands die flying into buildings or from exhaustion due to "misnavigation."

Sea turtle hatchlings navigate by the brightest light, which used to be the sun or moon. Now the lights from beachfront properties can turn the hatchlings around and get them lost on their way to the sea.

Emma Stone, a student at the University of Bristol (UK), has shown that high-pressure sodium streetlights can divert lesser horseshoe bats from their nightly routes. Bryant Buchanan, associate professor of biology at Utica College, NY (USA), found that exposing South African clawed frog tadpoles to one lux every night (not much brighter than a full moon) for 37 nights slowed their maturation process.

"There are a number of wildlife impacts, but probably the most pressing is how it affects human health," says Bill Wren, special assistant to the superintendent, University of Texas at Austin, McDonald Observatory (USA). Humans have a circadian rhythm that is dependent on natural light. Without it, we suffer from sleep deprivation and a lowered immune system.

"It's between the dark hours, about 11 pm - 3 am, that our immune systems are most active," Wren says. "And what informs your body that it's time to do that regenerative work is whether light is striking the retina and visual cortex."

Night-shift workers have an increased risk of certain types of cancers and chronic diseases. Light pollution has also been correlated with suppressed melatonin production and increases in cancer rates, particularly in older women. A study on premature newborns suggested that most receive too much artificial light in hospitals, affecting their immune systems and sleep cycles.

People often cite safety as a reason for leaving lights on at night, but it actually can cause more of a safety hazard, since light pollution causes diminished nighttime visibility. "If you have a poorly shielded light fixture that's overly bright, like over a crosswalk, it actually makes it harder to see," Wren says. This is particularly true for middle-aged and older drivers, he says.

Where's the Big Dipper?

Probably the most commonly known consequence from light pollution is that it affects astronomers, pilots, and anyone who needs--or wants--to see the stars and planets at night.

"The night sky is something of enormous wonder," says SPIE Fellow Roger Angel, Regents Professor at the University of Arizona Steward Observatory. However, he says, "Most kids have never really even seen it because you don't see it from cities."

That's a problem because it's important to interest young people in the natural world, he says.

Although astronomers can travel to sites where light pollution isn't such a problem, established observatories near big cities struggle against seeing through the glow from streetlights, porch lights, and other light clutter.

"The use of broadband light sources has a great impact on spectroscopy," an important astronomical tool, says Kardel. The murky haze of light pollution blocks all wavelengths of light, making it impossible to see the night sky, even with astronomical instruments.

Flip the switch

Fortunately, there are easy solutions to this problem. One is simply turning off lights. Some places in the UK and elsewhere are initiating "dark hours" where all lights are turned off for a few hours each night.

Another way to limit light pollution is by controlling the angle in which light is directed from a luminaire. The "acorn" style streetlight is an example of a device that emits light in all directions, and it is one of the worst light polluters. Light trespass can be reduced by limiting the amount of light emitted from a fixture more than 80 degrees above the nadir (the angle pointing directly downward from the light source). The Illumination Engineering Society (IES) of North America classifies different non-polluting luminaires based on their angle: full cutoff (0%), cutoff (10%), and semi-cutoff (20%).

The Dark-Sky Association has created a "Fixture Seal of Approval" for companies interested in certifying their bulbs and fixtures as dark-sky friendly. To qualify, fixtures need to be full cutoff.

In Las Cruces, NM, home of Lac Cruces Astronomical Observatory, all new outdoor lighting has been required to utilize full-cutoff designs since 2000, and existing outdoor lighting must be brought up to code by 2010.

Spotlight's on you

The challenge is getting people to invest in the issue and take action. Very few government entities have ordinances or regulations in place to help curb light pollution. And where regulations do exist, they often are not well-known and therefore not enforced. Often it is cities with astronomy observatories nearby that spearhead the efforts to turn down the glare and protect the rights of their citizens against light trespass.

Palomar Observatory, San Diego
On Palomar Mountain, where the Palomar Observatory is located, the unaided view of the night sky is limited because of light pollution from San Diego County. Photo courtesy of Scott Kardel

The San Diego area has some of the toughest ordinances on the books. Astronomers at Palomar are very active in raising awareness of light trespass. Being near large municipalities allows for plenty of outreach and education opportunities. Palomar is launching a program this fall where astronomers loan sky-brightness meters to local teachers.

"They can make measurements with their students and compare them to the sky brightness measured at Palomar and other sites that will be using the same instruments to monitor the sky," Kardel says. Palomar also has a new program in the works called One Star at a Time that encourages people to take control of their own lighting and take an active role in limiting light pollution.

Light pollution San Diego, CA
The glow from San Diego and the surrounding region in California is present almost every night around the 200-inch Hale Telescope at the Palomar Observatory. Photos courtesy of Scott Kardel.

"Most people are quite unaware that light pollution impacts more than just astronomers and that there is potentially a substantial amount of money that can be saved by using smarter lighting," Kardel says. "Getting people out under a sky with little or no light pollution can show them what the sky is supposed to look like."

The IDA has been very active in raising awareness, creating groups, and approaching governments. The organization has developed a set of model lighting ordinances, the IES/IDA Model Lighting Ordinance, to assist astronomers and governments. Still open to public comment and input, once IDA approves the final language in the model ordinance, "It will be the ideal template to use to work with local planners to create outdoor lighting standards in your community," says Bob Parks, IDA executive director.

Spread the word, not the light

The McDonald Observatory in Texas is also reaching out to communities to try and preserve their near-pristine dark-sky conditions. Wren and others at the observatory are involved in outreach programs, advocating with municipalities, and bringing students to the observatory to see the stars in action. The observatory also offers supplementary funding for municipalities interested in upgrading their lights.

Milky Way over McDonald Observatory
Light from the Milky Way illuminates the night sky above the Hobby-Eberly Telescope at the McDonald Observatory in Texas on a clear night with area light pollution minimized. Photo courtesy Frank Cianciolo/McDonald Observatory

Wren says when dealing with city governments, it's the money-saving potential that ends up catching people's interest. "When I talk to groups, I usually don't harp on the dark-sky issue. But when I start talking about how much money is being wasted on poorly designed light fixtures, they perk up," Wren says.

Parks and Wren both state that holding star parties and stargazing events are some of the most effective ways to raise awareness about light pollution. "People are amazed to see what they are missing," when they have a chance to look at the night sky through a telescope, Parks says. "You can then point to the acorn lights that are one of the worst light fixtures in existence as part of the problem. People then see the connection and really get it."

Education about light pollution is key. "Anything that can raise public awareness is useful," Kardel says.

Wren adds: "It's 90% public education. It's just the question of informing people and how it will benefit them."

Other organizations are reaching out to lawmakers and international organizations. The American Medical Association has passed a resolution demanding stricter light-pollution regulations and enforcement of light trespass codes already in place.

In New Zealand, representatives from the Lake Tekapo Starlight Reserve Working Party and the Department of Conservation attended a UNESCO World Heritage Committee meeting in August 2010 to request that the Lake Tekapo area become the first World Heritage Starlight Reserve. They argued that stars and planets are part of natural heritage, that the sky is a cultural resource, and that Lake Tekapo was one of the last on Earth that could be classified as having "pristine" night viewing. Astrotourism is an income source for the area.

Dangers of LEDs

LEDs seem like a good solution for outdoor lighting, since they are more energy efficient than many alternative light sources. But LEDs that include light from all wavelengths are closer to sunlight than traditional bulbs and are therefore more disruptive to many species.

"Such light sources are broadband in color, making it difficult or impossible to isolate individual spectral lines," Kardel says. "Further, many of these light sources have a large amount of blue light in their spectrum. Blue light disproportionately brightens the sky, by some 15-20%, so any of the blue portion of the spectrum from these lights will add more to sky glow than other colors."

Parks says glare from these fixtures will be perceived as more intense than other light sources like high-pressure sodium (HPS). "The broad-spectrum white light will have a profoundly negative effect on light scatter and sky glow. It is estimated that broad-spectrum white light will produce 200% more scatter and sky glow than a high-pressure sodium light source with equivalent lumen output," Parks says. "The higher blue light content of LED has the potential to interfere with circadian rhythms and cause sleep disorders."

Some LED manufacturers are designing their lights with light trespass in mind, and some have been certified dark-sky compliant.

Gerhard Eisenbeis, professor of biology and zoology at University of Mainz (Germany), found that different streetlights attract and kill vastly varying numbers of insects. The least disruptive were those using the "warm" variety of LEDs that emit less blue light.

"Much more research needs to be done on this issue before widespread adoption of LED lighting occurs," Parks concludes. Most astronomers advocate the use of low-pressure sodium lighting near observatories.

For now, simply raising awareness, asking people to turn their lights off, and leading by example are powerful acts that everyone can participate in and help aid the cause.

"Talk to people and governments. Be persistent," says Kardel. "Also, seek out help whenever you can get it. Amateur astronomers are passionate about the night sky and want to protect it. They can be of great help in getting the word out and educating people on the issues."

The International Dark-Sky Association regards any adverse effect of artificial light, including sky glow, glare, light trespass, light clutter, decreased visibility at night, and energy waste, as light pollution.

Warning lights only as needed

Radio towers, wind turbines, and other tall structures typically beam bright lights out for airplane safety, causing light trespass to anyone within sight of the towers. OCAS (Obstacle Collision Avoidance Systems), a company based in Norway, has developed what are essentially motion detectors for wind turbine towers. A low-power, ground-based radar will detect and track any aircraft's proximity to the tower and allow the tower's visual warning lights to remain at a low beam until an aircraft is detected.

You can participate

GLOBE at Night is an annual citizen-science campaign to encourage people all over the world to record the brightness of their night sky.

For two weeks every March, when the moon is not out during the early evening and the constellation of Orion can be seen everywhere, participants match the appearance of Orion with seven star maps of progressively fainter stars found on the website. They then submit their measurements online with their date, time, and location.

The dots (or points) on the resulting world map represent the contributed measurements of night sky brightness.

This year, the campaign received more than 17,800 measurements from 86 countries.

Read more in the SPIE Newsroom about the global campaign to save energy and fight light pollution.


Beth Kelley is a science and technology writer. 

Have a question or comment about this article? Write to us at spieprofessional@spie.org.

DOI: 10.1117/2.4201010.05

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