Did You Know...
A list of quick facts about light.
It is estimated that at least 100 million birds are killed annually due to collisions with manmade structures, which include wind turbines, power lines, glass and towers. Collisions due to urban light represent approximately one third of all collisions, while two thirds of collisions occur during the daytime. 90,000 birds are killed flying into buildings in New York City alone. (American Bird Conservancy)
The lights of Las Vegas, Nevada, are visible from eight different national parks and are the dominant cause of light pollution in Death Valley National Park, 93 miles from the city. (Science News Online)
According to Energy Star, a U.S. Environmental Protection Agency and U.S. Department of Energy program, replacing a single incandescent bulb with a compact fluorescent light (CFL) bulb in every U.S. household would be the environmental equivalent of taking 800,000 cars off the road. (Energy Star)
About 63 percent of the world's population and 99 percent of the population in the European Union and United States (excluding Alaska and Hawaii) live in areas where the night sky is above the threshold set for polluted status. (Chepesuik, Ron. "Missing the Dark: Health Effects of Light Pollution." Environmental Health Perspectives, January 2009.)
The Phoebus cartel (1924-1939) was formed by light bulb manufacturers Osram, Philips, Tungsram and General Electric, among others. Manufacturers in the cartel not only fixed prices so that no manufacturer had to fear the competition of the others, but also secretly signed a commitment, pledging each other that light bulbs would be designed and constructed such that their expected life time would not exceed 1000 hours. (Glaubitz, John Paul Adrian, "Modern Consumerism and the Waste Problem.")
Glass building typology is responsible for the majority of bird deaths, two thirds of which occur in the daytime. The U.S. Green Building Council recently issued a new pilot project under the Leadership in Environment and Energy Design (LEED) program to reduce bird collisions with buildings that focuses on alterations to building materials, such as glazing. (U.S. Green Building Council)
Worldwide, 1.6 billion people do not have access to electricity (UNESCO. "Global Climate Change.")
LEED provides building owners and operators with a framework for identifying and implementing practical and measurable green buildings and reducing light pollution and light trespass. Nearly 9 billion square feet of building space participate in the LEED rating systems and 1.6 million feet are certified daily around the world.
(U.S. Green Building Council.)
Light Pollution Basics
The International Dark-Sky Association (IDA) describes light pollution as any adverse effect of artificial light.
Established in 1988, the IDA was the first organization to call attention to the hazards of light pollution and it is dedicated to protecting and preserving the nighttime environment through quality outdoor lighting. The IDA promotes one simple idea: Light what you need, when you need it.
The IDA defines the four components of light pollution as:
Urban Sky Glow: the brightening of the night sky over inhabited areas
Light trespass: light falling where it is not intended, wanted or needed
Glare: excessive brightness that causes visual discomfort (high levels of glare can decrease visibility)
Clutter: bright, confusing and excessive groupings of light sources, commonly found in over-lit urban areas; the proliferation of clutter contributes to urban sky glow, trespass and glare
The Growth of Artificial Light
Though light at night has brought indisputable benefits, its excessive and unregulated use has been problematic.
In 2007, the United Nations estimated that for the first time in history the world had a predominantly urban population: 51 percent urban versus 49 percent rural.
Light pollution is a direct outgrowth of industrialization. While at least 2,500 individual stars should be visible in an unpolluted night sky, in a typical suburb only 200 to 300 stars are visible, and in a city, that number is often fewer than a dozen. According to astronomer Andrew Fraknoi, it is estimated that as many as 80 percent of people in the world have never seen the Milky Way.
In the film The City Dark, filmmaker Ian Cheney describes light pollution as light reflecting off moisture and dust in the air, creating a glow in the sky. The most common cause of light pollution is over-illumination — streetlights and outdoor security lights that spill outward, billboard and landscape lights directed upward and businesses like convenience stores and gas stations operating with excessive light output. Though light at night has brought indisputable benefits, its excessive and unregulated use has been problematic. According to the Institute for Local Self-Reliance, each night almost one third of the light used outdoors escapes into the night sky, where, rather than providing useful illumination, it causes glare, sky glow and other types of light pollution. According to estimates from the International Dark-Sky Association, each year in the United States more than $1 billion dollars are spent to generate this wasted light.
While there has been no global-scale data on the distribution and magnitude of artificial sky brightness ("ecology of the night" is a fairly recent area of study), many amateur astronomers use the Bortle Dark-Sky Scale to rate the night sky. The scale ranges from class 1 — the darkest skies — to class 9 — skies typical of the inner city. Class 1 skies can be found in places like remote areas of Chile, Antarctica or the Australian outback. According to a comprehensive study of night sky quality conducted by the U.S. National Park Service, the Natural Bridges National Monument in southeastern Utah is the only Bortle class 2 location in the United States. New York City rates as class 9.
According to Jane Brox (the author of Brilliant: The Evolution of Artificial Light), the brightest spots on the map correspond to prosperity and urbanization rather than population density. The National Bureau of Economic Research released a report in 2011 proposing satellite images be created of light at night and used as an indicator for measuring GDP growth. As of 2012, both Western Europe and the Eastern seaboard of the United States are brighter than any place in China or India.
To find the darkest skies near you, visit the International Dark-Sky Association (IDA) at http://www.darksky.org/ and access the Dark Sky Finder or the Clear Sky Chart, which shows sky conditions over the following 48 hours for specific observation sites in North America (over 3,500 currently listed).
Photo caption: Lighting store owner Larry Birnbaum shows off his collection of antique and modern lighting. Credit: Wicked Delicate Films LLC.
Sources:
» Berg, Nate. "Darker Cities, Brighter Stars." The Atlantic, December 1, 2011.
» Bower, Joe. "The Dark Side of Light." Audubon, 2000.
» Brox, Jane. Brilliant: The Evolution of Artificial Light. New York: Houghton Mifflin, 2010.
» Cinzano, P. et al. "The First World Atlas of the Artificial Night Sky Brightness." Monthly Notices of the Royal Astronomical Society, Vol. 328 (2001).
» Friends of the Columbia Highlands.
» Great Basin National Park.
» Harder, Ben. "Light All Night." Science News, May 7, 2006.
» Henderson, Vernon J. et al. "Measuring Economic Growth from Outer Space." The National Bureau of Economic Research, 2011.
» Institute for Local Self-Reliance.
» International Dark-Sky Association.
» Moore, Chadwick A. "Visual Estimations of Night Sky Brightness." The George Wright FORUM, Vol. 18 (2001).
» NASA. "Visible Earth."
» National Park Service. "Natural Bridges."
» PBS. "Seeing in the Dark."
Effects of Light on Astronomy
Irving Robbins, a Brooklyn-born astronomer running the last remaining observatory on Staten Island, New York, is a reminder that stars could once be studied in New York City. Now only the brightest objects shine through the light-polluted sky. Robbins says, "I've seen the Milky Way twice — when there were blackouts."
The City Dark introduces Irving Robbins, a Brooklyn-born astronomer running the last remaining observatory on Staten Island, New York. He is a reminder that stars could once be studied in New York City. Now only the brightest objects shine through the light-polluted sky. Robbins says, "I've seen the Milky Way twice — when there were blackouts."
Filmmaker Ian Cheney leaves New York City seeking darker skies and finds his way to Sky Village, a dark-sky haven for astronomers in rural Arizona. The village's denizens come from all walks of life. What draws them together is their need to be close to a dark night sky. Cheney visits a mountaintop in Mauna Kea, Hawaii, considered the best site for professional astronomy in the world. Here, astronomers rely on Pan-STARRS, the world's newest, largest telescope-camera, to detect Earth-killing asteroids, but urban growth in the valley below creates a luminous haze that impedes their work. "It's as though you're looking through fog," says John Tonry of the University of Hawaii.
Beyond the problems of decreased visibility due to urban sky glow, light trespass, glare and clutter, astronomers face another problem caused by light pollution. Not only is the night sky harder to see, but the objects astronomers can see are more difficult to analyze. Astronomers analyze the physical properties that make up stars, galaxies and other objects in the sky through spectroscopy. Spectroscopy is the analysis of the color components of light of an object. For astronomers, this means creating a spectrogram showing the optical spectrum of a given galaxy. The spectrogram allows the astronomer to use these color components of light to figure out the chemical properties and temperatures of the objects they are observing and make determinations about how fast the objects are moving. Spectroscopy has long been considered the most valuable tool in the astronomer's toolbox. As telescopes become larger and more sensitive to refracted light, there is an increasing need for observation in light controlled environments.
Some of the best locations for conducting telescopic observation are high and dry places, such as the Atacama Desert in Chile or the South Pole. Dry locations at high altitudes allow for the least sky noise, or background atmospheric interference caused by atmospheric pollution, humidity and light. Astronomers have been stationed in these remote locations for more than 50 years, but as more and more astronomers leave behind less useful stations and flock to these, many once populated stations are out of commission.
Photo caption: Dark sky reserves, like this one around Mont Megantic in Canada, preserve starry night skies for researchers and amateur stargazers alike. Credit: Wicked Delicate Films LLC.
Sources:
» Cornell University. "Ask an Astronomer: How Does Light Pollution Affect Astronomers?"
» Fischer, David E. "Going to the Ends of the Earth." Astronomical Society of the Pacific, No. 38, Spring 1997.
» University of Arizona. "What is Spectroscopy?"
» Wright, Gregory. "Astronomy at the South Pole." Optics and Photonics News, Optical Society of America, January 2004.
Effects of Light on Ecology
The City Dark explains that astronomers are not the only ones losing the night. Biologists along the Florida coast trace the death of thousands of hatching sea turtles to their disorientation by coastal lights. Volunteers at the Field Museum in Chicago collect from city sidewalks thousands of dead birds, about one-third of which are victims of light-induced disorientation and collisions into lit buildings.
As Chad Moore of the National Park Service explains, "When we add light to the environment it has the potential to disrupt habitat, just like running a bulldozer over the landscape can."
While our understanding of the full spectrum of ecological consequences of light pollution is limited, we do know that artificial light at night contributes to disruption of natural behaviors. Some less recognized implications include the interruption of reproduction, foraging and inter-species communication. These are all light-sensitive cycles that are disrupted during unexpected periods of attraction to or repulsion from artificial light sources. For example, sockeye salmon fry stop swimming downstream when exposed to any light above 0.1 lux (the standard of measurement for lighting) and often end up in low-velocity waters near shore, which brings them into close contact with predators. Researchers believe this phenomenon explains the recent decline in the sockeye salmon population in Cedar River, Washington, a location that is exposed to both direct light and sky glow.
Many species of slow-flying bats, such as the horseshoe bat, have increasing difficulty procuring food. Bats are genetically predisposed to avoid light, and now that the hours of darkness are limited, they don't have as much time to seek out food. Also, bats eat insects, which tend to swarm around lights, so fewer are left to be caught in the dark. Other species are affected, too. For example, when days were extended to 16 hours due to artificial light, white-tailed bucks began feeding two weeks earlier than usual and weighed 20 pounds more than previously at winter's end.
Territorial singing in birds is also changing. While northern mockingbirds have evolved to sing only shortly before sunrise during mating season, they have recently been observed singing at night in artificially lit areas. When exposed to high levels of artificial light, American robins will often initiate their morning songs earlier, sometimes up to 100 minutes before the onset of dawn. According to Wildlands CPR's quarterly journal, prolonged singing could result in higher energy demands, greater predation risk and earlier yearly feeding times. These changes may become serious for threatened and endangered species.
As awareness of the danger of artificial light to sea turtles grow, an increasing number of communities are restricting coastal illumination. Countries all over the world have passed ordinances that control the amount and type of light used in coastal environments. As the list grows, hatchling sea turtles are starting to be able to find the sea without the help of human volunteers to guide them. Learn more about local and regional action by visiting www.seaturtle.org. (International Dark Sky Association)
Photo caption: Millions of birds collide with buildings each year. Credit: Wicked Delicate Films LLC.
Sources:
» Coastal Carolina University. "Does Light Intensity Influence Song Output by Northern Mockingbirds?"
» Ecological Consequences of Artificial Night Lighting, ed. by Catherine Rich and Travis Longcore. Washington, D.C.: Island Press, 2005.
» International Dark-Sky Association
» "Street Lights Pushing Slow Bats Towards Extinction." The Telegraph, June 19, 2009.
» University of British Columbia. "Light Pollution: Environmental Effects of Roadway Lighting."
» Wildlands CPR. "Effects of Artificial Lighting on Wildlife."
Effects of Light on Human Health
In The City Dark, epidemiologist Richard Stevens of the University of Connecticut suggests a link between light at night and breast cancer.
In The City Dark, epidemiologist Richard Stevens of the University of Connecticut suggests a link between light at night and breast cancer. In 1987, Stevens wrote in the American Journal of Epidemiology that "the use of electric lighting, resulting in lighted nights, may produce circadian disruption," which causes changes in hormone levels in the body.
Human beings (and nearly all living things) have evolved under a natural rhythm of day and night. The 24-hour cycle during which the body goes through physiological changes is called a "circadian rhythm," or colloquially the "internal body clock."
Circadian rhythms respond significantly to light and darkness. In fact, melatonin is often called the "hormone of darkness" because it is secreted in the dark and it is believed to play an important role in fighting off cancer. If bodies are consistently exposed to artificial light at night, or LAN — whether from streetlights or a television glare — melatonin hormone production can be disrupted.
Stevens' LAN research has included studies indicating that night-shift workers are almost twice as likely to develop breast cancer as day-shift workers, and the World Health Organization has classified shift work as a probable cause and risk factor for cancer. Although the research linking LAN to increased risk of cancers is still hypothetical, many chronobiologists suggest limiting one's prolonged exposure to bright lights during nighttime hours.
According to the National Institutes of Health, a change in a person's internal body clock impairs his or her ability to sleep and wake at appropriate times and leads to a decrease in cognitive and motor skills. Disruption of these rhythms can contribute to insomnia, depression and cardiovascular disease. However, the Lighting Research Center emphasizes that stimulation of the human circadian system at night is not necessarily a health risk and that the type of light is a major factor, as are the intensity and the duration of light exposure of the retina.
On June 15, 2009, the American Medical Association voted unanimously to adopt resolutions to reduce light pollution and glare, advocating for use of energy efficient, fully shielded outdoor lighting.
Photo caption: Light pollution in a NYC bedroom. Credit: Wicked Delicate Films LLC.
Sources:
» International Dark-Sky Association. "Light Pollution and Human Health."
» Tala, Angelina. "Lack of Sleep, Light at Night Can Raise Cancer Risk." Medical Daily, October 11, 2011.
Light and Crime
While there is strong indication that an increase in lighting decreases the fear of crime, there are mixed opinions regarding a direct correlation between light and crime, and the evidence is inconclusive.
In The City Dark, historian Roger Ekirch states that humans have long feared the dark, and that crime was the original impetus for widespread street lighting on the planet.
While there is strong indication that an increase in lighting decreases the fear of crime, there are mixed opinions regarding a direct correlation between light and crime, and the evidence is inconclusive.
A recent New York Times article on the rise of crime in Oakland, California states that research has long shown a correlation between street lighting and crime. Brandon Welsh, a criminology professor at Northeastern University, says that streetlights act as "natural surveillance" and may reduce crime by 20 percent. In a review of the effects of improved street lighting on crime, Welsh and co-author David P. Farrington explain the recorded impact (that crime fell both at night and during the day) and conclude that lighting increases community pride and confidence and strengthens informal social control. The City Dark shows residents in Newark, New Jersey, agreeing that the introduction of bright new lampposts have made the community more livable and sociable.
However, some research indicates that an increase in number and brightness of streetlights actually increases the occurrence of crime, noting that street lighting allows perpetrators to monitor their own actions without the use of flashlights or other lighting devices that would make them visible to others. A case has also been made that offenders need lighting to detect potential targets and low-risk situations. In 1996, the National Institute of Justice published an assessment of crime and violence and considered the case of lighting outside ATM machines. The report posited that while an ATM user might feel safer when the ATM and its immediate surrounding area are well lit, this same lighting may make the patron more visible to passing offenders. A report from 2000, written by the Illinois Criminal Justice Information Authority, presented the effect of increased lighting levels in Chicago alleyways. In a one-year analysis after the upgrading and installation of brighter lights, the group cited an increase of 21 percent in reported offenses. Index offenses increased 14 percent (from 119 to 136), property offenses increased 20 percent (from 30 to 36) and non-index offenses increased 24 percent (from 279 to 347).
Most criminologists agree that crime is more complicated than light versus dark. Local factors can often determine whether a particular lighting strategy will be effective in deterring crime or not, and research is ongoing as more and more communities debate the merits of dark-sky friendly lighting.
Photo caption: Filmmaker Ian Cheney under a typical high pressure sodium streetlight in New York City. Credit: Wicked Delicate Films LLC.
Sources:
» Dark Sky Diary. "Do Brighter Street Lights Make You Safer From Crime?"
» National Criminal Justice Reference Service. "Street Lighting Projects "