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Artificial Light Impacts Astronomy as Well as Human Health, the Environment, and World Views, Experts Say

The pervasive use of artificial lighting not only has fogged the view of astronomers seeking to study the stars, it also has been linked to human health problems, environmental disruptions and fundamental questions about the impact of a disappearing night sky on the intellectual and spiritual curiosity of future generations.

With two-thirds of humanity now living under light-polluted skies, the implications for global health and well-being were discussed by panelists at 10 May screening of The City Dark: A Search for Night on a Planet that Never Sleeps, co-sponsored by the American Astronomical Society and the AAAS Dialogue on Science, Ethics and Religion.

Scientists have linked artificial light with various human health problems, from sleeplessness to depression, as well as environmental consequences, including the death of migrating birds and sea turtles confused by urban glow. But artificial light also can have a psychological and spiritual impact, according to panelists at the screening and experts interviewed in the film.

Debra Elmegreen, president of the American Astronomical Society, said she is concerned that the reduced visibility of the night sky limits human interaction with nature and may also be curbing some of the childhood wonder and curiosity that produces future astronomers.

Increasingly, urban youth only see constellations on computer screens or in planetariums, said Jennifer Wiseman, director of the AAAS Dialogue on Science, Ethics and Religion, which hosted the film screening and panel discussion. The lack of the night sky may therefore affect their sense of the scale of the universe and their place in it, she noted.

“Looking at all the stars in the cosmos achieves a resetting of your ego,” Hayden Planetarium astrophysicist Neil deGrasse Tyson said in the film, which is a production of Wicked Delicate Films, written, directed and produced by Ian Cheney.

Tyson said, in fact, that he didn’t see the night sky, growing up in the Skyview Apartments of the Bronx, until he visited a planetarium at age 9. “The stars came out and I thought it was a hoax,” he said. In contrast, Wiseman recalled taking long evening walks in rural Arkansas as a youngster, instantly putting her eighth-grade problems into a broader perspective as she viewed the myriad stars from horizon to horizon.

Before industrialization, the film noted, navigation was based on the positions of the stars. Later, whale-oil lamps were replaced by gas lights, and in 1879, the incandescent light bulb was successfully demonstrated. The first hydroelectric power plant opened three years later, and early versions of the light bulb soon gave way to brighter and brighter technologies ultimately leading to the modern phenomenon of urban sky glow.

Cheney’s film explains that light pollution is caused by upward-shining light that bounces off dust and particulates in the air. Much of this illumination is unnecessary: One source in The City Dark estimated that as much as half of the $1.5 billion worth of electrical light generated in the United States every year may be wasted light.

With so much stray light illuminating the atmosphere and communication technologies utilizing radio band passes, astronomers struggle to find skies that are dark enough and free of electromagnetic noise to allow for quality scientific research.

Excessive light exposure has also been linked with health impacts ranging from changes in circadian rhythms and sleep patterns, to depression and weight gain, to the development of cancerous tumors, said Charles A. Czeisler, director of the division of sleep medicine at the Harvard Medical School. Czeisler was one of four experts on hand for the AAAS screening.

“Electric light has a much more profound effect on our health than we might otherwise realize,” said Czeisler. His research has shown, for example, that people without sight can retain normal circadian rhythms if they have certain retinal ganglion cells that contain melanopsin, a photopigment that conveys sensitivity to light. People with blindness who do not have these cells cannot reset their wake-sleep “clocks,” and thus may feel as though they are in a perpetual state of jet lag.

An expert interviewed for The City Dark, cancer epidemiologist Richard G. Stevens with the University of Connecticut Health Center, said women who work night shifts have a greater risk for developing breast cancer. David Blask of Tulane University said that blood rich in the sleep hormone melatonin can suppress the formation of cancerous tumors in rats.

Czeisler noted that human melatonin production rapidly declines in response to light exposure, yet most city dwellers awaken early for work or school, spend long days under artificial light, often consuming caffeine, then stare at computer and television screens at night. He describes the impacts of this lifestyle on melatonin production as “The Big Squeeze.”

The film also highlighted some of the environmental consequences of increased artificial light. The decline of fireflies, the death of birds that collide with brightly lit buildings during migration, and the fatal disorientation of newly hatched sea turtles are only a few examples of how light pollution affects different species, experts said.

How does the loss of an authentic night sky affect people’s views of the world, or even their spiritual beliefs? Astronomer Jeff Kuhn at the University of Hawaii commented, “Seeing the universe around us tells us about our own part of the universe. And to close that door I think would change the character of humankind entirely.” Panelist Robert Morrison, associate professor of religion at Bowdoin College, noted that many civilizations throughout history have used the night sky as a way to interpret the world and the passage of time. Yet, young people living in big cities can only see a handful of stars on any given evening.

Two other panelists, Elmegreen and Chad Moore of the National Park Service, manager of the Night Skies program, suggested practical steps people can take to help address light pollution and wasted light. Moore recommended, for example, placing light only where it is needed, and then using it only as needed. Shielded lighting, designed to point downward, is essential. Moore also urged the use of high-efficiency white or amber lights (not blue, since blue light inhibits the body’s melatonin production).

The City Dark featured architectural choices such as under-story lighting that can help to reduce light pollution in cities. The film also noted that some municipalities are looking at lighting ordinances as a way to minimize excessive artificial light.

Elmegreen urged the AAAS audience to eliminate diffuse lighting, and she added that low-pressure sodium lights are a good choice. She also suggested talking with neighbors about the importance of lighting choices, and joining star-gazing clubs. “Keep looking up,” Elmegreen said, in closing.


The following tips have been adapted from the National Park Service Night Skies Web site and remarks by Chad Moore, manager of the program.

  • Enjoy the Night

People protect what they cherish.

  • Use Light Only When You Need It

Use motion sensors to turn lights on and off, as needed. Use timers for lights, too.

  • Shield Your Lights

Lights should point downward, not everywhere. Full cut-off light fixtures are now available. Existing lights can also be adjusted to point downward or retrofitted with simple metal shrouds.

  • Use Less Light

An efficient, shielded light fixture can use a smaller wattage bulb and still be effective. Even a 25- or 40-watt incandescent bulb, or a 9-watt compact fluorescent, is enough to light a porch or driveway. Choose white or amber (not blue) lights.

  • Talk to Your Neighbors

Encourage everyone to help bring back the night sky.


Learn more about the film, The City Dark: A Search for Night on a Planet that Never Sleeps.

Learn more about the AAAS Dialogue on Science, Ethics and Religion.

What can you do to preserve the night sky?