The night sky in the country looks remarkably different than the sky view near a city. More stars are visible and brighter, and in some remote areas, the Milky Way galaxy extends across the sky from east to west. In contrast, lights in the city illuminate night skies, hiding many of the stars. Outdoor lighting that interferes with the natural landscape is called light pollution. As urban areas grow, so does this type of pollution. Learn about the impact of light pollution and follow through with ways to reduce excess lighting in your neighborhood.
Light pollution occurs when artificial light intrudes on the nighttime setting. This phenomenon is pronounced around urban centers, where city lights diminish the view of stars and planets. A satellite view at night shows light pollution as glowing regions around urban areas. In addition to brightened skies around cities, light pollution also refers to any outdoor light that creates glare and interferes with the natural night environment. The National Park Service refers to a single source of light that intrudes on the night as "light trespass." (See References 3)
Light pollution results from outdoor lights aimed upward or sideways --- the light scatters in the atmosphere and reflects back to the ground. The result is sky glow. Particles in the atmosphere responsible for air pollution accentuate light pollution by increasing the amount of light scatter. According to the International Dark-Sky Association, light sources that emit blue light are particularly disruptive to night skies due to greater light scattering. (See References 2 and 3)
According to the National Park Service, city lights as far as 200 miles away diminish views of night skies. Light pollution is a major concern for observatories as lights from urban areas compete with lights from stars and planets, reducing visibility of the objects that observatories study. This type of pollution also affects wildlife and plants. Night lights disorient hatching sea turtles, migrating birds and nocturnal animals. Lights attract insects, which may in turn interfere with pollination of nocturnal flowers. (See References 3 and 4) In humans, light pollution can interfere with natural circadian rhythms by preventing the production of melatonin, the chemical that regulates sleep patterns. Low melatonin levels have been linked to increased cancer risks. (See References 1)
There are ways to reduce light pollution, starting in your own neighborhood. Make sure outdoor lights reflect downward in what are called fully-shielded fixtures. Also consider exchanging high-wattage bulbs for dimmer ones and selecting warm-white lights with low emission of blue light. A great way to save energy and reduce trespassing light is to turn off outdoor lights unless needed. (See References 1, 2 and 3)
- International Dark-Sky Association; Seeing Blue; 2010
- Caltech Astronomy: Light Pollution and the Palomar Observatory
- National Park Service; Natural Lightscapes Overview; 2007
- Astronomical Society of the Pacific; A Silent Cry for Dark Skies; Connie Walker; 2008
- CNN SciTech Blog; The Brightest Spots on Earth; Peter Dykstra; April 2008
First published in 2001, Marie Lenahan writes about horticulture, food and green living. Her work has appeared in gardening magazines and academic journals. Lenahan holds a Ph.D. in horticultural science.
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