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Light Pollution

February 4, 2013

There's nothing like a week-long power failure to remind you of the importance of electrical lighting. Such a power failure is what my neighbors and I experienced after hurricane Sandy, although some had backup generators. Fortunately, we now have highly efficient white light-emitting diode flashlights for use in such emergencies. They're a big advance over incandescent bulb flashlights, which are surprisingly still being sold.

Unfortunately, as my last visit to The Home Depot confirmed, the prices for LED replacements for incandescent bulbs for general home lighting are still too high. The sales pitch is still that the money saved in "x" years on your electric bill and not having to buy replacement bulbs makes the LED lamps worthwhile. People are still too cautious in spending today's dollar on some potential future saving. There's always the chance that LED technology will be surpassed by research on triboluminescent squirrel fur.

One advantage of the hurricane Sandy power outage was my being able to sleep in a dark house without the distracting motor sounds of the refrigerator and circulating pump for the heating system. The novelty diminished after the second day of no heat, but it did remind me of all our indoor light pollution, which consists of digital clocks and other displays, and pinpoints of LED light everywhere.

Indoor light pollution can be detrimental to your mental health. A recent study by neuroscientists at the Ohio State University Wexner Medical Center demonstrated that chronic exposure to dim light at night leads to depression in hamsters.[1] Hamsters, when exposed to light at night over a four week period, displayed symptoms of depression. These symptoms, which also appeared as changes in the hamster brain, disappeared after a two weeks of a normal day-night cycle. If we can generalize this to humans, it might explain the growing rate of depression during our last five centuries.[1]

Because of my early interest in astronomy, I've been aware of the growth of outdoor light pollution for quite some time. Light pollution is one reason why observatories are located in remote locations. Long gone are the days when astronomers could do all their observations at convenient locations, such as the Palomar Observatory. At most observatories, optical filters are needed to reduce light pollution. The worst offenders are sodium-vapor and mercury-vapor street lights.

Earth night lights

This NASA satellite image of the Earth at night was compiled from hundreds of low moonlight images taken from October 1994 - March 1995. Only cloud-free images were used. (NASA/Goddard Space Flight Center image, via Wikimedia Commons. Click for a larger image.)

Paul Bogard, a professor of English at James Madison University, has written an opinion piece on light pollution for the Los Angeles Times.[2] This article has been syndicated to many other media sites.[3] Bogard is the author of the forthcoming book, "The End of Night: Searching for Natural Darkness in an Age of Artificial Light," scheduled for release by Little, Brown and Company, July 9, 2013.[4]

Bogard writes about light pollution of the night sky, but from a personal perspective. Having experienced a truly dark sky in childhood at his family cabin on a Minnesota lake, he bemoans the fact that 80% of today's children in the United States will never see the Milky Way.[2] He then recounts other reasons why we should strive for a darker night.

The human body needs darkness to produce melatonin, a hormone that keeps certain cancers from developing. The World Health Organization has classified night shift work as a probable cause of cancer. Lack of darkness causes sleep disorders; and persistently restless sleep has been linked to many diseases, including depression, as mentioned above. Lest we be overly anthropocentric, the wildlife around us are affected as well.[2]

According to Bogard, sky illumination at night has been increasing at about six percent per year in the United States and Western Europe.[2] Mitigation of light pollution would also lead to an energy-savings. Street lights would be more efficient if they illuminated more of the street, and less of the sky. I'm often upset at the wasted energy of shopping center parking lots illuminated through the night when none of the shops are open, possibly because someone forget to throw a switch, or a timer is broken.

North Korea satellite night image

There's a correlation between a country's night illumination and its economic development.

This image shows Japan, South Korea, and a very dark North Korea. The motto of North Korea is "Powerful and Prosperous Nation."

(Detail of a NASA/Goddard Space Flight Center image, via Wikimedia Commons.)

LED street lighting and diminished public lighting after midnight are among the mitigation strategies mentioned in Bogard's article. Bogard is not a scientist, so his article waxes philosophical about the solitude, quiet and stillness that accompany darkness. He mentions Van Gogh's "The Starry Night."[2] In the truly dark skies of our ancestors, the Milky Way was prominent enough to cast a shadow.

We can extend the concept of light pollution to other parts of the electromagnetic spectrum, especially to the idea of radio spectrum pollution. The World Radiocommunication Conference, formerly the World Administrative Radio Conference, is an international collaboration to harmonize the assignment of the radio spectrum. It's organized by the International Telecommunication Union, and its last meeting was held January 23 - February 17, 2012.

Radio astronomers have a stake in radio frequency allocation around certain important wavelengths, such as the 21 cm line of hydrogen at 1420.40575 MHz (see figure). This frequency is shared with two sources of supposedly non-interfering radio sources; namely, Earth exploration satellites, and space research.

Figure caption

Congestion at the Water Hole. The Water Hole is the region of the electromagnetic spectrum that includes the 21 cm line of hydrogen (1420.40575 MHz). The unlabeled green area is assigned to broadcast satellites. (Illustration by the author, rendered using Inkscape, from frequency allocation data.)

What's important to realize is that such frequency allocations are for "intentional radiators." Malfunctioning or poorly designed transmitters will radiate harmonic and intermodulation signals into other bands. Digital electronic devices such as computers and television receivers, which are not transmitters, can still radiate radio frequency interference.

Just a decade ago, households may have had just a single transmitter, such as a cordless telephone. Today, an average household might contain more than a dozen transmitters, including cellphones and Wi-Fi devices. Alas, where radio communication is concerned, it's a jungle out there.


  1. T A Bedrosian, Z M Weil and R J Nelson, "Chronic dim light at night provokes reversible depression-like phenotype: possible role for TNF," Molecular Psychiatry, July 24, 2012, doi: 10.1038/mp.2012.96.
  2. Paul Bogard, "Let there be dark," LA Times, December 21, 2012.
  3. Paul Bogard, "Let there be dark: Light pollution is changing the way life works," Pittsburgh Post Gazette, January 6, 2013.
  4. Paul Bogard, "The End of Night: Searching for Natural Darkness in an Age of Artificial Light," Little, Brown and Company, July 9, 2013, ISBN-13: 978-0316182904 (Hardcover, 304 pages, via Amazon).
  5. United States Frequency Allocations Chart 2011 (PDF File, via Wikimedia Commons).

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