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Artificial Light
Artificial Light | Zooplankton & Vertical Migration | Experiments

Artificial Night Lighting (ANL)

Nocturnal outdoor lighting cast by street lamps, advertising signs, flood-lit malls, and high-powered security lights has increased dramatically in both intensity and spatial coverage since the 1960’s due to urban sprawl and the use of brighter lights. ‘City lights’ according to analyses of satellite images now illuminate 2.7% of the surface area of the United States, an area equivalent to the state of Minnesota. This type of light, hereafter referred to as ANL (Artificial Night Lighting), also illuminates a vast array of aquatic habitats in both urban and rural areas. Major cities and their lights often flank or surround lakes (e.g., Lake Michigan, Chicago), rivers (e.g., Charles River, Boston and suburbs), and coastal areas (e.g., Long Island Sound, New York City). Importantly, however, ANL is not restricted to urban aquatic habitats. The nearshore area (i.e., littoral zone) of lakes, streams, and wetlands in rural areas is also vulnerable. This occurs, because security lights associated with waterfront property or vacation homes often illuminate portions of rural shorelines.

Satellite Image of World at Night

Satellite image of the world at night.

Photo courtesy of C. Mayhew & R. Simmon (NASA/GSFC), NOAA/NGDC, DMSP Digital Archive.

Two different components - glare and sky glow - comprise ANL, and their relative intensities in urban and rural areas will differ. Glare is direct light shining from a fixture into the eye of an observer or an organism, whereas sky glow refers to the composite illumination of the nighttime sky by city lights. Sky glow results from lights lacking fixture shielding causing them to cast light upward above the target area. When this light is reflected back to earth, it creates an aura of light above metropolitan regions that can sometimes be viewed more than 160 km from the city center. Hence, sky glow is associated with major cities, whereas glare can occur in both urban and rural areas.

Measuring Light

My students and I are quantifying ANL above and below water using a spectrometer. Our preliminary measurements of ANL (i.e., predominantly sky glow) in the Boston area reveal that:

1) wavelengths striking the surface of urban and suburban lakes are dominated by yellow light, and these wavelengths match those emitted from the most common street lamp in the U.S.A.

Black Histogram

Colored lines represent our measurements of ANL striking the surface of four lakes in the Boston Area. These wavelengths match those emitted from the most common street lamp in the U.S.A.
(Black histogram).

2) relative intensity of ANL at the surface of lakes along a suburban to urban gradient increased 3 to 6 fold; and

3) cloud cover increased the intensity of ANL by a factor of three to four (Moore et al. 2004).

In 2004, we are quantifying the absolute intensity of ANL and estimating its depth of penetration underwater.


Artificial Light | Zooplankton & Vertical Migration | Experiments

Image in header from © T. Credner & S. Kohle, AlltheSky.com


Created By: Bing Li '05 and Zsuzsa Moricz '06
Maintained By: Marianne Moore
Date Created: July 6, 2004
Last Modified: August 4, 2004
Expires: June 1, 2005