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 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.
 |
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 |
