The American Medical Association (AMA) has just adopted an official policy statement about street lighting: cool it and dim it.
The
statement, adopted unanimously at the AMA's annual meeting in Chicago
on June 14, comes in response to the rise of new LED street lighting
sweeping the country. An AMA committee issued guidelines on how
communities can choose LED streetlights to "minimize potential harmful
human health and environmental effects."
Municipalities
are replacing existing streetlights with efficient and long-lasting
LEDs to save money on energy and maintenance. Although the streetlights
are delivering these benefits, the AMA's stance reflects how important
proper design of new technologies is and the close connection between
light and human health.
The AMA's
statement recommends that outdoor lighting at night, particularly street
lighting, should have a color temperature of no greater than 3000
Kelvin (K). Color temperature
(CT) is a measure of the spectral content of light from a source; how
much blue, green, yellow and red there is in it. A higher CT rating
generally means greater blue content, and the whiter the light appears.
A
white LED at CT 4000K or 5000K contains a high level of
short-wavelength blue light; this has been the choice for a number of
cities that have recently retrofitted their street lighting such as
Seattle and New York.
But
in the wake of these installations have been complaints about the
harshness of these lights. An extreme example is the city of Davis,
California, where the residents demanded a complete replacement of these high color temperature LED street lights.
Can communities have more efficient lighting without causing health and safety problems?
Two problems with LED street lighting
An
incandescent bulb has a color temperature of 2400K, which means it
contains far less blue and far more yellow and red wavelengths. Before
electric light, we burned wood and candles at night; this artificial
light has a CT of about 1800K, quite yellow/red and almost no blue. What
we have now is very different.
The
new "white" LED street lighting which is rapidly being retrofitted in
cities throughout the country has two problems, according to the AMA.
The first is discomfort and glare. Because LED light is so concentrated
and has high blue content, it can cause severe glare, resulting in
pupillary constriction in the eyes. Blue light scatters more in the
human eye than the longer wavelengths of yellow and red, and sufficient
levels can damage the retina. This can cause problems seeing clearly for safe driving or walking at night.
You
can sense this easily if you look directly into one of the control
lights on your new washing machine or other appliance: it is very
difficult to do because it hurts. Street lighting can have this same
effect, especially if its blue content is high and there is not
appropriate shielding.
The other issue addressed by the AMA statement is the impact on human circadian rhythmicity.
Color
temperature reliably predicts spectral content of light -- that is, how
much of each wavelength is present. It's designed specifically for
light that comes off the tungsten filament of an incandescent bulb.
However, the CT rating does not reliably measure color from fluorescent and LED lights.
Another
system for measuring light color for these sources is called correlated
color temperature (CCT). It adjusts the spectral content of the light
source to the color sensitivity of human vision. Using this rating, two
different 3000K light sources could have fairly large differences in
blue light content.
Therefore, the
AMA's recommendation for CCT below 3000K is not quite enough to be sure
that blue light is minimized. The actual spectral irradiance of the LED
-- the relative amounts of each of the colors produced -- should be
considered, as well.
The reason lighting matters
The
AMA policy statement is particularly timely because the new World Atlas
of Artificial Night Sky Brightness just appeared last week, and street
lighting is an important component of light pollution. According to the
AMA statement, one of the considerations of lighting the night is its
impact on human health.
In previous articles for The Conversation, I have described how lighting affects our normal circadian physiology, how this could lead to some serious health consequences and most recently how lighting the night affects sleep.
In the case of white LED light, it is estimated to be five times more effective at suppressing melatonin
at night than the high pressure sodium lamps (given the same light
output) which have been the mainstay of street lighting for decades.
Melatonin suppression is a marker of circadian disruption, which
includes disrupted sleep.
Bright electric lighting can also adversely affect wildlife by, for example, disturbing migratory patterns of birds and some aquatic animals which nest on shore.
Street lighting and human health
The AMA has made three recommendations in its new policy statement:
First,
the AMA supports a "proper conversion to community based Light Emitting
Diode (LED) lighting, which reduces energy consumption and decreases
the use of fossil fuels."
Second,
the AMA "encourage[s] minimizing and controlling blue-rich environmental
lighting by using the lowest emission of blue light possible to reduce
glare."
Third,
the AMA "encourage[s] the use of 3000K or lower lighting for outdoor
installations such as roadways. All LED lighting should be properly
shielded to minimize glare and detrimental human and environmental
effects, and consideration should be given to utilize the ability of LED
lighting to be dimmed for off-peak time periods."
There
is almost never a completely satisfactory solution to a complex
problem. We must have lighting at night, not only in our homes and
businesses, but also outdoors on our streets. The need for energy
efficiency is serious, but so too is minimizing human risk from bad
lighting, both due to glare and to circadian disruption. LED technology
can optimize both when properly designed.
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