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How Does Outdoor Lighting Cause Light Pollution?
Light pollution, also known as photopollution or luminous pollution, is the
excessive, misdirected or invasive use of artificial outdoor lighting.
Mismanaged lighting alters the color and contrast of the nighttime sky, eclipses
natural starlight, and disrupts circadian rhythms (the 24-hour processes of most
organisms), which affects the environment, energy resources, wildlife, humans
and astronomy research. The threat of light pollution continues to grow as the
demand for artificial light increases each year.
Photopollution is not a new phenomenon. Over the last 50 years, as countries
became affluent and urbanized, demand for outdoor lighting increased and light
pollution sprawled beyond the city limits and into suburban and rural areas.
This form pollution is now prevalent in Asia, Europe, and North America,
particularly in cities like Los Angeles, New York and Washington D.C. In 2008,
National Geographic magazine named Chicago the most light-polluted city in the
United States.
However, the most light-polluted spot in the world is Hong Kong, China. In March
2013, the University of Hong Kong named the city the most light polluted in the
world. A study by the university found the night sky in Tsim Sha Tsui, an urban
neighborhood in southern Kowloon, Hong Kong, to be 1,200 times brighter than a
normal urban city sky. Luminous pollution of this magnitude is on the rise
worldwide. In a 2010 article from the
Ecology and Society Journal, Hölker and others stated the use of artificial
lighting increases by 20% each year, depending on the region, and noted there is
an urgent need for light pollution policies that surpass energy efficiency to
include humans, animals and the environment.
As many homeowners, you are taking steps to reduce your carbon footprint at
home. You dutifully recycle glass, metal, paper, and plastic waste each week.
You replace all the incandescent light bulbs in your home with energy-efficient
compact fluorescent lamps (CFL) or
LED light
bulbs. However, you may be unwittingly contributing to carbon emissions and
interfering with delicate ecosystems through light pollution.
Light pollution, unlike other forms of contamination and waste, remains largely
overlooked and unregulated in many countries. Learn the cause, types, and
effects of light pollution, and how adjusting your outdoor lighting habits can
reduce this form of waste with the information below:
Causes of Light Pollution
Luminous pollution is caused by using outdoor lights when and where they are not
necessary. Poorly designed residential, commercial, and industrial outdoor
lights also contribute significantly to light pollution. Unshielded light
fixtures emit more than 50% of their light skyward or sideways. In many
instances, only 40% of the light emitted actually illuminates the ground.
It is estimated that nearly 30% of outdoor lighting is wasted due to this poor
design. In the United States alone, wasted lighting accounts for 1.7 million
tons of carbon dioxide and $2.2 billion in wasted electricity each year.
Types of Light Pollution
Photopollution occurs in a variety of forms, including light trespass, glare,
sky glow, and light clutter. One source of light can result in multiple forms of
pollution. Here is how you can identify each form of light pollution.
1. Light Trespass
Light trespass, also known as spill light, occurs when a light fixture casts
illumination beyond the property lines, unintentionally illuminating other
homes, businesses, or areas. Spill light is the most subjective form light
pollution because there are no guidelines to determine when, where, or how much
light is unwanted. A common example of spill light is light from a streetlight
coming through a window and illuminating a bedroom, light from
outdoor wall lights that direct light up
towards the sky rather than towards the ground, or light from a neighbor's
floodlight or
security light shining over the fence
and illuminating your property.
2. Glare
Glare is the visual sensation one experiences when stray light, light in the
visual field, is greater than the light to which the eyes are adapted. Glare,
depending on the intensity, can result in reduced contrast, color perception,
and visual performance.
Glare occurs in the following three forms:
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Discomfort Glare – Discomfort glare is also known as
psychological glare, and is the most common type of glare. Psychological glare
occurs when lighting causes annoyance or irritation, but does not decrease
visual performance and physical discomfort is short term. Reduce discomfort
glare by installing a light dimmer to dim lights, such as
recessed lights, in your home.
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Disability Glare – Disability glare, also known as veiling
glare, occurs when stray light scatters in the eye, producing a veil over the
retina, affecting visual performance. Veiling glare reduces contrast as well as
color and spatial perception, which can lead to unsafe driving conditions. Older
drivers are more prone to experience disability glare while driving.
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Blinding Glare – Blinding glare, also known as absolute glare
or dazzle, occurs when a light source impairs the field of vision, preventing
the eye from seeing anything but the light source. Visual performance may remain
affected for some time well after the incident.
3. Sky Glow
Sky glow originates from natural and man-made sources; however, poorly designed
and targeted artificial lights are the main cause of sky glow. Sky glow occurs
when light is emitted directly into the atmosphere, accidently or purposefully,
where it is scattered by dust and gas molecules, creating a dome-like orange
glow that covers the night sky. The glow reduces the contrast between the stars
and the galaxies in the sky, making celestial objects difficult to see even with
a telescope. Light domes also affect the polarization of moonlight, which
nocturnal animals use to navigate.
Glow domes are visible in cities and towns throughout the world, and they appear
in a variety of sizes such as large domes over metropolitan hubs or small domes
above over-illuminated commercial areas and sport complexes or stadiums. Cloud
coverage, snow, trees, and the quantity of dust and gas molecules in the
atmosphere can amplify sky glow.
According to the National Park Service, artificial sky glow from major cities is
visible up to 200 miles away in many national parks. For example, the bright
lights of Las Vegas are visible in Nevada’s Great Basin National Park, located
295 miles west of the city, and in California’s Death Valley National Park,
located 118 miles west of the city. The lights are even visible in the Bryce
Canyon National Park in Utah, known as one of the darkest spots in North
America, located over 260 miles northeast of the city.
4. Light Clutter
Light clutter is the excessive grouping of bright lights that cause confusion
and distract from oncoming or surrounding objects. Light clutter is visible on
roads surrounded by unshielded street lights and brightly lit advertisements or
signs. This creates a hazardous environment for drivers and pilots because it
competes with traffic and navigation signals. Clutter contributes to other forms
of light pollution, including light trespass, glare, and sky glow.
How to Measure Light Pollution? The Bortle Dark Sky Scale
Measuring light pollution is an intricate process because the natural atmosphere
is not completely dark due to airglow and scattered light. To obtain an accurate
measurement, scientists use satellite images of Earth at night to determine the
number and intensity of the light sources, and calculate the total sky
brightness.
Amateur and professional astronomers can also use a Sky Quality Meter, a
handheld device that measures sky brightness, to document and compare different
areas. Mobile apps like Dark Sky Meter and Loss of Night allow anyone to measure
sky brightness.
Another way to gauge light pollution is the Bortle Scale, a nine-level rating
system that measures sky quality by providing observable standards. John E.
Bortle, a retired fire chief and amateur astronomer, devised the rating system
in 2001 as a means to help amateur astronomers evaluate the darkness of an
observation site and compare sites. The scale ranges from one, an excellent
dark-sky site, to nine, an inner-city sky, and specifies observable criteria for
each class.
Effects of Light Pollution
Luminous pollution has dire effects on our environment and resources of energy
as well as wildlife ecology and astronomical research. Light pollution also
affects the quality of life and safety of humans. Here are some of known side
effects of light pollution.
Environment
The International Dark-Sky
Association (IDA), a non-profit organization that raises awareness of light
pollution, estimates that excessive nighttime lighting releases more than 12
million tons of carbon dioxide, the most serious greenhouse gas, into the
atmosphere each year. It would take nearly 702 million trees to absorb the
carbon dioxide produced by wasted light.
Light pollution may also contribute to other forms of pollution. According to a
2010 study by the National Oceanic and Atmospheric Association, photopollution
increases air pollution by suppressing a naturally occurring radical that cleans
the air at night. Nitrate radical, a form of nitrogen oxide, breaks down vehicle
and factory emissions at night. The nightly process prevents the emissions from
becoming smog, ozone pollution, or other harmful irritants. The process only
takes place at night because sunlight destroys nitrate radical. However,
artificial lights from buildings, cars, and streetlights, although 10,000 times
dimmer than sunlight, also affect nitrate radical and slow down the cleansing
process by 7%. Artificial light also increase the chemicals for ozone pollution
by 5%.
Energy
Wasted light results in energy waste. A 2007 IDA study estimated that 30% of all
light emitted by public outdoor light fixtures is wasted, which amounts to 22
Terawatt Hours (TWh)/year of wasted electrical energy. This is equivalent to the
following:
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About 3.6 million tons of coal per year
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About 12.9 million barrels of oil per year
The total amount of wasted electrical energy each year is enough to illuminate
over 11 million homes and power over 777,000 cars.
Wildlife
Luminous pollution affects the feeding, sleeping, mating, and migration cycles
of all wildlife. Wildlife can also experience disorientation of time when there
is too much artificial light at night.
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Mammals - Mammals such as bats, raccoons, coyotes, deer, and
moose can experience difficulty foraging for food at night due to over
illumination. They risk exposure to natural predators and increased mortality
due to night vision impairment. They also experience a decline in reproduction
that leads to a shrinking population.
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Birds - Birds such as owls and nighthawks use moonlight and
starlight to hunt and migrate at night. Artificial lights sources can overwhelm
natural light sources, causing birds to be drawn to or fixated on the artificial
lights. This results in birds deviating from their intended migration route,
flying until they experience exhaustion and collapse, and becoming prey to other
animals. Marine birds such as albatrosses are known to collide with lighthouses,
wind turbines, and drilling platforms at sea due to their bright lights. In
North America alone, 100 million birds die annually in collisions with
illuminated buildings and towers.
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Amphibians - Sky glow affects amphibians such as frogs, toads,
and salamanders in marshes and wetlands. The orange haze confuses and disorients
them, which causes a decrease in feeding and mating. It also impairs natural
instincts that protect amphibians against natural predators and the elements.
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Reptiles - Reptiles such as sea turtles are greatly affected by
light pollution. Female turtles nest on dark, remote beaches, but bright coastal
lights prevent them from finding safe nesting areas for their eggs. This leads
the female turtles depositing their eggs in an unsafe area or the ocean. Sea
turtle hatchlings instinctively crawl toward the brightest part on the beach,
which for many centuries was the moonlight and starlit ocean; however, excessive
lighting on the beach or near the shore confuses the hatchlings and causes them
wander away from the ocean. The hatchlings may be eaten by predators, run over
by vehicles, drown in swimming pools, or die from dehydration or exhaustion.
Artificial lights may also disorient other nocturnal reptiles.
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Insects - Insects such as moths are naturally attracted to
light and may use all their energy to stay near a source of light. This
interferes with mating and migration as well as makes them vulnerable to natural
predators, which reduces their population. This also affects all species that
rely on insects for food or pollination.
Astronomy
Light pollution alters our view of the sky and stars, but no group of people is
more affected by this phenomenon than astronomers. Light spill and sky glow
interferes with astronomical equipment, and makes viewing faint celestial bodies
difficult even with the aid of a telescope.
Astronomy is one of the oldest sciences in human history, and has made countless
contributions to technology, economy and society with applications like personal
computers, communication satellites, mobile phones, Global Positioning Systems
(GPS), solar panels, and Magnetic Resonance (MRI) scanners.
Today, astronomy helps us determine the Sun's effect on Earth's climate, and
identify any potential threats to Earth from space. In order to conduct
observation and research, astronomers require dark skies.
Humans
Humans, like plants and wildlife, are regulated by circadian rhythms, the
physical, mental and behavioral changes that occur in a 24-hour cycle. The
circadian clock regulates physiologic activities such as brain wave patterns,
hormone production, and cell regulation. The rhythms respond to the light and
darkness around an organism. Disrupting these rhythms can result in a variety of
health problems, including sleep disorders, anxiety, depression, diabetes,
cancer (particularly breast and prostate cancer), cardiovascular disease,
immunological disorders, and obesity.
Melatonin, the naturally occurring hormone that regulates the sleep and wake
cycle, is acutely affected by light pollution. The hormone is activated by
darkness and repressed by light. Melatonin deficiency can result in anxiety and
mood disorders, insomnia, and elevated estrogen/progesterone ratio.
In 2009, the American Medical Association (AMA) unanimously supported the
reduction of light pollution, and advocated the development of energy-efficient
outdoor lighting to reduce glare and energy waste.
The Dark-Sky Movement
The dark-sky movement is a grass roots movement by professional and amateur
astronomers to reduce light pollution. The movement raises awareness about the
effects of photopollution and advantages of cutting down on energy usage. The
following groups and events are at the forefront of the dark-sky movement and
light pollution awareness:
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International Dark-Sky Association (IDA) - Founded
in 1988, the IDA is a non-profit organization recognized as the authority on
light pollution and night-sky conservation. The organization is responsible
developing the following campaigns to raise awareness about luminous pollution:
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Fixture Seal of Approval (FSA) - A program that
review and certifies outdoor lighting fixtures based on strict criteria to
determine sky friendliness. Dark-sky compliant lights are fully shielded and do
not emit illumination above a horizontal plane. These lighting fixtures provide
color temperatures 4100K CCT or below. Manufacturers like
Minka Lavery offer beautiful
dark sky approved outdoor light fixtures.
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Dark-Sky Places - Parks, reserves, and communities
that have exceptional or distinguished quality skies, and are protected for
scientific, natural, educational, cultural heritage, and/or public enjoyment.
IDA certified dark-sky places adhere to strict lighting codes and regulations,
and promote anti-photopollution education. Dark-sky parks and reserves have been
established in Hungary, Namibia, New Zealand, Scotland, Slovakia, United
Kingdom, and the United States. Flagstaff, AZ, Borrego Springs, CA, Homer Glenn,
IL, and the Island of Sark, Channel Islands, UK, have been certified as dark-sky
communities.
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Campaign for Dark Skies (CfDS) - Founded by the
British Astronomical Association in 1989, the
Campaign for Dark Skies is the United Kingdom's largest campaign against
light pollution. The group is affiliated with the IDA and works with the House
of Commons Science and Technology Committee to adopt legislation that reduces
photopollution.
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Globe at Night - Founded by the National Optical
Astronomy Observatory, the Globe at Night is an international research
project that asks members to choose the star-chart number, 1 through 7, which
best represents what they can see toward the constellation on the month. More
specifically, which chart shows the faintest star the individual can see. Based
on which stars can shine through the surrounding light pollution scientists
can compile the information to produce free, public maps detailing global light
pollution based on a scale. #1 represents the areas with the most light
pollution, like New York City. Chart #7 shows up in areas like national parks
where light pollution tends to be very low. The Globe at Night is also a great
resource for teachers and parents to gather information to teach children about
light pollution.
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Royal Astronomical Society of Canada
(RASC) - Established in 1898 in Toronto, Ontario, Canada, the
Royal Astronomical Society of
Canada boasts 4,000 members and 29 astronomy centers that provide astronomy
education and outreach. In 1991, RASC founded Light-Pollution Abatement Program
(LPA) to establish responsible lighting practices that reduce light pollution.
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National Dark-Sky Week - A week long annual
celebration held during the new moon in April to raise awareness about light
pollution. Founded in 2003 by Jennifer Barlow of Midlothian, Virginia, a high
school student at the time, the event encourages participants to turn off their
lights and observe the night sky without light pollution.
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Earth Hour - First organized by the Worldwide Wide
Fund for Nature (WWF) in 2007,
Earth Hour is an annual event
that encourages people to turn off lights for one hour to raise awareness about
climate change. The occasion is observed in nearly 7,000 cities worldwide.
7 Tips to Prevent Light Pollution
Luminous pollution, unlike other forms of contamination and waste, can be
contained and/or reduced by improving outdoor lighting practices. Remember that
outdoor lighting serves a purpose - to provide visibility and safety at night,
but lighting that exceeds its purpose can quickly become offensive to others.
Here are some simple tips to help you reduce light pollution without sacrificing
your comfort or safety.
1. Warm It Up
Use compact fluorescent lamps (CFL)
and LED bulbs that produce warm white lighting. Many LED lights emit a blue
short wavelength light that scatters easily into the atmosphere, which causes
eyestrain, impairs night vision and adds to light pollution.
2. Shield It
Choose outdoor light fixtures that are shielded, meaning there is a solid cap
above the light bulb that prevents light from being emitted directly to the sky,
to minimize sky pollution. You can shield exiting fixtures by buying and
installing reasonably priced shades.
3. Cut It Off
Select exterior light fixtures with cutoff angles to prevent light from escaping
above the horizontal plane (nadir), minimize uplighting, and reduce high-angle
brightness. Cutoff lighting emits illumination down to the ground where it's
most needed and in many cases, improves visibility. The
Illuminating Engineering
Society of North America (IESNA) provides the following cutoff
classifications:
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Full Cutoff - No light is distributed at or above an angle of 90 degrees
from the nadir. Candela per 1000 lamp Lumens does not numerically exceed 100 (10
percent) at a vertical angle of 80 degrees from the nadir. This applies to all
lateral angles around the light source.
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Cutoff - Cutoff light fixtures allow a small amount of uplighting.
Candela per 1000 lamp Lumens does not numerically exceed 25 (2.5
percent) at a vertical angle of 90 degrees from the nadir. Candela per 1000 lamp
Lumens does not numerically exceed 100 (10 percent) at an angle of
80 degrees from the nadir. This applies to all lateral angles around the light
source.
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Semi-Cutoff - Semicutoff light fixtures emit more light directly into the
sky and provide little control at the property line. Candela per 1000 lamp
Lumens does not numerically exceed 50(5 percent) at an angle of 90
degrees from the nadir. Candela per 1000 lamp Lumens does not
numerically exceed 200 (20 percent) at an angle of 80 degrees above nadir. This
applies to all lateral angles around the light source.
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Non-Cutoff - Noncutoff light fixtures distribute light without
Candela limitation in the zone above the max Candela.
4. Sensor It
Install motion sensors on outdoor fixtures so they turn on when needed and turn
off after a short time. Make sure to test and adjust the motion detector's
sensitivity as needed to prevent the lights from turning on and off
unnecessarily.
5. Get Certified
Use IDA certified Dark Sky Lighting, which is designed to
minimize glare, light spill, and sky glow. Dark-sky approved light fixtures are
available in a variety of chandeliers, flush mounts, pendants, and wall sconces.
If you live near the beach, use certified Turtle Safe Lighting. These shielded
light fixtures produce a long wavelength light, which does not scatter easily,
and should be mounted low to avoid high-angle brightness.
6. Turn It Off
Turn off any unnecessary outdoor lights when you are home for the night or
before going to bed to prevent wasteful dusk to dawn lighting. If you're in
doubt, turn them off by 11 PM. While you're at it, make sure to turn off indoor
light fixtures, like wall lights, when you're not home or before
bed to reduce energy consumption.
7. Be Involved
Take steps to prevent and reduce light pollution in your home, work, and
community. Close the blinds and curtains to prevent light spill. Ask management
to turn off or dim office lights after all workers have left the property for
the day to prevent light and energy waste. Petition local business owners to dim
after-hour signs to prevent glare and light clutter. Propose lighting ordinances
to your local and state governments to reduce light pollution.
Sources
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Amos, Jonathan. "City lighting 'boosts pollution'."
BBC News, December 14, 2010. Accessed November 19, 2013.
http://www.bbc.co.uk/news/science-environment-11990737.
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Bortle, John E. "The Bortle Dark-Sky Scale." ,Sky
and Telescope, February 2001. Accessed November 19, 2013.
http://www.skyandtelescope.com/resources/darksky/3304011.html.
-
Earth Hour. "About | Earth Hour." Accessed November 19, 2013.
http://www.earthhour.org/page/about.
-
GLOBE at Night. "About GLOBE at Night." Accessed November 19, 2013.
http://www.globeatnight.org/.
-
Hölker, Franz, Timothy Moss, Steffen Franke, Dirk Uhrlandt, Jürgen Fischer,
Reinhard Klenke, Christian Wolter, Klement Tockner, Barbara Griefahn, Werner
Kloas, Christian C. Voigt, Dietrich Henckel, Andreas Hänel, Peter M. Kappeler,
Stephan Völker, and Axel Schwope . "The Dark Side of Light: A Transdisciplinary
Research Agenda for Light Pollution Policy ." Ecology and Society 15, no. 4
(2010). http://www.ecologyandsociety.org/vol15/iss4/art13/ (accessed November
19, 2013).
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International Dark-Sky Association.
What Is Light Pollution? Tucson, AZ: International Dark-Sky Association.
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International Dark-Sky Association.
Light Pollution and Wildlife. Tucson, AZ: International Dark-Sky
Association, 2008.
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International Dark-Sky Association.
Light Pollution and Energy. Tucson, AZ: International Dark-Sky Association,
2008.
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International Dark-Sky Association.
Light Pollution and Human Health. Tucson, AZ: International Dark-Sky
Association, 2008.
-
International Dark-Sky Association. "International Dark Sky Places." Accessed
November 19, 2013.
http://www.darksky.org/night-sky-conservation/34-ida/about-ida/142-idsplaces.
-
International Dark-Sky Association. "About IDA’s Fixture Seal of Approval."
Accessed November 19, 2013. http://www.darksky.org/outdoorlighting/72-fsa.
-
Lighting Research Center. "Light Pollution." Accessed November 19, 2013.
http://www.lrc.rpi.edu/programs/nlpip/lightinganswers/lightpollution/abstract.asp.
-
National Park Service. "Lightscape / Nigh Sky." Accessed November 19, 2013.
http://www.nps.gov/grba/naturescience/lightscape.htm.
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Paulin, Douglas. "Full Cutoff Lighting: The Benefits."
LD+A 10, no. 4 (2001): 54-56. doi:
http://www.iesna.org/PDF/FullCutoffLighting.pdf.
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Royal Astronomical Society of Canada. "Light-Pollution Abatement." Accessed
November 19, 2013. http://www.rasc.ca/lpa.
-
The Campaign for Dark Skies. "About the Campaign for Dark Skies." Accessed
November 19, 2013. http://www.britastro.org/dark-skies/about.htm?1O.
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