Light Pollution: How Dark Is Your Night Sky?

Light pollution is a side effect of industrialization, with sources including building exterior and interior lighting, advertising, commercial properties, offices, factories, streetlights, and illuminated sporting venues. It is a human-made alteration of outdoor light levels from those occurring naturally, and it has harmful effects on humans, wildlife, and our climate. With most of the Earth's population living under light-polluted skies, it is important to understand the magnitude of the problem and take steps to reduce light pollution. There are various ways to measure light pollution, such as using smartphone apps, light pollution maps, and the Bortle scale, which can help individuals and communities make informed choices about lighting and advocate for local legislation to address this issue.

Light pollution maps

There are several online tools and apps available to help you determine light pollution levels in your area. For example, the Light Pollution Map by Dark Sky is a mobile application that helps locate dark sites where the sky is unaffected by light pollution, making it ideal for stargazing, astronomy, and night photography. The app has several features, including a cloud cover overlay, a horizon safe radius tool, and the ability to save and load your favourite dark sky locations. The app also has a unique astronomy photo of the day feature, a night sky calendar, and live aurora webcams.

Another way to measure sky brightness is by using a smartphone application called Clear Outside by FLO. This app uses your current GPS location to present an accurate reading of where your night sky falls on the Bortle scale, a scale that measures the brightness of the night sky for a particular location. The Bortle scale ranges from Class 1, where one can observe the Triangulum Galaxy with the naked eye, to Class 9, which represents inner-city sky conditions.

It is important to note that some light pollution maps use data from the Visible Infrared Imaging Radiometer Suite (VIIRS) instrument aboard the NASA/NOAA satellite, which is not sensitive to white light from LEDs commonly used in street lights. Therefore, light pollution levels may be worse than indicated, especially in inhabited areas.

Sky brightness measurements

There are several methods to measure sky brightness and assess light pollution. One of the most common methods is through the use of photometers and digital cameras. Photometers, such as the SQM photometer, can be handheld or permanently installed in monitoring stations. These devices measure the luminance of the night sky and provide readings in magnitudes per square arcsecond units (MPSAS). The SQM scale typically ranges from 16.00 to 22.00, with lower numbers indicating higher luminance and brighter skies.

Another method involves utilizing satellite imagery from sources such as the Suomi NPP satellite and the Defense Meteorological Satellite Program (DMSP). These satellites employ instruments like the visible/infrared imaging radiometer suite (VIIRS) Day/Night Band and the operational linescan system (OLS) to capture images of the Earth's surface, which can be used to assess light pollution.

Additionally, smartphone applications have been developed to aid in measuring sky brightness. Apps like Dark Sky Meter and Loss of the Night utilize the iPhone camera to record and assess the brightness of the night sky. Other apps, such as Clear Outside, use your GPS location to provide a Bortle class rating, indicating the level of light pollution in your area. The Bortle scale is a nine-level system that uses astronomical observations to measure light pollution, with Class 9 representing the most extreme amount of light pollution.

Furthermore, citizen science programs like Globe at Night encourage individuals to visually assess night-sky brightness using constellation stars and observable details. This data helps raise awareness about light pollution and its impact on sky glow.

While these methods provide valuable information, there is a need for standardized measurements and an autonomous all-sky imaging system to more effectively monitor and compare light pollution levels across different locations.

Light pollution sources

Light pollution is caused by outdoor lights that emit light upwards or sideways. Any light that escapes upward will scatter throughout the atmosphere and brighten the night sky, thus contributing to light pollution. Air pollution particles also increase the scattering of light at night. Light fixtures that direct all light downward greatly reduce the amount of light pollution. These are called shielded lights or full cut-off lights.

Light pollution is a human-made alteration of outdoor light levels from those occurring naturally. There is no single country, group, or industry to blame for light pollution. Instead, it is a result of the entire world's increasing reliance on outdoor electrical lights.

Light pollution has harmful effects on humans, wildlife, and the climate. It can cause visual discomfort, known as glare, and excessive groupings of light sources, called clutter. It can also extend into areas where it is not wanted or needed, such as a streetlight illuminating a bedroom window, which is referred to as light trespass.

Light pollution can be reduced by using less powerful lamps or bulbs, properly shielding outdoor lights, and using outdoor lighting only when and where it is needed. Many states have adopted legislation to control outdoor lighting, and manufacturers have produced high-efficiency light sources that save energy and reduce light pollution. Individuals can also help by closing window blinds, shades, and curtains at night to keep light from escaping outside.

Reversing light pollution

Unlike many other forms of pollution, light pollution is reversible. Light pollution is caused by the excessive use of artificial light at night, which takes a toll on our environment, health, energy resources, and safety. It harms wildlife habitats, human health, and our quality of life. It also prevents us from experiencing the wonder of a truly dark night sky.

To reverse light pollution, we need to take action. Here are some ways to do that:

• Use warm-colored bulbs: LEDs and compact fluorescents (CFLs) can help reduce energy use and protect the environment, but only warm-colored bulbs should be used.
• Targeted lighting: All lighting should be targeted and directed to light up only the intended area. Proper shielding and careful aiming can ensure that the light beam points downward and does not spill beyond where it is needed.
• Light only when needed: Use motion sensors or timers to ensure that lights are only on when they are required.
• Evaluate the need for lighting: Before installing a new light or replacing an old one, ask yourself if you need it. Consider if there are any alternatives to using outdoor lighting fixtures, such as reflective paints or self-luminous markers.
• Support organizations: Organizations like DarkSky International work to reduce light pollution by certifying lighting products, designs, and installations that minimize light pollution. They also educate the public about the harmful effects of excessive artificial light.

By implementing these measures, we can help reverse light pollution and restore the glory of the night sky, improving our environment, health, and quality of life.

Light pollution legislation

Light pollution, also known as "obtrusive light", is artificial light that enters areas where it is unwanted and can obscure the visibility of the stars. Common causes of light pollution include exterior security lights, illuminated advertising, flood lighting, and decorative lighting. This type of light pollution can have adverse effects on human health, wildlife, and the environment.

Recognizing the harmful effects of light pollution, lawmakers and communities have taken steps to mitigate it through legislation and initiatives. Here is an overview of some light pollution legislation and initiatives:

International Dark Skies Association

The International Dark Skies Association (IDSA) is a key organization in the fight against light pollution. They define different components of light pollution, including glare, skyglow, light trespass, and clutter. The IDSA has developed lighting principles and guidelines to help reduce light pollution, which local governments in at least 19 states have adopted. These guidelines include recommendations on lighting fixtures, output standards, wiring, and lighting hours.

State and Local Laws

Many states and local governments in the United States have enacted laws and ordinances to curb light pollution. For example, New York passed the 'Lights-Out' legislation in 2014 to reduce excess light from state-owned buildings. Similarly, Illinois introduced SR 64 in February 2023, encouraging local governments to use energy-efficient light fixtures that reduce unnecessary light.

AB 38 in California

Assemblymember Alex Lee of California's 24th Assembly District has introduced AB 38, legislation aimed at reducing night lighting or Artificial Light at Night (ALAN). This bill ensures that outdoor lighting installations on state buildings are dimmable, equipped with shut-off options, motion-activated, and/or shielded to direct light only where it is needed. AB 38 also addresses the protection of wildlife, human health, and energy conservation.

The "Lightning Plan" in Pennsylvania

Governor Josh Shapiro of Pennsylvania has proposed the "Lightning Plan", which includes multiple initiatives to manage energy costs and ensure reliability and sustainability. One aspect of this plan addresses light pollution by establishing mitigation requirements for new and existing wind energy facilities, aiming to reduce light pollution while adhering to Federal Aviation Administration (FAA) regulations.

"Dark Sky Preservation" in Flagstaff, Arizona

Flagstaff, Arizona, became the first municipality to address light pollution in the 1950s due to its connection to astronomy through the Lowell Observatory. In 1958, Flagstaff pioneered dark sky preservation with a lighting ordinance designed to protect the night sky. The city has since received international recognition for its efforts in conserving the natural darkness of the night sky.

These legislative and community initiatives demonstrate a growing awareness of the impact of light pollution and a commitment to finding solutions. By implementing lighting standards, utilizing energy-efficient fixtures, and considering the timing and positioning of lighting, communities can reduce light pollution, protect wildlife and human health, and preserve the beauty of the night sky.

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