What is Light Pollution?
For much of Earth’s history, our remarkable universe of stars has been visible in the darkness of the night sky. But increasing urbanization, combined with the excessive and inefficient use of light, has created a kind of pollution that obscures the stars from view and leads to numerous other disturbances.
Known collectively as “light pollution,” there are three main components: sky glow, light trespass and glare.
- Sky Glow = brightening of the night sky over inhabited areas.
- Light Trespass = light that shines where it is not needed or wanted.
- Glare = excessive brightness that causes visual discomfort.
Effects of Light Pollution
Astronomers recognized light pollution as a problem in the 1970s. Even with the most powerful instruments, they could no longer view stars and other celestial objects with the same clarity. While at least 2,500 stars should be visible under normal nighttime conditions, only a few hundred can be seen in a typical American suburb. In most large cities, residents would be lucky to glimpse a few dozen. But the adverse effects of light pollution extend well beyond our view of the night sky. Aside from the energy wasted, excess lighting can have serious consequences for human health and the environment. It can even affect the ability of our military to train effectively.
Billions of dollars are spent in the U.S. each year to light our streets, shopping areas, office complexes and sites used for energy development. Unfortunately, since many light fixtures are either poorly designed or emit light aimed in the wrong direction, much of what we spend on outdoor lighting is wasted.
Humans and Wildlife
For humans, exposure to bright light at night can interfere with natural circadian rhythms (i.e. 24-hour day/night cycle) by suppressing production of melatonin, the chemical that regulates sleep patterns. Research has linked this disruption to sleep disorders, depression, obesity, breast cancer and more.
Wildlife is also harmed by light pollution. The decline of lightning bugs (or fireflies), the death of birds during migration, and the fatal disorientation of newly hatched sea turtles are only a few examples.
Light pollution can also limit the military’s ability to conduct nighttime training at bases around the country. In fact, with the use of night-vision equipment, a significant portion of military training is now conducted at night. These exercises simulate combat situations, helping troops develop their situational awareness and ultimately minimize casualties. The impact of light pollution on military training will undoubtedly increase as residential and commercial development in nearby communities continues to grow.
At least 19 states, the District of Columbia and Puerto Rico have laws in place to reduce light pollution. The majority of states that have enacted so-called “dark skies” legislation have done so to promote energy conservation, public safety, aesthetic interests or astronomical research capabilities. In 2021, 17 states considered 40 bills with reference to light pollution or dark skies. Municipalities in a number of states have also been active on this issue, adopting light pollution regulations as part of their zoning codes.
Most state laws are limited to outdoor lighting fixtures installed on the grounds of a state building or facility or on a public roadway. The most common dark skies legislation requires the installation of shielded light fixtures which emit light only downward. Replacement of unshielded with fully shielded lighting units often allows for use of a lower wattage bulb, resulting in energy savings. Other laws require the use of low-glare or low-wattage lighting, regulate the amount of time that certain lighting can be used, and the incorporation of Illuminating Engineering Society (IES) guidelines into state regulations.
Known as a worldwide hub for astronomy, Arizona’s light pollution law dates back to 1986 (Ariz. Rev. Stat. Ann. §§49-1101 et seq.). The law requires all outdoor light fixtures to be fully or partially shielded, with the exception of emergency, construction and navigational airport lighting. Fixtures not in compliance are allowed provided they are extinguished between the hours of midnight and sunrise by automatic device. Some laws are more specific than others. For example, in Colorado, installation of new outdoor lighting fixtures requires consideration of costs, energy conservation, glare reduction, minimizing light pollution and the preservation of the natural night environment (Colo. Rev. Stat. §§24-82-901 et seq.). A “full-cutoff fixture” must be used when output is greater than a certain amount of lumens.
Other states have sought to encourage these types of measures at the local level. New Hampshire, for example, has made it a priority to preserve dark skies as a feature of rural character. To that end, state law encourages municipalities to adopt ordinances and regulations to conserve energy and minimize light pollution (N.H. Rev. Stat. Ann. §9-E:3). The effect of beachfront lighting on avian and marine life is also a concern in many coastal states. In Florida, for example, a statewide model lighting ordinance (Fla. Stat. §161.163; Fla. Admin. Code §§62B.55.001 et seq.) guides local governments in developing policies to protect hatching sea turtles.
Texas is the only state with a law in place specifically aimed at reducing light pollution around military installations. In 2007, the Texas Legislature amended an existing law regarding the regulation of outdoor lighting to authorize state counties, at the request of the military, to adopt measures governing the use of outdoor lighting within five miles of a military installation (Tex. Local Government Code Ann. §240.032). The provision only applies to counties with at least five military bases and a population of more than 1,000,000 people or adjacent counties located within five miles of a base. County regulations must be designed to protect against interferences with military training activities. Counties may accomplish this goal in a number of ways: (1) require that a permit be obtained before installing certain types of lighting; (2) prohibit the use of particular lighting fixtures; (3) establish requirements for the shielding of outdoor lighting; or (4) regulate the times during which certain types of lighting may be used.