Taking Bearings

The Cosmos reveals
a canvas of past starlight
under dark night skies,
Prometheus stole fire
now we obscure divine light

More than 80 percent of Americans and 60 percent of Europeans are no longer able to see the Milky Way at night. According to the recently published  World Atlas of Artificial Night Sky Brightness, about one third of all people in the world cannot see the diffuse light of the Milky Way in the night sky due to obscuring atmospheric pollution — including light pollution — that creates sky glow.

Photo Credit: University of Texas McDonald Observatory

Light pollution, also known as photopollution and luminous pollution, is commonly defined as artificial light that is excessive in intensity or spectral range, or inappropriately directed or reflected skyward. A form of environmental pollution, light pollution creates sky glow that obscures dimmer background stars and other celestial bodies, and detrimentally impacts atmospheric chemical processes, plant physiology, animal behaviors, and human health and safety. The sources of light pollution have increased in both in number and intensity, reaching a point at which the combined sky glow produced by artificial sources of light overwhelms or obscures natural light coming from stars, Earth’s moon (reflected sunlight), and zodiacal light (light from the sun scattered by interplanetary dust in our solar system).

Photo Credit: University of Texas McDonald Observatory

The International Dark-Sky Association (IDA) estimates that more than 75 percent of sky glow results from such poorly designed or improperly installed light fixtures. The IDA recommends that lighting professionals and homeowners follow basic principles in lighting to minimize the effects of light pollution: light only when needed, light only the specific area needed, use lights no brighter than necessary, minimize blue light emissions, and fully shield (point downwards) all lighting.

A brighter night sky can adversely affect the habits of both animal and plant life. Increased brightness can change animal feeding, migration, and reproduction habits. In addition to unwanted atmospheric light pollution,  excess and misdirected lighting from poorly placed or focused lights. Building over-illumination, or unnecessary power-consuming lighting during non-working hours can both reduce privacy and disrupt nighttime sleep in animals and humans.

Increased atmospheric brightness can inhibit reactions where nitrate radicals break down chemical substrates that contribute to ozone and smog pollution. Researchers at the Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder have shown a decrease in atmospheric cleansing reactions in areas of substantially increased illumination of the night sky (e.g., highly urbanized or industrialized areas). Global light increased an average of 2.2 percent each year since 2012 according to researchers at the German Center for Geosciences (GCG).

Excess glare can also impact visual acuity because glare (also described as the contrast between a brighter area and relatively darker background surroundings) impairs the human eye’s ability to adjust to the darkness after being exposed to bright lights at night. This recovery time tends to increase with age and as a consequence the “light blindness” can make nighttime driving more hazardous for older motorists. In some high-density urban areas, the light pollution is so significant that residents can never achieve complete night vision adaptation in their eyes when outdoors at night.

In the United States, the first week of April is designated as National Dark Sky Week. The week is designed to highlight the consequences of light pollution, encourage the reduced use of lighting at night, and encourage the use of light bulbs that illuminate with less electricity.

Research continues into the impacts of light pollution on humans. The American Medical Association currently recommends a color temperature of no greater than 3000K for LED street lighting to minimize light pollution and potential health complications from high-CT LEDs including glare, retinal damage, and circadian rhythm disruption.