by Lewis Young

Artificial outdoor lighting at night can cause light pollution. What is light pollution? It is generally defined as unwanted consequences of outdoor lighting and includes such effects as sky glow (brightening of the sky), light trespass (light reaching areas where it’s not needed or wanted), glare (excessive brightness causing visual discomfort and decreasing visibility), and visual clutter (bright, confusing and excessive grouping of light sources). While humans may experience the impacts of light pollution, the interruption of the natural daylight cycle impacts wildlife far more. For wildlife, the cycle of darkness and a connection to the stars is necessary for survival.

All animals depend on a regular interval of daylight and darkness for proper functioning of behavioral, reproductive, and immune systems. This regular interval of daylight and darkness is known as the circadian system and it is impacted by artificial outdoor lighting. The effects of strong outdoor lighting can persist for up to 120 miles. It has been estimated that upwards of 1/3 of the world’s population cannot see the Milky Way due to light pollution around populated areas. The extent of strongly lighted areas in the U.S. are shown in Figure 1.

Figure 1. Strongly lighted areas in the U.S.

Some direct effects are that it disorients and distracts, triggers reproductive behaviors at the wrong periods, frustrates behavior around feeding and pollination, and alters migration.

Pollinators are impacted by light pollution.  Bees, moths, and various other insects do most of our pollination. The importance of pollinators is hard to overstate. Albert Einstein, considered a smart guy by most people, is quoted as saying “No more bees, no more pollination, no more plants, no more animals, no more man.” Bees need sleep just like humans and excessive artificial light at night can lead to sleep deprivation for them.

One study compared nocturnal pollinators in lit vs unlit meadows. The lit meadow showed 62% less visits by pollinators, 29% fewer species of pollinators, and 13% less fruits in the plant species studied.

Another effect of artificial outdoor lighting is that many pollinators are attracted to these sources at night where they may starve due to lack of plants and they are also much more likely to be eaten by bats that have learned to forage at these lighted sites.

Aquatic organisms are also impacted by light pollution. Zooplankton migrate upwards in the dark to eat algae then retreat to darker depths during daylight.  Without these normal zooplankton movements due to excessive light, algae blooms can occur.

Birds are one of the most impacted groups. Effects on birds include altering their reproductive cycle, changing the timing of moult, and interfering with migration. Birds can be “trapped” in the glare of excessive lighting and can’t find their way out. One notable example is the huge twin towers of light at the 9-11 memorial in New York City. Audubon worked out a deal with the facility operators to periodically turn the lights off to allow birds to escape.

Light pollution is the easiest type of pollution to reduce or eliminate. There are many ways to do this. Use window coverings on buildings at night, don’t overlight, and make sure all outdoor lighting is oriented downward and Dark-Sky compliant. Maintain as much overnight dark as possible. Turn outdoor lights off especially during peak bird migration periods and when it’s cloudy or inclement weather. Switches and timers can be used to control timing of lighting at night. Since birds use green and blue wavelengths, avoid when possible white and red wavelengths; these interfere with bird migration. The design of outdoor lighting can go a long way toward reducing impacts to wildlife. In our area, both Glacier and Watertown National Parks have been designated as Dark-Sky parks by the International Dark Sky Association due to their efforts to reduce light pollution.

Light pollution is likely a contributor to the documented loss of 3 billion birds over the last few decades. By being aware of the problem and using carefully designed artificial outdoor lighting we can start reducing the impacts to wildlife.

This article based on information from a presentation by Jane Slade at the 2020 The Wildlife Society Annual Conference.