About Lighting Pollution
The effects of night lighting on wildlife have been known for hundreds, even thousands, of years. Hunters and fishers have used torches, lamps, and other light sources to attract their quarry to them, so powerful is the effect of light on some species. Gas-lit lighthouses have long had the reputation of attracting marine birds by the thousands, as well. But only in the past century, with the advent and spread of electricity, has the problem of artificial night lighting become so pervasive.
All animals and plants on this planet (including humans) are genetically adapted to regular day/night/seasonal cycles that have, in many places on the planet, been completely interrupted by the glow created by artificial lights. Although some animals may capitalize on the lighting, many suffer its effects, and one hundred years is not enough time to genetically adapt to these changes.
To understand the affects of artificial light, we must first understand the difference between diurnal and nocturnal creatures. Diurnal species are species that are primarily awake during the day, and sleep at night. These include animals such as bees, squirrels, songbirds, and even humans. Nocturnal animals sleep during the day, and move about at night. These include animals such as moths, bats, frogs, and cats. Artificial light affects both, but in different ways.
Artificial light has several general effects on wildlife:
- Attracts some organisms (moths, frogs, sea turtles), resulting in them not being where they should be, concentrating them as a food source to be preyed upon, or just resulting in a trap which exhausts and kills them.
- Repels some organisms, excluding them from habitat where they might otherwise make a living. Makes it a form of habitat loss.
- Alters the day/night patterns, resulting in not getting enough sleep, not having enough down time for the body to repair itself, alters reproductive cycles.
Humans can go inside and turn out the lights out to prevent these issues, but the frogs in the pond by the streetlamp can't. For animals that are very site specific, it's not an option to move. They just get eaten, or fail to reproduce. For those that can move, as more and more lighting encroaches on dark areas, the areas that are dark enough to move TO become fewer and further between. Artificial lighting is another form of habitat loss.
Keeping the light LOW (mounting the fixture as low as possible) and SHIELDED (fully shielding the light so bulbs and/or glowing lenses are not visible) cuts down on the amount of glare and light visible to the animals, so that there is less opportunity for them to get trapped, repelled, or have their day/night patterns altered. Keeping it LONG wavelength (ambers and reds) actually makes the light that is visible seem dimmer to nocturnal animals that primarily use rod vision. The rod system's peak sensitivity is at 496 nm, so a low pressure sodium light, with its emitted light at 589 nm, should seem 1/10th as bright to an animal using purely rod vision vs. an animal that uses rods and cones to see (see Publications: Ecological Consequences of Night Lighting, p. 33).
Changing to LOW, SHIELDED, and LONG wavelength lights also results in energy savings. For instance, lights that are lower and shielded often result in more lumens (light) being focused onto the ground, rather than wasted illuminating the sky above the light. Additionally, some long wavelength light sources such as low pressure sodium lights and amber LEDs use a fraction of the energy of their mercury halide, incandescent and even fluorescent counterparts
For more information on specific groups of animals affected by artificial lighting, click on the links below:
Most people are familiar with the saying, "Like a moth to the flame." Artificial lighting is extremely detrimental to many insect populations, acting like a vacuum that they cannot escape. Even one artificial light source can disrupt normal flight activity, long distance migrations, or even attract insects that don't normally move from their habitat. Once the insects are effectively trapped by the light, they can be killed directly by lamp's heat, they may circle the light until caught by predators, or they may stop to rest on the ground under the light, where they are also preyed upon. Distant sky glow may also disrupt their migrations, but no data are available about this potential effect. Light traps are very likely changing the diversity of insects; for instance, in one study, scientists collected 50,000 moths in a single night. If a particular species does not reproduce rapidly enough to make up for the loss at the lights, it may disappear from the community. For insects that are important as pollinators, or predators of nuisance insects, their loss is detrimental to human communities as well.
The effect of artificial lights on birds has been known for centuries. In the past, people used flame and lights to attract birds at night to capture them for food. Since their inception, there have been reports of seabirds attracted to the light beam of lighthouses. Artificial lights can "trap" migratory birds by bleaching their visual pigments, causing them to lose sight of the horizon and circle within the cone of light endlessly. They then can die from exhaustion or collision with the light source. It can extend the day for diurnal species of songbirds, making them more susceptible to predators as they sing out their location, or causing them to breed too early since they associate breeding with longer days. It can attract seabirds away from their normal feeding grounds, possibly because these birds feed on bioluminescent sea animals and are cued in to low levels of light.
The effect of artificial lights on amphibians has not been well studied. However, most frogs are nocturnal, so it is expected that lights have an effect on breeding, feeding, and predator avoidance, as occurs in most other species of animals. Artificial lights have been found to alter nest hiding behavior and possibly calling, affecting their breeding success. Some frogs gather at lights to forage, making them more susceptible to dehydration and predators, (as well as cars).
Most mammals are nocturnal. Studies have found that many small mammals (for example, mice) eat less food in areas that are lit by artificial light, assumedly to avoid predators. Conversely, other studies have found that predators of small mammals (for example, foxes), are attracted to lit areas, possibly for easy prey. Artificial light has also been shown to affect the circadian rhythm of some mammals, extending the day of diurnal species, and shortening the day of some nocturnal species. In rats, artificial light at night suppressed melatonin production, and resulted in an increased rate of tumors.
Bats are well known to be affected by artificial lights. Many species of bats use artificially lit areas as an easy foraging ground, which can affect the local population of insects. Some bats, however, avoid the lit areas, and are then outcompeted by the bats that get increased food from the lit areas.
Even human beings are not immune to the effects of artificial light. As a species, humans are diurnal (which means that we are awake during the day, and sleep at night). Diurnal species feel safer in lit areas while they are awake. But physiologically, humans need a dark cycle too. During the night, in darkened conditions, humans produce melatonin, a necessary hormone that helps the body's cells repair themselves. Serious interruptions in the day/night cycle, such as shift work, have been demonstrated to interfere with melatonin production, resulting in a higher incidence of some cancers such as breast cancer.
Sea turtles are the most well-known species of reptiles that are negatively affected by artificial light. Female turtles nest on subtropical and tropical beaches around the world. About two months later, the hatchlings burst from the nest en masse and start scrambling to the brightest horizon. On a natural beach, this is toward the moon and starlight glimmering off the water, and away from the shadowy dune. Artificial lights cause a problem for hatchlings because they lead the small turtles away from the safety of the water, where they succumb to dehydration, predators, or even being run over by cars. They also affect nesting females, who may spend valuable energy moving toward lights and away from the water instead of returning to the sea after nesting. Tragically, nesting females may also be attracted to roads where they are hit by cars. The loss of a female who has, against the odds, made it to reproductive age is a significant loss to these threatened and endangered populations. For more information on the effects of lights on sea turtles.
Other species of reptiles are also affected by artificial light. For example, geckos are a nocturnal species of reptile that are drawn to light to feed. This, in turn, makes the geckos more susceptible to predators.