Many of us are already aware of declining populations of pollinators and other beneficial fauna and flora due to human development, pesticide use, and climate change. However, a lesser known but equally important cause of these declines is the use of artificial light at night. This light pollution is endangering pollinators, as well as mammals, birds, amphibians, and plants, because they depend on Earth’s daily cycle of light and dark for food, reproduction, sleep, and navigation.

Light pollution harms pollinators in a number of ways. Nocturnal moths are drawn to light and are prone to visit lights instead of pollinating flowers. Other pollinators, such as some species of pollinating beetles, avoid flowers under artificial light; as a result, plants exposed to nighttime artificial light do not receive enough visits from pollinators. This results in these plants to be less stimulated to produce pollen, which then diminishes the amount of pollen available as a food source for diurnal pollinators such as bees and butterflies. Light pollution also reduces pollinators’ sleep and recovery time, making it more difficult to survive and reproduce. In addition, light pollution alters the ability of plants to sense and react to natural light, which can harm their ability to flower and provide food for pollinators.

Furthermore, light pollution is causing declines in populations of fireflies (also called lightning bugs). Fireflies are bioluminescent—they create light of their own to find mates. Light pollution obscures this natural firefly bioluminescence, making their populations more vulnerable by reducing their ability to find mates.

Light pollution doesn’t only affect insects. It can cause birds to migrate at the wrong time. It can also disorient migrating birds, luring them off course and causing them to collide with illuminated buildings. Light pollution can even cause sleep disorders in humans, with negative consequences for our own health.

While artificial light makes many of us feel safer, there is no evidence that increased outdoor night lighting deters crimes. Studies conducted by the Illinois Criminal Justice Information Authority, the American Medical Association, and a variety of university researchers found no evidence that increased outdoor lighting deters crimes. In fact, a significant amount of property crime occurs during the day. Moreover, some studies have found artificial light actually decreases safety by making victims and property easier to see.

Reducing nighttime light pollution will benefit wildlife and humans alike. In addition to improving our health, it will allow us to better appreciate the beautiful night sky and to enjoy June evenings as fireflies sparkle in our yards. Here are some steps we can all take to help:

• Use longer-wavelength LEDs (red spectrum) instead of bright-white lights. These will lessen impact on both wildlife and humans.
• Use timers or motion sensors on outdoor lighting, so that lights turn on only when necessary.
• Use outdoor lighting fixtures that shield the light, so they minimize glare and directly illuminate the target.
• Keep outdoor lights low to the ground (no higher than 10 feet) and use dimmers.
• Turn off unnecessary indoor lighting, such as in empty rooms, and use curtains to prevent indoor light from being seen outside.