Human World

Dim the lights for pollinators and plants at night

Dim the lights: Night sky with glowing band of Milky Way over a horizon with a pronounced bright glow along it.
Artificial lights create skyglow at night. Here, skyglow obstructs the view of the night sky over Flagstaff, Arizona. How to dim the lights, here. Photo courtesy of Deborah Lee Soltesz/ USFWS.

Original article by Joanna Gilkeson at the U.S. Fish and Wildlife Service. Edits by EarthSky.

Dim the lights

Wildlife, plants and insects evolved to coexist with the night sky, illuminated by the stars and moon. But humans have transformed the dark. And artificial lights have brightened naturally lit night skies.

In 2016, 80% of the world was estimated to live under skyglow. That’s a term used to describe the brightening of the night sky in places where people live. The same year, the National Oceanic and Atmospheric Administration reported that an estimated 1/3 of humanity could no longer view the Milky Way galaxy. In areas where this occurs, human-produced light obscures the soft glow of more than 100 billion stars.

This excess of light at night is a form of pollution that can harm wildlife and plants.

Artificial light pollution is caused by any kind of outdoor lighting. That may include streetlamps, porch lighting and even homes and office buildings that leave the lights on throughout the night without the use of shades or blinds.

Light pollution disrupts the natural sleep-wake cycle that repeats every 24 hours, known as the circadian rhythm. It also distorts natural rhythms in seasonal lighting that provide important cues to all life on Earth, for example, for some species, when to begin hibernating or migrating.

It also changes the time that plants and animals spend awake or asleep. And it changes the activities they typically carry out during waking hours.

Large moth with narrow, pointed wing and brown stripes hovering near yellow flowers.
A white-lined sphinx moth pollinating a shrub with bright yellow flowers. Image via Tom Koerner/ USFWS.

Nocturnal pollinators

The impacts of light on other species such as birds and sea turtles are better known. But few studies evaluated the interaction between insects, pollinators, plants and artificial light. Melissa Burns, western monarch coordinator for the U.S. Fish and Wildlife Service:

Although not well-studied, we are beginning to more clearly understand the impact light pollution has on insects and pollinators. This topic is emerging in more and more conversations.

The studies that have been conducted show artificial lighting can drastically affect the behavior of insects and pollinators, and therefore the ability of plants to produce fruit and reproduce.

In 2014, a group of scientists in the United Kingdom studied the effects of streetlamps on moths. The scientists found that 70% of the moths flew towards the streetlamps and away from flowering plants. This resulted in a reduction of plant pollination.

A separate study conducted in 2017 also found that nighttime pollinators were less likely to visit plants underneath artificial light, also reducing pollination and fruit produced by the plants. The researchers found that approximately 62% fewer insects visited the plants in a meadow illuminated at night with LED streetlamps than a meadow naturally lit by the moon.

A need to know more

Both studies show that the presence of artificial light at night deters pollinators from their nightly routine. Some nocturnal pollinators are attracted to and disoriented by artificial light, expending precious energy and distracting them from their nighttime routines and pollination duties. Others are deterred by well-lit areas. In both cases, the result is a disruption in nighttime pollination and fewer plants producing fruit and reproducing. Researchers are not exactly sure why this happens, but there are several theories. Burns explained:

Artificial lighting at night also increases a nocturnal pollinator’s risk of predation because they are easier to see. Their ability to see and avoid predators is also reduced by the lighting. So they may avoid it. This risk is thought to be one of the factors contributing to declines in nocturnal pollinators globally.

More research is needed to understand how exactly artificial lights impact plants and pollinators and the long-term implications.

Luckily, each of us can adjust how we use outdoor lighting through the tips below and help our backyard pollinators. These actions also have the added bonus of helping other species of wildlife, reducing energy use and costs and contributing towards a healthier future in the face of a changing climate.

How to dim the lights from your home

– Keep light indoors: close blinds or curtains drawn at night to keep the light inside.
– Color matters: use warmer colored light bulbs and minimize blue-violet light (light bulbs with a temperature of no more than 3000 kelvins).
– Use outdoor light where and when you need it: control your lighting through motion detectors, timers or dimmers. Use motion-triggered lights to address safety concerns.
– Keep light where you want it: properly shield all outdoor lights to eliminate light pollution drifting into the sky.
– Visit International Dark Sky Certified places (and Refuges!) to learn more about light pollution and experience the night sky! The U.S. Fish and Wildlife Service manages two internationally certified places: Valle de Oro National Wildlife Refuge in New Mexico is certified as an Urban Dark Sky Place and Lost Trail National Wildlife Refuge in Montana is certified as an International Dark Sky Sanctuary.
– Plant a moon garden for nighttime pollinators.

Dark blue orbital view of US with glowing yellow spots and streams especially in the east.
A map of the United States showing the extent of artificial lighting at night. Map via NASA Earth Observatory/ USFWS.

Bottom line: There are natural sources of skyglow, such as a full moon. But, increasingly, skyglow comes from anthropogenic (human-caused) sources. And scientists are learning that excess light at night is a form of pollution that can disrupt the natural rhythms of wildlife and plants. Tips for reducing skyglow in your home, here.


August 31, 2023
Human World

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