If you care about living things, turn off your lights at night

Many birds like Sandhill Cranes migrate during the night, navigating with the help of stars.
Rick Spitzer/Courtesy photo

When most people think about pollution they think about air, land, and water pollution. Types of pollution might include carbon monoxide, sulfur dioxide, nitrogen dioxide, ozone, hydrocarbons, thermal, radiation, plastics, acid rain, particulates, industrial waste, oil spills, smog, municipal solid waste, pesticides, litter, and a lot more.

How many times is there a discussion about light pollution?

For millions of years, the natural world adapted to the daily cycles of light and dark, as well as the yearly cycles of seasons. And then along came humans. Humans figured out a way to create artificial light. The human ability to generate light has produced many benefits for humans, but it has also caused many problems for other living things in the natural world.

Light pollution is the extraneous light in the night sky. It affects more than 80% of the world’s population. Light-polluted skies affect the majority of people in the U.S. and Europe. Most of the people in the world cannot see the Milky Way with the naked eye.

Light has a huge impact on our lives. Daily changes of light caused by the Earth’s rotation has an influence on our daily lives. Light has biological and psychological effects that can impact us as humans. Light, or lack of it, as well as color and brightness, can change our sleep cycles, mood, and mental acuteness.

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20% of the people in the world cannot see the Milky Way with the naked eye. Many of us can see it from our homes.
Rick Spitzer/Courtesy photo

Do we understand what impact light has on animals, or plants, or even microbes? Scientists are beginning to discover that light has a greater impact than they ever realized.

What can you do?
  • Turn off unnecessary outdoor lights at night
  • Use dimmers, timers, and motion detectors for lights. That will also save energy
  • Close curtains and blinds and turn off unnecessary interior lights at night
  • Use appropriate light shields to direct all lighting only to where it is needed
  • Keep lighting close to the ground and pointed down
  • Use amber LED bulbs or low-pressure sodium lights
  • Avoid blue light (short wavelength lights) in outdoor lighting fixtures
  • Find out how you can help make your school, office, and home Bird-Friendly
  • Discuss light pollution with family, friends, and government officials

The 24-hour cycle of light and dark, called circadian rhythms, causes physical, mental, and behavioral changes. The world’s flora and fauna have adapted to the natural rhythm of day and night.
Plants have biological clocks that allow them to respond to changes in light and the corresponding change in temperature.

Plants close flowers and change the positions of leaves at night. The growth rate of most plants is impacted by that change of light. Scientists have discovered that light pollution is affecting how some plants grow. It changes their seasonal rhythms and the ability to sense and react to light. That may have an impact on plants, their growth and their relationship with insects that pollinate them.

Broadtailed hummingbirds may be tricked by light pollution and may arrive before the flowers they require have bloomed.
Rick Spitzer/Courtesy photo

Daphnia are small aquatic crustaceans often called water fleas. Darkness triggers the movement to the surface where they eat the surface algae. Light pollution in some lakes prevents the movement of Daphnia to the surface at night. As a result, they do not eat the surface algae — and that leads to algal blooms that can change the taste and odor of public water supplies and produce toxins that can impact the health of humans, fish, mammals, and birds. As algal blooms decay, they use up oxygen in the water that can kill fish and other aquatic organisms.

Many creatures evolved to use the predictability of lightness and darkness for reproduction, feeding, rest, and protection from predation.

How light pollution impacts insects

Nighttime light pollution can interfere with the ability of monarch butterflies to navigate from Canada to Mexico and back during their multi-generational migration.

Scientists have found that light pollution may be one of the leading causes of insect decline. Nocturnal insects like fireflies and moths are in decline. Fireflies use bioluminescence to communicate and attract mates. Light pollution makes it difficult for female fireflies to differentiate between male fireflies and artificial lights.

Monarch butterflies navigate by the stars and may be losing their way.
Rick Spitzer/Courtesy photo

Moths normally use a fixed angle on a distant source of light like the moon to fly in a straight line. When moths fixate on close light sources they do not orient correctly and that causes erratic flight patterns.

Artificial light also affects aquatic insects. Some larval aquatic insects including mayflies, damselflies, dragonflies, caddisflies, and stoneflies detach themselves from rocks during the dark of night and float safely downstream. The fish cannot see the insects floating above them in the darkness. Artificial overhead light makes silhouettes of the insects and that makes it easier for fish to find and eat those insects.

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The earth’s revolution around the sun and the axis of rotation creates the four seasons. That has a lot to do with what we do in our daily activities, the foods we eat, the clothes we wear, and the sports we enjoy.

Light pollution disrupts the natural cycles and the “biological clock” of nocturnal wildlife by threatening the integrity of the night sky.

How light pollution impacts mammals

Many mammals are nocturnal, they are active at night. Lights at night may alter their day/night activity that makes it difficult and dangerous to be outside to find food. That creates a unique form of habitat loss. It may also interfere with good health, growth, and reproductive cycles. That light also makes it difficult to avoid predators. The light may attract predators, like coyotes and foxes, because it makes it easier for them to see their prey.

The color of stars is really incredible in this long exposure time. In polluted areas the ones that can be seen may all appear white.
Rick Spitzer/Courtesy photo

Migration is also impacted by light pollution. Animals that are triggered by light to start their journey may leave or arrive at a different point in the year and have problems locating food and other resources along the way or when they arrive.

Scientists believe that whales, and many other animals, might know the direction for migration based on the stars as reference points.

They do know that it is true for birds. Many birds migrate at night, some move from the Northern to the Southern Hemisphere and back each year. Their migrations are often triggered by the amount of light, but that is being changed by light pollution. 

But how do we know that the stars help them find their way? Researchers used captive birds inside a planetarium and would flip the direction of north and sometimes turn off the “stars” altogether. When they did that, the birds would change direction based on the appearance or lack of “stars in the sky.”

Nighttime lighting may interfere with that migratory activity. Many birds migrate at night. Light pollution contributes to the death of millions of migratory birds each year. They may start the migration and end it in areas with little light pollution, but they may be required to fly over areas with significant light pollution. During migration, low-flying birds may become confused, and circle illuminated areas risking exhaustion, predation, and fatal collision with buildings.

Many thousands of birds, like these sandhill cranes near Monte Vista, navigate by starlight during their migrations.
Rick Spitzer/Courtesy photo

Light pollution and its impact on migratory birds was the focus of World Migratory Bird Day in 2022. The theme that year was “Dim the Lights for Birds at Night.”

All of the towns along I-70 in Eagle County emit a lot of light into the night sky. A short trip from these towns will take you to some dark skies. Allow about 10 minutes for your eyes to adjust and you can see the Milky Way and make out the smudge of the Andromeda Galaxy in your view.

There are 10 International Dark Sky Parks and five International Dark Sky Communities in Colorado. We are not in one of those communities but we are in an area with outstanding stargazing opportunities.

A short trip away from town lights reveals an incredible night sky.
Rick Spitzer/Courtesy photo

What is a Dark Sky? The International Dark Sky Places Program has a scientific definition for a dark sky site with the purpose of restoring the nighttime environment and protecting communities from the harmful effects of light pollution. Their goal is to encourage communities, parks and protected areas to have lighting policies to protect dark sites. They want to ensure that everyone will have the opportunity to enjoy our stars and night skies. Any populated areas may apply to be “recognized as an International Dark Sky Community, provided there exists evidence of ‘exceptional dedication’ to the dark-sky cause.”

Rick Spitzer is a renowned wildlife photographer and longtime local who lives in Wildridge. The Eagle County Community Wildlife Roundtable is a collaborative partnership with the White River National Forest, Colorado Parks and Wildlife, Bureau of Land Management, local government entities, community members and citizen scientists. The purpose of the Eagle County Community Wildlife Roundtable is to gather a group of diverse stakeholders in the valley to understand and address issues facing wildlife populations.

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