Photo of bats flying through the night air over trees and cities
NOIRLab/NSF/AURA, P. Marenfeld (Background); Tom Vezo/Minden Pictures (Top Bat); Michael Durham/Minden Pictures (Bottom Bat)

Saving the Night

The darkness is key to the survival of bats and many other animals. How can we keep it from disappearing?

By Stephanie Drimmer
From the March/April 2024 Issue

Learning Objective: Students will explain problems caused by light pollution and design a solution.

Lexile: 790L; 510L
Other Focus Areas: Ecosystems, Measurement & Data
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The sun has set and the moon glows. As you pull up your covers and begin to nod off to sleep, there’s a creature outside your window doing just the opposite. An owl swivels its head, listening for prey. It’s alert and refreshed from a day’s rest.

It’s not alone. Many other animals are just waking up. A fox creeps on silent paws. Bats take flight in a whoosh of wings. Moths and crickets emerge from bushes and trees. These are nocturnal animals, and they thrive in the darkness. In fact, they couldn’t survive without it!

But this darkness is disappearing. Artificial light—light produced by humans—blazes from sources like streetlamps, billboards, and security lights. As a result, much of our planet is never completely dark at night.

In fact, the planet is getting brighter all the time. One study found that the night sky has been doubling in brightness every eight years! This light pollution is harming animals that are active at night.

The sun has set. The moon glows. You pull up your covers. You begin to fall asleep. But there’s an animal outside your window. It’s not sleepy at all. The owl turns its head. It’s listening for prey. It’s been resting all day. So it’s wide awake.

It’s not alone. Many animals are just waking up. A fox walks on quiet paws. Bats take flight. Moths and crickets come out. These are nocturnal animals. They love the dark. In fact, they couldn’t survive without it!

But this darkness is fading. That’s because of artificial light. It’s light made by humans. It comes from streetlamps, billboards, and security lights. Much of our planet is never totally dark at night as a result.

The planet is getting brighter all the time. Here’s what one study found. The night sky has been doubling in brightness. That’s happening every eight years! The result is light pollution. It’s hurting animals that are active at night.

Bright Idea?

Artificial light hasn’t been around very long. About 150 years ago, the light bulb was invented. It changed the world forever. Thanks to electric light, people could see well after the sun went down. That allowed them to easily work, travel, and play at night.   

Some artificial light is needed for human safety. Lights along streets help people drive more safely at night. But many artificial lights are not necessary. For instance, billboards and stadiums often have lights that stay on all night long.

Cities produce so much light that the stars become hard to see. That happens when light reflects off dust and water particles in the air, causing the night sky to glow.

Most living things are adapted to live in a world with a daily pattern of light and dark. Large amounts of light at night harms them.

“In just the past few decades, humans have created an enormous amount of light at night,” says Franz Hölker. He’s a scientist who studies the effects of light pollution. “Living things are not prepared for that.”

Artificial light hasn’t been around very long. The light bulb was invented about 150 years ago. It changed the world forever. People could now see well after the sun went down. It allowed them to do more at night. They could easily work, travel, and play.  

Some artificial light is needed. Streetlights help at night. They allow people to drive more safely. But many artificial lights aren’t needed. For example, billboards and stadiums have bright lights. They often stay on all night long.

Cities give off a lot of light. That can make it hard to see the stars. That’s because of dust and water in the air. Light reflects off these particles. It causes the night sky to glow.

Our world has a daily pattern. Most living things need periods of both light and dark. Large amounts of light at night harms them.

“In just the past few decades, humans have created an enormous amount of light at night,” says Franz Hölker. He’s a scientist. He studies light pollution. “Living things are not prepared for that.”

Night Light

It’s the middle of the night, and a bat is on the hunt. It gobbles up the mosquitoes in a clearing, then begins to soar across a road—but stops. For the bat, the streetlights act like a roadblock.

Bats have eyes that can see in near darkness. So even small amounts of light bothers them and changes their behavior. Some types of bats avoid areas that are lit up at night. As a result, they may not be able to hunt enough to survive. Other bat species are drawn to streetlights, making them vulnerable to predators like owls. Bats play an important role in nature. Without them, the population of mosquitoes and other pests could grow out of control.

Artificial light puts certain insects, like moths, in danger. Many insects use light from stars to know where they are. Artificial light makes them lose their way. That’s why you see so many bugs buzzing near streetlights at night. There they become easy prey for certain predators like spiders. “Spiders use streetlights like a buffet,” says Hölker.

That’s good for the spiders, but birds and other animals depend on those insects as a food source. So if those insects disappear, other animals that eat them can go hungry.

Light pollution harms other animals too. (See Lost in the Light.) When baby turtles hatch on beaches, they use the light of the moon to find the ocean. Artificial lights lead them off their path. Lost hatchlings are at risk of threats like being run over by cars. Light pollution has also caused tree frogs to silence their mating calls and salmon to swim in the wrong direction!

It’s the middle of the night. A bat is on the hunt. It eats up mosquitoes in a clearing. Then it goes to soar across a road. It stops. There are streetlights. They act like a roadblock for the bat.

Bats’ eyes can see in near darkness. So even small amounts of light bother them. It changes how they act. Some bats avoid areas lit up at night. They may not be able to hunt enough. They can’t survive as a result. Other bat species are drawn to streetlights. That makes it easier for predators like owls to spot them. Bats play a big role in nature. They get rid of mosquitoes and other pests. Their numbers would grow out of control without bats.

Artificial light puts certain insects in danger. Moths use light from stars to know where they are. Artificial light makes them lose their way. That’s why so many bugs buzz near streetlights at night. That makes them easy prey for predators like spiders. “Spiders use streetlights like a buffet,” says Hölker.

That’s good for the spiders. But birds and other animals rely on those insects. They’re a food source. Fewer insects mean those animals may go hungry.

Light pollution harms other animals too. (See Lost in the Light.) Baby turtles hatch on beaches. They use the light of the moon to find the ocean. Artificial lights lead them off their path. Lost hatchlings face many threats. They may get run over by cars. Light pollution has affected tree frogs. It causes them to silence their mating calls. And it’s caused salmon to swim in the wrong direction!

Turn It Off

How can humans help cut down on light pollution? Some communities are taking important steps. Many beach towns in Mexico, Australia, and other countries have banned artificial lights during sea turtle hatching season. The ban has had a big effect. Some beaches found that all of their baby turtles headed toward the sea. Not one hatchling got lost!

Laws can help, but there are other steps communities can take right now, says Hölker. Streetlights should be as dim as possible and designed to direct light to the ground. A color swap can help too. Artificial light that’s orange or red in color bothers living things less than lights with a blue tint.

With just a few simple adjustments, people can help bring back the darkness around their homes and neighborhoods. (See Dark-Boosting Tips) “It’s easy to reduce light pollution,” says Hölker. “Anyone can do it!”

How can humans help lessen light pollution? People are finding ways to take action. Beach towns in several countries are turning off artificial lights. They do this during sea turtle hatching season. The ban has had a big effect. Some beaches found that all their baby turtles headed toward the sea. Not one hatchling got lost!

Laws can help. But there are other steps, says Hölker. And people can take them right now. Streetlights should be as dim as possible. And they should direct light to the ground. A color swap can help too. Artificial light that’s orange or red in color is better. It bothers living things less than lights with a blue tint.

It only takes a few simple changes. People can help bring back the darkness to the places where they live. (See Dark-Boosting Tips.) “It’s easy to reduce light pollution,” says Hölker. “Anyone can do it!”

video (1)
Activities (4) Download Answer Key
Quizzes (1)
Step-by-Step Lesson Plan

1. PREPARE TO READ (10 minutes)
Watch a video and identify natural and artificial light sources.

  • Ask: What light sources are we using right now? (e.g., sunlight coming through a window, overhead lights on the ceiling) Which light sources are natural and which are artificial, or human-made?
  • Show the “What You Need to Know About Light” video. Have students share one thing they learned.
  • Ask: How are artificial lights helpful to people? (e.g., They make the roads safer.) How might a bright light affect you when you’re trying to sleep? How do you think artificial lights might affect animals? Why?

2. READ AND Evaluate (20 minutes)
Read the article and think critically about local lighting sources.

  • Preview the map on page 25 and find the approximate location of your state. How does the light in your state compare with other parts of the U.S. and other parts of the world? Read the article aloud, pausing to note key ideas.
  • Ask: What kinds of lights do you see in your neighborhood after dark? (e.g., car headlights, streetlights, lights shining through windows, decorative outdoor lights) What about when you’re on a highway or in a shopping area? (e.g., illuminated signs and billboards) Which of these lights are absolutely necessary? (e.g., safety features like car headlights) Which could be shut off at a certain time? (e.g., billboard signs or decorative lights) What changes could be made? (e.g., Use dimmer lights, light fixtures that direct light to the ground, or bulbs that produce red or orange light.)
  • Have students use the article as a reference to complete the Quick Quiz. Reconvene to discuss their answers.

3. RESPOND TO READING (45 minutes)
Design and test a nature-friendly sidewalk light.

  • Set up for the Design a Sidewalk Light activity: To save time, you can prepunch holes in paper (step 3C) and precut strips of paper (step 3D) for students. If possible, dim the classroom’s lights a little so it’s light enough to read and write but dark enough to easily see light from flashlights.
  • Have students work in pairs or small groups. You may need to work through steps 1-3 as a class, then discuss the criteria, constraints, and design process (steps 4-7) before having students work in their small groups.

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