The Dark Side of Light

Like all mammals, bats are warm-blooded, give birth to live young, and produce milk to feed them. But bats can do something no other mammal can do—fly. “Bats’ ability to fly allows them to colonize lots of habitats,” says Frick. That includes cities.

Bats are able to navigate the cityscape just like they would in a natural setting, by using echolocation. They emit high-pitched sounds and listen for them to echo back (see Seeing With Sound). By doing this, they are able to zero in on objects they can’t spy with their eyes in the dark, such as tasty moths, and avoid collisions with things such as buildings. Contrary to popular belief, bats aren’t blind. Their sensitive eyes work particularly well in low light at dusk and dawn. But, like us, they can’t see well in pitch black.

Like all mammals, bats are warm-blooded. They give birth to live young and produce milk to feed them. But bats can fly. No other mammal can do that. “Bats’ ability to fly allows them to colonize lots of habitats,” says Frick. That includes cities.

Bats can find their way through a city just like they would in a natural setting. They use echolocation. They release high-pitched sounds and listen for them to echo back (see Seeing With Sound). That’s how they can find objects they can’t see with their eyes in the dark, such as tasty moths. That’s also how they avoid flying into things such as buildings. Many people think bats are blind, but they’re not. Their sensitive eyes work quite well in low light at dusk and dawn. But, like us, they can’t see well in pitch black.

People make up for our poor night vision (and the fact that we can’t echolocate) with the help of an important invention: the light bulb. At night, we just flip a switch to illuminate the world around us. This benefits our species, helping us feel safe and increasing the amount of time we have to work and play. Unfortunately, though, our lights aren’t so helpful for bats or other creatures—from insects and birds to turtles and frogs—whose survival depends on the dark (see Blinded by the Light).

“These animals’ lifestyles and breeding habits can be really disturbed by the lights people use,” says Clyde Porcella, a lighting educator at Access Fixtures, a company in  Massachusetts that develops wildlife-friendly light technologies. “Yes, people need light. But it’s important that we find ways to stop blasting it out into the world that we share with all living things.”

People have poor night vision and can’t echolocate. But we make up for that with the help of an important invention, the light bulb. At night, we just flip a switch to light up the world around us. Of course, this benefits our species. It helps us feel safe and gives us more time to work and play. But sadly, our lights aren’t so helpful for bats or other creatures who need the dark to survive. That includes some insects, birds, turtles, and frogs (see Blinded by the Light).

“These animals’ lifestyles and breeding habits can be really disturbed by the lights people use,” says Clyde Porcella. He’s a lighting educator at Access Fixtures. This company in Massachusetts develops wildlife-friendly light technologies. “Yes, people need light. But it’s important that we find ways to stop blasting it out into the world that we share with all living things.”

True darkness is getting harder to find on our planet. During the past century, electric lighting has made the nighttime sky 20 percent brighter. Recent estimates suggest that 99 percent of Americans and Europeans live under light-polluted skies (see Glowing World). In towns and cities, the glow from electric lighting can make it nearly impossible to see the stars. That’s bad news for stargazers and nocturnal creatures alike.

The type of artificial light flooding our planet is also an issue. The world over, individuals and communities are replacing old types of lights with newer light emitting diodes (LEDs). “LED technology has numerous benefits,” says Porcella, the lighting educator. “LED lights use far less electricity. And they generate light without generating heat. So they’re energy efficient.” Not wasting energy is good for the environment. But LEDs can have a downside.

True darkness is getting harder to find on our planet. The nighttime sky has become 20 percent brighter during the past century. That’s because of electric lighting. Recent reports suggest that 99 percent of Americans and Europeans live under light-polluted skies (see Glowing World). In towns and cities, electric lighting can make it nearly impossible to see the stars. That’s bad news for both stargazers and nocturnal creatures.

Another issue is the type of artificial light flooding our planet. People and communities around the world are replacing older lights with light emitting diodes (LEDs). “LED technology has numerous benefits,” says Porcella, the lighting educator. “LED lights use far less electricity. And they generate light without generating heat. So they’re energy efficient.” Not wasting energy is good for the environment. But LEDs can have a downside.

Wildlife scientists have noticed that certain colors of LED lights, like those with cool-white and bluish hues, seem to bother nocturnal animals. Warmer hues, though, don’t seem to affect wildlife at all (see Light-Pollution Solutions). “These warmer hues have what we call ‘a wildlife-friendly wavelength,’” Porcella explains. Visible light contains many wavelengths. Each wavelength—a measurement of the distance between a light wave’s peaks—corresponds to a different color of light. Wavelengths that produce a reddish tint, which people can see, seem to be invisible to nocturnal animals.

“Bats don’t see red light as particularly bright, if they even see it at all,” says Maurice Donners. He’s an engineer at Signify, the company formerly known as Philips Lighting, who helped invent new bat-friendly streetlights being used in the Netherlands. Because bats don’t perceive the redder light from Signify lamps, they don’t react to it. They follow their natural instincts when they emerge from their roosts at night. Light pollution doesn’t direct how and where they feed or which commuting routes they flap and flutter along.

Wildlife scientists have noticed a problem with certain colors of LED lights. Those with cool-white and bluish colors seem to bother nocturnal animals. But warmer hues don’t seem to affect wildlife (see Light-Pollution Solutions). “These warmer hues have what we call ‘a wildlife-friendly wavelength,’” Porcella explains. Wavelength is a measurement of the distance between a light wave’s peaks. Visible light contains many wavelengths. Each one produces a different color of light. People can see wavelengths with a reddish tint. But these seem to be invisible to nocturnal animals.

“Bats don’t see red light as particularly bright, if they even see it at all,” says Maurice Donners. He’s an engineer at Signify, the company formerly known as Philips Lighting. He helped invent new bat-friendly streetlights being used in the Netherlands. Bats don’t notice the redder light from the Signify lamps, so they don’t react to it. They just come out of their roosts at night and follow their natural instincts. Light pollution doesn’t direct how and where they feed. And it doesn’t control the routes they travel.