AMNA NAWAZ: Today marks the final day of Dark Sky Week, which is hailed as a global celebration of the night and a call for less light pollution.

In some cities internationally, local governments are trying to find a solution to lighting the night that can better serve critical wildlife ecosystems and humans alike.

Malcolm Brabant reports from Denmark.

MALCOLM BRABANT: It's dusk in Gladsaxe, a municipality north of Copenhagen that prides itself on combining urban growth with environmental initiatives.

Gladsaxe was the first Danish local authority to install red street lighting that helps reset the balance between human beings and the animal kingdom.

The council removed conventional white spectrum street lamps from this stretch of road next to a large bat colony in the trees.

Artificial white light is hugely disruptive for a broad range of creatures.

For example, bees get a form of jet lag, frogs lose their libido and bats find it difficult to catch food.

Red light enables bats to see in the dark, unlike white light, which blinds them.

The simple solution to restoring bats' night vision has been adopted in Metz in Eastern France, Worcestershire in the British midlands, Germany, the Netherlands, Belgium.

And it's spreading.

RUNE BRANDT HERMANSSON, Lighting Consultant: Every light source we put up changes some balances, moves things around, makes it easier for some animals to find a mate, get food, and makes it harder for someone else.

MALCOLM BRABANT: Rune Brandt Hermansson was one of the designers behind the red light project in Gladsaxe.

RUNE BRANDT HERMANSSON: We need to take care and try to change and affect our surroundings as little as possible.

And a lot of lighting is actually there for no one's sake.

I'm not an advocate that we should not have lighting for humans.

I'm an advocate that we should try and have as little lighting as we can, so we can offer more darkness for nature.

MALCOLM BRABANT: Biologists say that people need to recognize the importance of bats in the ecosystem.

They may resemble rats with wings, but they have a critical role to play in protecting human health.

MIKKEL STENER MOELLER: We underestimate the importance of bats.

MALCOLM BRABANT: Mikkel Stener Moeller is a senior biologist with a the Danish Sustainable Development Consultancy.

MIKKEL STENER MOELLER: Bats are predators and they eat half the weight in insects every night.

They're kind of a pest control and an important part of keeping insect populations in kind of a natural balance and check.

MALCOLM BRABANT: The consequence of bats failing to feast on insects is that farmers are forced to use chemical pesticides on their crops.

Studies have shown that the toxins can contribute to cancer and other diseases in humans.

MIKKEL STENER MOELLER: It's important to regulate how we affect the ecosystem, not only for the ecosystem itself, but for our health.

MALCOLM BRABANT: Stener Moeller blends his biological knowledge with the design skills of lighting consultant Lisa Dam Trapp to create the most efficient illumination for a client's parking lot next to a sensitive wildlife habitat.

LISA DAM TRAPP, Lighting Consultant: People are actually adapting to this new technology and this new type of light.

We have been used to having this very bright light during nights.

And we have to actually change our mind-set.

And people are, I think, really embracing this a lot.

People in Denmark really care about the nature.

If we can do something different, I think that people are really up for it.

MALCOLM BRABANT: Odense, Denmark's third largest city is the latest to install biodiversity lights.

This version, using orangey red lamps, becomes softer and warmer as the night darkens, aligning with the circadian rhythms or internal body clocks of nocturnal wildlife.

But as runner Michael Groenbaek explains, some people find the darker pathways intimidating.

MICHAEL GROENBAEK, Resident, Odense, Denmark (through translator): For those who have a fear of darkness, I think that this can feel unsafe.

Some people prefer more light.

Some don't.

It doesn't bother me.

MALCOLM BRABANT: Gladsaxe sees itself as a role model for other cities around the world.

Switching to red lamps has proved to be a cost-effective way of addressing light pollution.

The system uses less power and requires less maintenance than conventional street lighting.

Serdal Benli is Gladsaxe's mayor.

SERDAL BENLI, Mayor of Gladsaxe, Denmark (through translator): I hope that we can help inspire other municipalities to join the bandwagon here, because it is quite important that we think about sustainability, think about biodiversity all the way around, because that is what we owe to future generations.

We owe it to our planet and to those we share this planet with, namely, to all living beings on this planet.

MALCOLM BRABANT: And consultant Rune Brandt Hermansson predicts that improvements in lighting technology will contribute more to the harmonious coexistence of humans and the animal kingdom.

RUNE BRANDT HERMANSSON: We are at the brink of a lot of technological advancements that can actually make a difference without it having a negative impact on humans, because we shouldn't change society.

I mean, we need lighting to do what we do.

There's no reason for us not to have our light and for nature to have the darkness or their light.

MALCOLM BRABANT: Conventional lighting accounts for approximately 5 percent of all global carbon dioxide emissions and 15 percent of total global electricity consumption worldwide.

So, the experts say, switching to red street lights could contribute to slowing climate change, as well as helping bats to maintain a healthy insect diet.

For the "PBS News Hour," I'm Malcolm Brabant in Gladsaxe, Denmark.