On a main road in Gladsaxe, a Copenhagen suburb, the glow is distinctly red. The change is not a design statement but a practical measure to reduce light pollution and protect a nearby bat colony. The project, led by AFRY Architects, is part of a broader European trend of using red LED streetlights to make urban infrastructure more wildlife-friendly.
Bats and the problem with white light
Research has long shown that artificial white light at night can disrupt nocturnal animals. For bats, which rely on darkness to hunt insects and avoid predators, white light can be particularly harmful. A landmark study by the Netherlands Institute of Ecology, published in 2017, measured for the first time how different light spectra affect bat activity. The five-year experiment, conducted at eight sites along forest edges in the Netherlands, found that slow-flying, light-shy bats such as Natterer's bat and the brown long-eared bat are significantly less active under white and green light. In contrast, red light had virtually no effect, with bats behaving as they would in complete darkness.
Lead researcher Kamiel Spoelstra explained: "We've found these bats to be equally active in red light and in darkness. White and green light, on the other hand, substantially reduce the bats' level of activity." The findings suggest that red lighting could be a viable compromise for areas where illumination is necessary but wildlife protection is a priority.
Red lights across Europe
In Gladsaxe, 31 one-metre-high bollards along a main road and cycle superhighway now emit a red glow. The spacing is deliberate: it allows light-shy species to cross without being exposed to predators, while still providing enough visibility for vehicles and cyclists. The project is part of a wider effort to reconcile urban development with environmental goals.
The Netherlands was an early adopter. In 2018, the town of Zuidhoek-Nieuwkoop became the world's first to install fauna-friendly red lighting. The UK followed in 2019, creating its first bat crossing with 60 metres of red lighting along the A4440 near Worcester's Warndon Woodlands nature reserve. These initiatives are part of a growing movement to rethink street lighting, which also includes efforts to make cities more walkable and reduce the dominance of cars.
Not all bats are alike
The 2017 study also revealed that different bat species respond differently to light. Agile flyers like the pipistrelle are not bothered by streetlights; in fact, they may benefit from the insects that gather around them. Larger species, such as the serotine bat and the lesser noctule, fly high enough to be unaffected. The main concern is for slower, more cautious species that are vulnerable to visual predators like owls.
Red lighting offers a practical solution because it holds up under real-world conditions. "It's entirely suitable for use on country roads," said Spoelstra. "This opens up possibilities for limiting the disruption caused by external, artificial lighting in natural areas, in situations where having light is considered desirable."
The shift to red lighting is not just about bats. It is part of a broader conversation about how cities can reduce their environmental footprint. As European cities tighten rules on everything from short-term rentals to e-scooters, lighting is emerging as another area where local governments can make a tangible difference. While red lights may not be suitable for every street, they offer a simple, low-cost way to protect biodiversity without compromising safety.
As more cities experiment with red lighting, the evidence base grows. The Gladsaxe project, like those in the Netherlands and the UK, will be monitored to assess its impact on bat populations. If successful, it could inspire similar measures across Europe, from the Baltic states to the Balkans. For now, the red glow is a small but visible sign of a changing approach to urban design—one that takes the needs of other species into account.
