Denmark is turning its streetlights red, and the reason will surprise you

In a suburb near Copenhagen, Denmark, familiar white streetlights are being replaced with red lighting on chosen roads. The adjustment is slight in scope but purposeful in intent. Officials claim it is intended to protect wildlife while keeping streets usable for people. Urban lighting has historically prioritised visibility and safety, often with little regard for environmental impact. This initiative represents a more gradual review of that strategy. It is based on research, local conditions, and overall sustainability goals. While the initiative is now limited to one region, it has sparked interest outside Denmark, as cities throughout the world grapple with similar problems regarding how to light streets without overwhelming the surrounding environment.The project is taking place in Gladsaxe, on the outskirts of Copenhagen. Red-toned lighting is replacing standard streetlights along parts of Frederiksborgvej near Skovbrynet. According to the press release from the Gladsaxe municipality, the area is known to host a local bat colony. Rather than turning lights off entirely, the municipality chose a colour that alters how light interacts with wildlife. The change is visible only at night and only along specific stretches of road.Bats were essential to the preparation. It has been demonstrated that artificial lighting impairs bats' capacity for movement, feeding, and navigation. The greatest effect is typically produced by short-wavelength light, such as that of blue, green, or white. Research from the Netherlands suggests that red light, which has longer wavelengths, may have less of an effect on bat behaviour. Furthermore, it is believed that bats are better suited to hunt insects. Local officials said that entirely shutting off the lights was not an option due to safety concerns. Red light was the least disruptive choice.While parts of the road now use red lighting, safety for drivers and cyclists remains a priority. At junctions and crossing points, warm white lights are still used. These are mounted on higher masts to improve visibility where it is most needed. The lighting design varies along the route, adjusting to how people and animals use different sections of the road. The aim is to avoid a one size fits all approach. Engineers monitored accident data, wildlife movement, and public feedback to refine illumination levels without compromising navigation, comfort, or environmental protection.Road engineer Jonas Jørgensen from Gladsaxe Municipality said the goal was to limit disturbance without reducing accessibility. He noted that complete darkness would be ideal for bats but not realistic for a public road. The solution, he said, reflects a balance between environmental care and everyday use. The project required careful planning rather than a simple switch.The lighting system was developed with professional lighting designers. They describe the project as an opportunity to challenge long-held assumptions about urban lighting. Philip Jelvard from Light Bureau said there would be an adjustment period for both people and bats. He added that the red light also carries symbolic weight, signalling that the area is environmentally sensitive.Gladsaxe was Denmark’s first municipality to formally align its strategy with the United Nations Sustainable Development Goals. Biodiversity protection is part of that framework. Mayor Trine Graese said the project shows how infrastructure can support both human needs and animal welfare. She described it as a practical example rather than a statement gesture.The red streetlights are currently limited to a certain route. There are no urgent plans to expand them throughout the city. Other urban planners are still keeping an eye on things. Gladsaxe provides a peaceful example as towns consider energy use, biodiversity loss, and nighttime design. It does not guarantee a solution for every street. It simply investigates if light can be used more sparingly and whether cities can learn to notice what has long been overlooked.