How Denmark's Red Streetlights Do A Lot More Than Save Energy

A quaint neighborhood north of Copenhagen, Denmark has adopted a radical tweak to its nighttime streetscape — red streetlights in select areas rather than the usual white streetlights. In the municipality of Gladsaxe, officials have been replacing traditional streetlights with red-spectrum LEDs. This change is rooted in real science and reflects a deeper shift in how cities may eventually consider environmentalism in their infrastructure.

Historically, most street lighting schemes equated brightness with safety — using white light to maximize visibility for drivers and pedestrians. Those same light wavelengths are increasingly recognized as harmful to nocturnal wildlife, particularly bats. 

Research demonstrates that light at night influences bat behavior in wavelength-specific ways, with longer-wavelength red light appearing to minimize behavioral disruption while still providing sufficient functional illumination for drivers. The Danish recognize bats' vital contirbution to mosquito control, and the red lightning represents an effort to reduce human-made interference in the behaviors bats rely on to survive. 

Red LEDs have specifically been installed on a stretch of Frederiksborgvej over four-tenths of a mile long. This road cuts through tree-lined corridors and a colony that's home to seven bat species. The goal is to balance roadway visibility for safety with a lightning approach that minimizes harm to the surrounding ecosystem.

The Gladsaxe project isn't just about light spectra; it's part of a larger reevaluation of how cities interact with the natural world — namely, the aspirations of the European Union-funded Lighting Metropolis – Green Mobility Program. The program aimed to implement LED lighting more swiftly across the Øresund Region of Northern Europe, and involved infrastructure in Denmark and Sweden between 2019 and 2022. 

Denmark's commitment to environmental integrity is no secret, with the nation going as far as to investigate BMW's sustainability claims a few years back. Since then, the EU has rolled back several high-profile environmental commitments, such as its 2035 internal combustion engine ban, and whether the environment is a priority for world leaders is questionable. But at the very least, these red lights are in the best interest of the bats.

Ultimately the project's success won't be judged by how the red lights look to residents, but by what the data reveals. Researchers in Gladsaxe are actively monitoring bat activity and traffic conditions along the red-lit corridor to evaluate how the lighting affects local wildife. Those findings will determine whether the approach meaningfully reduces disruption and its ability to be implemented across other cities in Denmark and beyond.