US Streetlights Are Turning Purple

Summary

American cities and towns started switching their streetlights from sodium lamps to LEDs about 15 years ago, which changed the color of many nighttime roads from yellowish orange to bright white. But lately an odd new nocturnal color has been spotted across the nation—and the globe. Anecdotal reports of purple-looking streetlights have been popping up since early 2021 in states including Florida, Utah, Texas and Massachusetts, as well as in Canada and Ireland.This phenomenon might seem weird but innocuous. After all, what harm could purple streetlights possibly do other than scare nearby residents as Halloween approaches? But it turns out that the hue of the light illuminating a roadway could affect how drivers and pedestrians perceive their surroundings as they make their way through the night. And that makes purple streetlights a potential safety hazard.How do white LED streetlights work?On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.Updating streetlights to use light-emitting diodes makes sense. LEDs are one of the most energy-efficient lighting technologies that currently exist, according to the U.S. Department of Energy. They also tend to be more durable and longer-lasting than other types of lighting while producing light that is comparable or better in quality.These diodes can emit light at a variety of wavelengths—but one color they do not produce naturally is white. So when you see white LEDs, such as those in streetlights, they are actually emanating some mixture of the colors red, green and blue (or red, yellow and blue), which together produce the appearance of white. There are two popular ways to create this illusion. One is to combine tiny LED lights that each emit red, green or blue into a single big device. The other is to use o...