With all of the chaos and unprecedented events of recent years, there’s a sort of collective feeling that unbelievable things could happen and it wouldn’t be all that surprising. As the phenomenon of otherworldly purple streetlights spans across the country, you’d be forgiven if you fell for any of the wild rumors about what’s causing it. The real cause is quite simple, actually: it’s a manufacturing defect that appears to affect a popular government contractor’s product.
For the young’uns who don’t remember this, streetlights used to emit a more yellowish orange light because they were a different type of bulb called sodium vapor lamps. Those lamps required more energy to operate, they created a lot of heat in the process, and their yellowish light (like that on old French cars) cut through fog better than white light. But the LED technology that replaced sodium vapor lamps does a better job of emulating sunlight, even though most LED headlight upgrades don’t really work.
LED streetlights also require less energy to operate, so as LED technology came more into the mainstream, cities decided to replace the old power-hungry sodium vapor lamps with efficient LED streetlights. Here’s why those LED streetlights turn purple.
Most white LEDs use a mixture of the full color spectrum
There is no such thing as a white LED — there are only red, green, and blue LEDs. Much like your computer screen or phone screen, LEDs create white light by mixing equal parts of each color. You know how doctors recommend against looking at screens before bed because of the blue light those screens emit? Blue light boosts alertness and helps memory and brain function, so it’s not great if you’re trying to wind down for bed, but it’s great for facilitating safe roads even at night time. To simplify the technology and keep costs down, most LED streetlights actually use blue lights viewed through a laminated yellowish filter made of phosphor and silicon that turns it into white light.
According to The Drive, two popular LED streetlight manufacturers, American Electric Lighting and Acuity Brand Lighting, are responsible for tens of thousands of defective streetlights across multiple states. Over the course of years, The Drive says, the laminated filters that cause the blue LED lights to emit white light have delaminated, cracked, or failed completely. When the yellow filter completely fails, the streetlight shines blue, but when it partially fails, the blue light interacts with the remaining yellow filter, causing purple streetlights. USA Today interviewed Peter Palomaki, an optics expert and chief scientist with Palomaki Consulting in Massachusetts, who said, “It’s not the phosphor itself that’s failing but the binder that’s attaching it to the LED, probably the silicon.”
The rapid expansion of energy-efficient technologies and poor quality control led to the issue
The occurrence of once-white streetlights suddenly shining purple begun around 2021, and in 2024, the LED Systems Reliability Consortium researched the problem. The group said most of the faulty LED streetlights it looked at were installed in the late 2010s. USA Today said the lights have warranties that generally last five to seven years, and an analysis of Acuity’s finances by the trade publication Inside Lighting shows that the company’s recall expenses rose from $32.3 million in 2021 to $47 million in 2022, and to $52.4 million in 2023. Palomaki said the failure of the lights appears to be environment-dependent, varying based on light, heat, and moisture.
The purple streetlights are neither black lights, nor are they emitting ultraviolet light, or any other conspiracy theory. They’re simply defective LEDs. The issue isn’t dangerous, but it can be disorienting for some people, especially when several streetlights are afflicted with the same problem, creating a very eerie, dystopian feeling at night. If streetlights in your area are affected by this issue, contact your local authorities to report the problem.