Streetlights Are Turning Cities Purple

The sky over the city of Vancouver was the color of a television tuned to a Prince concert.

OK, maybe not the whole sky. But enough of it that people noticed. A bunch of streetlights — a few hundred out of thousands — had suddenly changed. What had been moonshine white was now blue, or purple, or even violet. They weren’t any less bright, objectively speaking. But purple doesn’t exactly illuminate a sidewalk the way white does. The spectrum of Vancouver had taken a hard left turn. It didn’t look bad. It wasn’t unsafe, particularly. It was just weird.

So people placed worried calls to the city. And after all the hue and cry, Vancouver rolled out the utility trucks and set out to replace the chromatic aberrations — even though the lights were still pretty new. Like most other cities, Vancouver has spent the past few years switching from old sodium-vapor streetlights to LEDs. The new bulbs, basically arrays of computer chips that convert electricity to light, are cheaper, less power-hungry, and longer-lasting. LED streetlights are supposed to shine for the better part of a decade.

Unless they don’t. Because the Great Purpling didn’t start — or end — in Vancouver. Reports stretch back to 2020 and across the hemisphere — WisconsinNorth CarolinaFloridaNew MexicoCalifornia, even Ireland. “It’s something we began seeing about two years ago,” says Jeff Brooks, a representative for Duke Power, which is responsible for streetlights across the Carolinas and parts of Florida and the Midwest. “I’ve had people call and ask if this was because it’s Halloween, or because their football team in that area wears purple.” 

It isn’t ghost- or football-related. And it isn’t some grand conspiracy, though lots of people saw in the synthetic twilight the effects of 5G radiation or government surveillance, a sign of the times. There’s nothing shady going on here. But still: Streetlights aren’t supposed to spontaneously change color.

So I did a little digging. The mystery of the purple lights appears to be both more mundane and more worrisome than anyone has realized — a mood-indigo check-engine light on the entire infrastructure of modernity. When LED streetlights start changing color for no apparent reason, it’s a visual cue that we might need to rethink, just a bit, how we build the future.

Might makes light

In some ways, you could represent the whole idea of modern human society with a light bulb turning on above our heads. Few technologies have been as critical to shaping the world as we know it. For 300 years of human history, from 1500 to 1800, the cost of lighting a light — any kind, from candle to whale oil to coal — stayed pretty much the same. But in about 1800, the price started to plummet dramatically.

Cities of the Industrial Revolution were first illuminated by gas lamps — their mantles, the part that contained the gas’ bright flame, were the first wide-scale use of the same rare-earth metals now so critical to batteries. A century or so later, electricity became dominant, both indoors and as lights for city streets. First it was arc lights, then incandescent bulbs, neon, fluorescent tubes, mercury vapor, sodium vapor. For the past few years, LEDs have been the hot new thing, in part because they don’t get hot. They turn electricity into light directly — no intermediate steps, just a straight electron-to-photon swap: Zap! Very economical and climate-friendly. Today they’re a $20-billion-a-year business.

By the late 2000s, cities around the world were swapping their legacy lights for the modern, higher-tech LEDs. They were, broadly, white lights. But anyone who’s ever painted a bathroom knows that not all whites are the same. For technical reasons derived from quantum theory and the quirky psychophysics of our eyes and brains, scientists measure the color of white light in kelvins, or “color temperature.” Higher numbers are bluer; lower are yellower and redder. Lots of cities settled on 4,000 K, the lunar glow of high-end sports-car headlights — and, not coincidentally, one of the easiest and therefore cheapest white LEDs to manufacture. 

It was a startling switch from the more romantic, orange glow of sodium vapor. Less Paris by moonlight, more Porsche on the Autobahn. “The introduction of every new lighting technology caused a lot of consternation until people got used to it,” says Sandy Isenstadt, an art and architecture historian at the University of Delaware. “It’s often around color, sometimes simply around brightness. For that matter, even the introduction of gaslight caused a lot of concern.”

Still, most of us got used to the new bright white regime. And then it turned purple.

Why Faulty Streetlights Are Turning Cities Purple — and Why It’s Worrisome

Why Faulty Streetlights Are Turning Cities Purple — and Why It’s Worrisome
%d bloggers like this: