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Why America's Streetlights Have Been Turning Purple
A manufacturing defect that would please Prince
Right around the time of the pandemic, people across America began noticing something unusual: Streetlights were turning purple. In at least 30 states, people started taking photos like these, typically posting them to social media with questions.
In this photo you can see that the effect isn't consistent across neighboring streetlamps.
Scientific American got to the bottom of what was happening. All of the streetlamps that turned purple were LED "upgrades" from sodium lamps. LEDs cannot produce truly white light, just red, green or blue. To compensate, manufacturers use blue LEDs coated with phosphor. This phosphor layer distorts the blue wavelengths to produce a light that appears white.
The phosphor layers in the affected lamps have been delaminating, yielding purple. In short, it's a manufacturing defect. American Electric Lighting, an Atlanta-based manufacturer that has federal contracts and makes (or at least assembles) their lights in America, is one of the suppliers that has acknowledged the malfunction. Other manufacturers have not been named.
AEL, for their part, has been stepping up and replacing the affected lamps.
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I discovered this defect a couple years ago when I started noticing purple lights all over Phoenix. I find it quite unpleasant on the eyes, but my 5 year old daughter loves the purple.
After a cursory search, I was unable to find any US or North American companies that manufacture LED chips. My guess is that an overwhelming percentage of LED chips for general lighting are manufactured in China. When our town made the switch to LED traffic lights, the green LEDs were not yet reliable. There were numerous failures leading to interesting abstract lighting designs. Eventually they were either replaced with whatever old technology was used or better green LEDs. The shorter the wavelength the harder it is to make. I used some of the first UV LED arrays (made by Phoseon in Oregon) to cure the polymer layer of a thin-film encapsulation for organic LEDs (OLEDs). They were a god-send and eliminated the massive heat load generated by mercury vapor bulb UV sources.