The Royal Streetlamps, Explained – CleanTechnica

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There’s a street in El Paso where things are a little strange. Instead of a bright white LED light bathing Mesa Street like it used to, there’s a strange, hazy purple light coming from the bulbs above. When I first saw this, I assumed that it must be intentional. After all, there were so many bulbs all putting out that same royal purple color. Maybe it was better for light pollution? Maybe it attracted fewer insects? Or, was it a color for a nearby high school team? I made a few guesses and then drove on.

But, later, it became clear that this was hardly an isolate incident. LED streetlamps are turning the same strange purple color in a number of U.S. states, and it’s a little baffling. For some people, it’s fun. Car shows started happening in the “Purple Light Districts” and people got cool pictures of their cars. For other people, the lighting is not only annoying, but induces headaches and might even be making the streets less safe. For others, it’s conspiracy theory time.

But, thanks to an article I came across at The Autopian recently, the answer behind this baffling regal phenomenon is finally coming to light. It turns out that a big batch of LED street bulbs had a hidden defect. 

The problem with LEDs (light emitting diodes) is that you can’t really make them white. They pretty much need to be red, blue, or green (or some related shade). So, getting white light requires either putting all of the colors together in equal amounts (an expensive and complicated way to make a light), or you can put in one color and run the light through some filtering glass to change the color to white before it leaves the bulb. It turned out that the least expensive way to do this was with, you guessed it, purple or UV LEDs. The filter, made from a phosphor material, was supposed to last a long time and keep the output color white.

But, some of the filtering layers have worn out prematurely. The coating is flaking off and the purple light is increasingly coming through. The companies and scientists who study such things are baffled as to why. Manufacturers are selling replacement bulbs, but new batches are going bad more quickly than cities and states can replace them in many cases.

But, like the phenomenon of white dog poop in the 1980s, this purple lighting trend will not last forever. Governments are planning to replace the purple bulbs as soon as better replacements are available. So, our kids will probably have this strange tale to tell their kids about the time when street lights were purple.

One thing that won’t change (despite the rantings of a few weirdos who have my e-mail address) is the use of LEDs. While early LEDs are sometimes defective and do things like turn purple or flash when they fail, and some cars’ headlights are simply too bright (especially aftermarket LEDs for older vehicles), these are problems that are being solved and improved upon. The benefits of LEDs are here to stay, even if we’re experiencing some growing pains.

Featured image by the U.S. Department of Energy.