Why are the street lights a purple color?
Photo Credit: TMJ4 - Milwaukee, WI
Have you noticed a handful of street lights around your city with a purplish hue or color? You’re not alone and it is actually happening nationwide!
According to the Saint Paul Public Works Department, and several other public works departments across the country, the purple-colored lights are due to a manufacturer’s defect and failure with the Autobahn series LED “cobra style” street lights from the company American Electric Lighting (AEL) that were installed across the country between 2017 and 2019. In a blog article by Sam Finn on the site Night Sky Santa Fe, about six months ago over a dozen cities all across the country were reporting these issues with most of these issues occurring about 1-2 years after their installation.
What is causing the failure?
The way most LED streetlights work is by emitting a singular pure blue (blue-violet) LED light. In order to make these LED lights appear white, which is what we normally see, they cover the LED with a lens made of red and yellow phosphors (chemicals) that absorbs some of the blue color. The light that is emitted is then more in the red, orange, and yellow color spectrum which appears more white. The amount and thickness of phosphors used can determine the color temperature, for example, cool white, warm light, etc.
Now that we understand how LED lights work, why are these failing? Well, in short, the yellow film phosphors that are being used on these lights are actually burning off, causing more of an indigo LED color to come through which is leading to that intense blue-purple color we are seeing in some of the street lights across several cities.
What do I do if I see a purple street light?
The answer to this question really depends on what your local city is doing to resolve the problem. If you are in the city of Saint Paul, Minnesota, or Upstate, South Carolina local public works departments want you to call and report the light pole number to them so they can come out to replace the bulbs as they pop up. Other cities, like Milwaukee, Wisconsin, are in talks with the manufacturer to get them replaced.
If you are in fact in the city of Saint Paul, Minnesota, the local public works lighting division is 651-266-9777. They ask you please report the number on the light pole and its location to that number.
Have you seen purple lights in your city? Let us know!
Story Sources:
St Paul Public Works Department