Ask Bungalower: What's up with all the purple street lights?
Jun 27, 2023
“Hey, guys. I’m wondering why I’m seeing so many purple street lights around town. At first I thought it had something to do with Orlando City, but then it wouldn’t be all of the lights on the street, just some of them. What’s up with that?”
One of the most significant advancements in outdoor lighting has been the widespread adoption of LED streetlights. These energy-efficient alternatives to traditional street lighting have gained popularity due to their longevity (an estimated 10 years per bulb), brightness, and reduced energy consumption, which translates to greater savings for municipalities.
However, in recent years, an unusual phenomenon has been observed in some LED streetlights—they are turning purple. LEDs, or Light-emitting diodes, produce light through a process called electroluminescence, where an electric current passes through a semiconductor, causing it to emit photons. The color of the emitted light depends on the materials used in the semiconductor.
One popular method used to create white light in LEDs is phosphor conversion. Blue LEDs, which are commonly used in lighting applications, have a yellow phosphor coating that absorbs some of the blue light and emits yellow light in return. The combination of blue and yellow light appears as white light to the human eye. However, when the phosphor degrades or the balance between blue and yellow light shifts, the result can be a purplish hue.
Since LED streetlights are exposed to various environmental factors such as temperature fluctuations, humidity, and exposure to UV radiation, (especially in Florida), these factors can accelerate the aging process of the phosphor coating, leading to color shifts over time. The degradation of the phosphor coating, combined with the dominant blue light emitted by LEDs, can result in a perceptible purple tint.
The phenomenon has been called the “Great Purpling” by media outlets across the country, and while it’s a relatively simple process to replace the lights, it’s still pretty expensive. And while the future is hopefully still full of energy-efficient street lighting, it may just have to be purple for a while as we ride out whether it’s better to squeeze a few more years out of those bulbs or swap them out. So don’t expect that purple to go away any time soon.
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Editor in Chief of Bungalower.com More by Brendan O'Connor Great Purpling