The Purple Street Lights Phenomenon

Across the United States and other parts of North America, streets are taking on a strange purple hue at night due to the failure of LED streetlights. This phenomenon has been observed in cities like Tampa, Vancouver, Wichita, Boston, and Albuquerque.

• The purple color is caused by the failure of the phosphor coating on LED streetlights.
• The phosphor coating is responsible for converting the blue light emitted by the LEDs into a white light suitable for street lighting.
• When the phosphor coating fails or delaminates, the blue light from the LEDs is no longer converted, resulting in a purple hue.

Understanding LED Lighting and Fluorescence

LED lighting technology relies on the principles of fluorescence and phosphorescence to produce high-quality white light. This section explores these concepts and their relation to LED lighting.

• Fluorescence is a phenomenon where materials absorb light, become excited, and then re-emit it at a longer wavelength.
• Phosphorescence is a closely related phenomenon that involves kicking an electron up to a different spin state, with the material continuing to glow for a short period after the excitation source is removed.
• Phosphor coatings on LED lights absorb a portion of the blue light emitted by the LEDs and re-emit it at longer wavelengths (red and green), producing a high-quality white light.

The Role of Acuity Brands in LED Streetlights

Acuity Brands, a major lighting manufacturer based in Atlanta, has played a significant role in the widespread adoption of LED streetlights across North America.

• Acuity Brands has acquired numerous lighting companies over the years, becoming a dominant player in the LED streetlighting market.
• Around 2017, Acuity Brands started manufacturing defective LED streetlights, where the phosphor coating fails after approximately five years.
• This defect has led to the widespread purple streetlight phenomenon observed in various cities.

Identifying and Replacing Defective LED Streetlights

Cities and utilities are facing challenges in identifying and replacing the defective LED streetlights from Acuity Brands.

• Acuity Brands offers a long warranty on their street lighting products, and they are sending contractors to replace the defective lights, but the process is slow and costly.
• Smart streetlighting solutions that monitor energy usage are unable to detect the non-electrical failure of the phosphor coating.
• Cities and utilities are relying on visual inspections and reports from residents to identify the affected lights.

LED Lighting Failures and Flashing Lights

In addition to the purple streetlight phenomenon, LED lighting can also experience other failure modes, such as flashing lights.

• Flashing LED lights are often caused by a failure in the constant current power supply (driver), which continuously cycles the light on and off.
• Common failure modes include shorted LED modules, current limit issues, and soft start feature malfunctions.
• Flashing LED lights can create a "silent rave" effect, similar to the cycling observed in aging gas discharge street lighting.

The Future of LED Lighting and Phosphor Technology

The issues surrounding LED lighting and phosphor coatings highlight the need for continued research and development in this field.

• Improving the durability and longevity of phosphor coatings is crucial to prevent premature failures and reduce maintenance costs.
• Alternative technologies, such as direct emission of white light from LEDs or the use of different phosphor materials, may be explored.
• Better quality control and manufacturing processes can help ensure consistent performance and reliability of LED lighting products.