A perple streetlight is seen near the 400 block of North 15th Street in Milwaukee on Friday, July 2,2021. Many resident have noticed purple-hued streetlight on the interstate throughout the Milwaukee area. There is a  technical glitch in the LED bulbs installed by the state Department of Transportation roughly three years ago, and they will be replaced. Angela Peterson

The purple streetlights are back in the Milwaukee area, or may have never left after appearing on highways the last few years.

The Wisconsin Department of Transportation originally predicted in 2023 that fewer than 100 were left in the state and they'd soon be replaced, but an agency spokesperson said Thursday that "additional failures occurred in summer of 2023, which was more than anticipated."

The DOT installed a batch of LED lights in 2018, mostly in the southeast region. At least 300 lights began changing color from white to purple. The effect would lead to interstates being lit purple at night where these lights were highly concentrated.

When the DOT announced it was removing and replacing the lights, a number of people reached out to the Journal Sentinel, saying they preferred the lighting scheme. Some readers said it was easier on their eyes late at night while others thought purple was cooler than white.

"SAVE THE PURPLE LIGHTS!" one reader texted.

At the time, a spokesperson with the DOT said, "We are not going to a purple-hued street lighting plan. ... I didn't imagine that anybody was going to become that attached to them." The department added that bright white lights are necessary to safely light the interstates.

According to the DOT, the reason the light-emitting diode (LED) lights transitioned from white to purple has to do with a phosphor coating around individual diodes. The coating is placed there because LED lights for highways employ a blue LED naturally and the coating is used to diffuse the blue light to white.

The phosphor coating has been peeling off exposing the LED's blue color. The issue causes the lights to transition from white to purple over time. According to the manufacturer, the bonding of the coating is failing.

Ram Seshadri, a materials science professor at the University of California, Santa Barbara, told Scientific American that the phosphor technique is sound. "We’ve had LED lighting on the street for ... years, and there’s [been] no problem,” he said. Wisconsin transitioned to LED lights about 10 years ago.

The coating could be peeling due to heat buildup inside the light fixture because of constant operation, vibrations from passing cars or even gravity tugging downward on the phosphor layer, according to experts who spoke to Scientific American.

The manufacturer that supplied the faulty lights in the Milwaukee area is American Electric Lighting, a subsidiary of Acuity Brands Lighting. The DOT said in 2023 that American Electric Lighting paid all costs for the replacement of the faulty lights, including materials, labor and traffic control per product warranty.

DOT spokesperson Dan Sellers said Thursday that American Electric continues to covers costs as more purple streetlights appear.

Sellers said work will begin in March to replace the streetlights and is expected to be done by the end of the year.

Purple streetlights have appeared in a number of different municipalities in Wisconsin, including in Oshkosh, Wausau and Door County, and across the U.S., in Kansas, South Carolina, Illinois, Florida, Utah, Texas and Massachusetts.

 

TrendForce 2024 Global LED Lighting Market Analysis
Release Date: 01 February / 31 July 2024
Language: Traditional Chinese / English
File format: PDF and EXCEL
Number of pages: 100 (in each publication)