Iowa DOT replacing dozens of purple streetlights

CEDAR RAPIDS — The streetlights glowing purple and blue along the S-curve of downtown Cedar Rapids’ Interstate 380 aren’t a new design touch.

They are a result of deteriorated LED streetlights, causing the state’s transportation department to replace dozens of them across Iowa. The defective fixtures make up a small percentage of Acuity American Electric Lighting bulbs — which the state installed in 2018 — that were distributed nationally.

John Hart, director of the maintenance bureau at the Iowa Department of Transportation, said crews have changed 22 streetlight heads in the last two to three weeks across the state, and predicts to change at least 100 more in the near future.

“We want a bright light for safety, and for that light to be consistent and white, so we don’t change that,” he said. “We want it to be similar and consistent statewide.”

States such as Kentucky, Illinois, Kansas and Wisconsin also have reported thousands of blue-purple streetlights.

Hart said many transportation departments in the United States switched to LED’s after 2017, including Iowa, because they were more affordable and an environmentally conscious option. The purple-blue hue comes from deterioration of the LED streetlight head’s inside coating, Hart said.

“Once that coating comes off, the actual LED hue or blueness is showing through without that coating on,” he said.

Neil Egan, Acuity American Electric Lighting director of communications, said the phenomenon is called a spectral shift caused by phosphor displacement after years of installation.

“The light output is in no way harmful or unsafe,” Egan said. “As always, we stand behind the quality of our products, and we have been proactively working with customers who have experienced the issue to address any concerns.”

LED lights emit blue or UV light that is then covered by phosphors to convert the purple light to white light, according to the U.S. Office of Energy Efficiency and Renewable Energy.

Hart said that the streetlights have a five-year warranty, so the light head replacements are at no cost to the Iowa DOT.

“We’re going to continue to work on this so we can get back to our consistent lighting approach with our standard lighting and get these replaced on warranty,” he said.

The Iowa DOT lighting crews are seeing a large amount of the purple-blue streetlight heads in southeast Iowa, Hart said.

“For some reason, we had a particular area where we’ve had a stretch. … That’s primarily the area,” Hart said. He said the Iowa DOT is replacing the lights as soon as the crew sees one turn purple.

“The situation is evolving as crews look for the purple lights more aggressively,” he said. “We have other problems with lights going out, lights getting hit, and all of the above, so we are constantly maintaining and repairing the system.”

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