Purple skies at night? As some Elk Grove street lamps change color, city says it has a fix

The purple light beaming from some Elk Grove street lamps is the result of faulty LED chips, city officials say.

About 50 of Elk Grove’s nearly 15,000 street lamps have the defect, said Elk Grove deputy public works director Sean Gallagher on Monday, and are limited to the city’s “cobra head”-style streetlights. About 3,000 of the city’s LED lights are of the “cobra head” variety, Gallagher said.

The lamps’ odd glow has caused a stir on local social media, but Gallagher says crews are getting a handle on the issue after a nighttime, city-wide sweep last week to find the faulty lamps. Elk Grove’s street lights, all 14,649 of them, are light-emitting diodes.

“The night sweep was completed end of last week and we are working with our contractor to address all issues discovered,” Gallagher said Monday via email. The lights have a five-year warranty, Gallagher said.

Elk Grove made the call to convert to LED in early 2014, installing an initial 9,800 of the lamps. Elk Grove officials at the time cited energy, maintenance and cost savings. LED lamps are longer lasting and less light polluting than traditional sodium vapor lamps.

Elk Grove was among the wave of U.S. cities and jurisdictions in the last decade that hired American Electric Lighting and parent Atlanta-based Acuity Brands to retrofit its roadway LED lamps. The lighting giant behind many U.S. cities’ LED conversion projects reported nearly $1 billion in sales in its 2023 fiscal third quarter, the company announced in June.

The lamps’ eerie cast is nothing new. Cities across the U.S. and Canada have reported the purple and blue hues, including in Vancouver; Green Bay, Wisconsin, where the streetlights turned Minnesota Vikings purple; and Raleigh, North Carolina.

So, what’s causing the lights’ colors to change? A problem with the laminate that cloaks the fixture, officials at Duke Energy, the utility that supplies power to Raleigh and the region of North Carolina known as the Research Triangle, told Business Insider in 2022 and the Raleigh News & Observer this year.

With the protective coating, LED street lamps are bright white. When that coating degrades, the Duke officials said, the light takes on a purplish cast.

The same Business Insider article says heat damage was likely to blame, citing studies examining the effect of heat on LEDs.

That checks out in a Sacramento region punished by a string of 100-degrees days this summer and once again under a heat advisory issued this week by the National Weather Service.