Why are there purple streetlights on Kansas City area highways? We found answers

If you’ve driven on Kansas City’s highways at night in the past few years, you’ve probably noticed a purple glow reminiscent of your favorite sci-fi movies.

A reader recently contacted The Star to ask why some of the streetlights along Bond Bridge and elsewhere around the metro emit this hue.

While some residents appreciate the purple lights’ nostalgic vibes, others have expressed concerns about their impact on visibility, light pollution and local ecosystems.

We reached out to the Missouri Department of Transportation and found that the purple glow is unintentional: Spokesperson Melissa Black told The Star that the color is caused by a manufacturing defect with the LED bulbs the department uses to illuminate roads across the state.

“We have been systematically going through and working with the manufacturer to get those replaced,” she said.

MODOT traffic engineer Ericka Ross estimated that the department replaced between 500 and 1,000 purple streetlights during its first round of bulb replacements in 2022. Now, the department is planning another push that will see hundreds more lights swapped out — although these replacements haven’t yet been scheduled.

Here’s what we know about the tinted lights around Kansas City.

Why are Kansas City’s LED streetlights turning purple?

The purple streetlight phenomenon isn’t unique to Missouri — it has been spotted around North America in places including Kansas, Utah, Texas, Florida and Canada. The explanation likely lies in a process called delamination.

Many LED light bulbs used for street lights actually give off a purple-blue light by default. In order to split this light into the whole spectrum of colors that creates white light, manufacturers paint a material called phosphor onto the diodes inside the bulb.

Experts believe that purple streetlights are a result of this phosphor coating peeling off or degrading away due to issues in the manufacturing process.

As a result, cities around the country have been replacing these defective bulbs — the vast majority of which come from the Atlanta-based manufacturing giant Acuity Brands. Kansas City is among them, with the issue seeing a resurgence in recent months.

“I thought we were kind of done, and then (the problem) popped back up again,” Black said.

Ross added that drivers can report purple streetlights directly to MODOT by calling its customer support number at 1-888-275-6636.

Do purple streetlights impact road visibility?

Black and Ross told The Star that, while they may look unusual, MODOT’s purple streetlights are safe for drivers.

“We do get complaints on and off about the purple lights,” Ross said. “We have actually measured the light intensity, and it does meet our minimum requirements.”

But while the lights may still be bright enough to see by, they aren’t as bright as their white counterparts — and experts say their color can have negative impacts on nighttime visibility.

“When the only light that’s available is blue, we don’t have as much ability to see fine details,” said John Bullough, a director at the Light and Health Research Center at Mount Sinai’s Icahn School of Medicine in New York City.

That’s because the human eye has very few receptors in the retina’s center that are attuned to the color blue.

While Bullough said he isn’t aware of documented increases in traffic accidents related to purple streetlights, he added that their hue makes it more difficult for the human eye to read signs and distinguish between different colors, potentially impacting road safety for drivers and pedestrians.

He recommended that drivers use their headlights — including the high beams, when it’s safe to do so — to improve visibility on the road.

“It’s always a good idea to use your high beams as much as you possibly can,” he said. “More light will definitely help counteract the effect from just the blue (light).”

What other impacts do purple streetlights have on their surroundings?

Bullough told The Star that while the blue family of visible light can have negative impacts on eye health and circadian rhythms over time at a high intensity, the light emanating from defective streetlights is nowhere near strong enough to affect humans’ health.

Of greater concern is the light’s impact on other living things, especially insects, migratory birds, aquatic life and nocturnal animals. DeAnn Gregory, a retired environmental specialist from the Missouri Department of Conservation, noted that even properly-functioning LED streetlights can disrupt local ecosystems.

“Since they are broad-spectrum lights, they have so much more blue light and that is the light that’s harmful to pollinators, to bats, to owls,” she said. “Amber-colored LEDs are now available, and those are strongly preferred over the bright white lights that are commonly used.”

Gregory also serves on the board of DarkSky Missouri, a nonprofit group focused on decreasing light pollution and artificial lights’ impacts on the environment. Her group sees the state’s upcoming streetlight replacements as an opportunity to install lighting that is less disruptive to local ecosystems.

“We are asking that the lighting engineers take into consideration environmentally sensitive areas,” she said. “Missouri needs to begin to transition to lighting that will not cause unintended harm to wildlife.”

Do you have more questions about infrastructure in and around Kansas City? Ask the Service Journalism team at kcq@kcstar.com.