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Why Street Lights Across America Are Turning Purple

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Streetlights tend to serve two main purposes. They exist to illuminate the streets for drivers to see better, and to make public spaces more welcoming and less scary for pedestrians at night. Traditionally, they’re some variant of orange or warm yellowish light, but in recent years, many have mysteriously turned purple. The change has confused motorists, excited Prince fans, and highlighted issues with municipal procurement.

The issue is currently a hot topic in Milwaukee, where significant stretches of highway are bathed in a lovely purplish glow. The city has pledged to rectify the issue in March, though the city’s purple patch has been in the news on and off for years now.

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It’s not just affecting the Cheese State, either. Reports of purple street lights have come in from Tennessee, North Carolina, Florida, Texas, Vancouver, and more. Even better, they’ve been spotted in Minnesota, in what must feel like a rather fitting tribute to Prince. Indeed, one YouTuber by the name God, Guns and Trucks took this loose connection as proof that the purple lights were a celebration of some kind of royalist New World Order taking over the United States.

Sadly, though, you’ll need to put your conspiracy theories aside. This isn’t some new cool hip trend in Departments of Transport across the country, and it’s not some attempt at widespread UV sterilization. Instead, it’s down to the switchover to LED streetlights that many municipalities have made in order to try and save energy. LEDs use a fraction of the power of most other lighting technologies, so they’re very attractive for government organizations trying to save money and cut carbon emissions.

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The unintended consequence was street lights in a powerfully purple hue. As it turns out, our resident RV lover Mercedes also loves these purple lights, so she’s taken pictures of the groovy scenes created by these lights in Lake Villa, Illinois, and St. Petersburg, Florida, and you can really see just how intense the coloring really is.

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A Nissan Sentra under the purple lights in St. Petersburg, Florida. – Mercedes Streeter

So why the purple? Well, in virtually every case, these bulbs were supposed to be white, or something close to it. Now, if you think back to your high school science lessons, you’ll remember that white light is actually made up of a whole bunch of different wavelengths. In contrast, a conventional single-chip LED only puts out a single wavelength of light. So, if you want white LEDs, you have to get tricky.

You could combine a red, blue, and green LED into a single package, and some white LEDs have done that, but it’s expensive. Instead, a lot of white LEDs are just blue, purplish, or UV LEDs at heart. Then, the outer casing of the LED is sprayed with a phosphor material. This phosphor captures some (but not all) of the blue light, and converts it to other wavelengths, typically yellow, but sometimes red and green as well. The combination of this converted light with the blue light passing through the phosphor provides a white or off-white output. By varying the composition of the phosphors on the bulb, it’s possible to fine-tune the exact shade of white light that comes out of the LED.

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This Department of Energy diagram shows how white LEDs work.

The reason these streetlights end up looking purple is because the phosphor coating has degraded over time. As it flakes off and there’s less phosphor to convert light, more of the core LED’s base color is visible. There are no other wavelengths being generated to sum up to a white or off-white color, so the bulb just projects blueish-purple light by itself.

It’s a strange defect, as noted by experts speaking to Scientific American. White LEDs are manufactured in the millions, if not billions every year, using the same phosphor-coating techniques. It seems that the lights chosen by many municipalities are failing due to bulbs with poorly manufactured phosphor coatings.

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A roundabout in Lake Villa, Illinois – Mercedes Streeter

Purple street lights have become popular photography spots for some automotive enthusiasts.

Most municipalities have elected to fix the problem by replacing the purple lights. As reported by the Milwaukee Journal Sentinel, the city first installed the defective lights in 2018, before realizing in mid-2021 that there was a problem with bulbs sourced from American Electric Lighting. An early estimate at the time suggested replacing all the affected lights would take 10 weeks or so across the winter period.

The problem didn’t go away, however. The Wisconsin Department of Transportation is preparing to replace more lights next month after they took a purple turn last summer. Even though the problem has been well-known and understood for years, it seems there are still bulbs out there failing. The Autopian has contacted the Wisconsin DOT to determine whether bulbs replaced in earlier work are now failing as well.

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A rest area in St. Petersburg, Florida – Mercedes Streeter

Meanwhile, in Texas, the defective lights, numbering 1,100 or so, were apparently sourced from Acuity Brands Lighting according to the city of Fort Worth. The same brand was reportedly responsible for a batch in Florida, too, while Maryland energy company BGE Now has replaced over 14,000 of defective Acuity-sourced bulbs under warranty in Baltimore alone.

The Autopian has contacted American Electric Lighting and Acuity Brand Lighting for comment on the matter, particularly regarding the factors at play behind the degradation of the bulbs. Notably, American Electric Lighting is a subsidiary of Acuity, as its website lives on the latter’s domain name. Acuity appears to be the prime brand behind the problem in most cases where a manufacturer is cited by public officials.

You might be wondering—is this really a problem? Isn’t purple a lovely color? I myself would agree, it’s quite fetching. And yet, it’s not really appropriate for street lighting. Like just about any other part of the road network, street lights are chosen carefully to offer the utmost in safety. They need to provide a clear, even light to help drivers spot hazards and other vehicles, without dazzling or otherwise distracting motorists. Studies have been undertaken that suggest cool white provides better visibility, with greater contrast and easier color perception, too.

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The Department of Energy has undertaken a great deal of research into solid state (LED) lighting, particularly for use in public at night. Contrast these two scenes—which has better visibility?

When they’re working, modern white LEDs are a big step up from the old monochrome orange sodium lamps.  It’s intuitive, too, that white light would be an improvement over monochromatic blue or purple light from these failing LED bulbs. Imagine trying to read a book at night solely under a blue lamp—you’d reach for a white light every time.

If you’re living somewhere with purple street lights, go out and enjoy them while you can. Your municipality is probably working to replace them, and if they’re not, they should be. As cool as they look, they’re really not the right choice when it comes to illuminating a roadway for safety reasons.

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Image credits: WFMY News 2 via YouTube Screenshot, Department of Energy

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Derek van Veen
Derek van Veen
1 month ago

KMART is having a blue-light special ™ on streetlights.

CTSVmkeLS6
CTSVmkeLS6
1 month ago

I’m in Milwaukee and can confirm. Until reading this I assumed it was intentional and thought to myself ‘this seems lass safe and also stressful on the eyes.’ Good to know!

Isis
Isis
1 month ago

The Subaru dealer near me looks like the whole place is lit up with blue LEDs. I thought it was intentional for some reason.

Nick Fortes
Nick Fortes
1 month ago

I just realized the article linked to the website for AEL and it has a whole section dedicated to Philadelphia. Like I mentioned earlier none of them appear to have failed near me, they’re all still super bright white. They got them in the overhead street lighting configuration here as well as the old timey street lamps type in Chestnut Hill which definitely look weird with a bright light shining off of them.

Madewithgenuineparts
Madewithgenuineparts
1 month ago

There’s a ton of these in suburban DC as well – good to know!

Nick Fortes
Nick Fortes
1 month ago

They updated all the street lights in a section of Philadelphia near me and they’re perfectly white but then there’s an Acme supermarket with the crazy purple glow coming from it. I was thinking they were just using the cheap version of the LEDs which is why they got the purple parking lot now.

Der Foo
Der Foo
1 month ago

My neighborhood replaces the older sodium lights with these newer LEDs starting just two years ago, if that. One particular light turned purple after only 3 months!! Others are still holding on with white or blue hues.

It was actually cool driving through a part of my neighborhood that I hadn’t been through in a while and seeing this one weird intersection bathed in purple. Extra points awarded because it was an unusual night with fog and I was out at like 2 AM. Kinda creepy, but definitely cool.

Calder Smith
Calder Smith
1 month ago

Honestly I love the purple lights. As the white ones die out here in Eau Claire, WI, they’re being slowly replaced with purple ones, and they bring a whole different vibe. They’re less harsh on the eyes, and I do truly find them easier to see in, especially considering I’m a delivery driver in a small hatchback. Every SUV’s lights are in my eyes, so to deal with that AND the blinding white streetlights is too much.

JumboG
JumboG
1 month ago
Reply to  Calder Smith

Blue and purple are the worst colors for night time lighting, red is the best. Exposure to blue or purple lighting will ruin you night vision temporarily.

Dave Beth
Dave Beth
1 month ago

They’re popping up here and there in Phoenix and the surrounding cities in Arizona too.

Bjorn A. Payne Diaz
Bjorn A. Payne Diaz
1 month ago

While LED’s may in theory and practice make things more visible, to me, that does not mean it makes people see better at night. They’re too fucking bright. It’s night time. Our bodies and eyes are in night mode. Lighting the streets like it’s a cricket match is a bit overkill even if the LED’s are an ultimate cost save to run and provide more/better light. You know what else saves money? Using fewer lights or lights that use even less power so as to not blind people.

My 0.02 Cents
My 0.02 Cents
1 month ago

It’s more that they are too white (color temperature), than bright (lumens). If they use a cooler color temp of say 2700 Kelvin (think older incandescent lights) instead of 4500 Kelvin or higher (much whiter light) they don’t hurt your eyes. and they don’t need to be so bright. Win win.
The lower cool temp of 2700 Kelvin has a longer wavelength so the light travels further for the same amount of brightness (lumens), so 2700 kelvin light doesn’t need to be so bright.
Another positive of cooler light is it creates less defined shadows as the light isn’t so bright.

Newer cars have the same annoying white lights too.

Bjorn A. Payne Diaz
Bjorn A. Payne Diaz
1 month ago
Reply to  My 0.02 Cents

You are correct. I didn’t want to jump straight into weeds of color temperature. 🙂

My 0.02 Cents
My 0.02 Cents
1 month ago

Yeah, I hear you there…
The trouble is people think oh I’ll get this whiter light to see better, then it has to be whiter and brighter to see as well. then we all get blinded.

Stick to 2400 – 2700 kelvin and increase / decrease the lumens as needed. then we can ALL see.

Side note. A huge thank you to the person(s) that invited auto dimming mirrors, these have saved my eyes on so many occasions, they now need to be standard equipment on every vehicle, including the outside door mirrors (Lexus has these I miss them).

TchmilFan
TchmilFan
1 month ago

Another advantage of other-coloured lights (purple/old sodium/whatever) is you could tell if there was other traffic was around – an advantage on urban junctions with poor sight lines.

DadBod
DadBod
1 month ago

I remember hearing that the sodium lamps were tuned in some parking lots to make acne really pronounced and skin tones generally unpleasant, which discouraged teenagers from hanging around. Probably the same teens who ate Pop Rocks, drank a Pepsi, and had their stomachs explode.

Last edited 1 month ago by DadBod
DEcarTrouble
DEcarTrouble
1 month ago

I have seen lights that are blue in color in Delaware and Maryland. The seem strategically placed though, near on and off ramps. Thought it was just a new thing. I actually kind of like the blue because it isn’t blindingly bright and allows me to see better in those situations.

Scottingham
Scottingham
1 month ago

I’ve known about this for a few years now once The Purpling started to hit in Chapel Hill.

When I tried to explain to the neighbors that it wasn’t supposed to be like that and then proceeded to explain the mechanism…they just nodded and backed away slowly.

Look who’s crazy now Cheryl!

My Goat Ate My Homework
My Goat Ate My Homework
1 month ago

So it sounds like someone was hawking cheap LEDs and now municipalities are paying for it. I’ll bet they were sold some shower rings too.

RataTejas
RataTejas
1 month ago

I know here in Fort Worth, they’re all being replaced under warranty at no cost to the city. In Calgary, Canada where I’m from originally, the city is footing the bill.

Never underestimate the value of your procurement and contract people for covering your ass.

My Goat Ate My Homework
My Goat Ate My Homework
1 month ago
Reply to  Lewin Day

You betcha, Del Griffith never sleeps.

TriangleRAD
TriangleRAD
1 month ago

Another great article about something lots of people have wondered about. When the purple lights started showing up about two years ago, word was it was a batch of defective Chinese LED’s. Seeing how widespread they have become, it seems to be way more than a single batch.

Before reading this article, I didn’t know about the phosphor coating being the culprit.

All that being said, I admit to being a bit fond of the purple lights. As the owner of a 1980’s car who is fond of the whole neon/synthwave aesthetic, I’ve been on the lookout for purple streetlights that are in good locations for taking pictures.

Steady progress has been made in my area with replacing them, so they are pretty scattered right now. I imagine if every street light was purple it would get old pretty quick.

Timbales
Timbales
1 month ago

Excuse me while kiss this guy

Cool Dave
Cool Dave
1 month ago

I hate the “feel” of LEDs. I understand how and why they are better and why there’s a push to put them everywhere but while they aren’t actually sterilizing anything, they feel sterile.

I think it’s funny the manufacturers putting that little fade on tail lights now to mimic what an old style bulb would do, subconsciously everyone prefers the warmth of a real bulb!

Aaron
Aaron
1 month ago
Reply to  Cool Dave

I think part of the problem is people tend to choose Daylight balanced LEDs or cool white because those seem like they’d be the more ‘natural’ option. I have soft white LED bulbs in my house and you’d hardly tell the difference between them and the few remaining incandescent.

Stones4
Stones4
1 month ago
Reply to  Aaron

Warmer temperatures in the living room, bedrooms, and hallways. Brightest, whitest I could find went in the kitchen and bathrooms. I’ve got reading lamps with both so I can pick and choose based on my mood.

Scone Muncher
Scone Muncher
1 month ago
Reply to  Cool Dave

One of the things about cheap LEDs is that (as the article mentions) they’re not really producing full-spectrum white light. Because the glow of current running through tungsten throws off full-spectrum light (plus invisible IR radiation) the colour reproduction is considered to be 100%; i.e. things look the colour they would under sunlight. LEDs have these peaks and valleys in their emission spectra so things look somehow ‘washed out’ even if it’s ‘bright’. The Colour Rendering Index (CRI) of a bulb measures how close it gets to the incandescent ideal.

It sure seems like marketing BS but I’ve noticed a visible (ha) difference between a CRI 95+ bulb from, say, Philips and a no-name CRI 80 LED. I’d steer clear of GE though, their bulbs make nice light but they don’t last.

Chronometric
Chronometric
1 month ago

The official lighting supplier of Prince, Hendrix, and Deep Purple.

Last edited 1 month ago by Chronometric
Greg
Greg
1 month ago

I would love to go back and see the OG supplier to this Acuity brand. I would bet a lot of money that if you trace it around, they pretend to be an American supplier to get the Government contracts but are actually drop shipping the low bin stuff from huge eastern warehouses.

I hope these towns and cities are being refunded, but we all know they aren’t.

Keep the grift alive no matter what, the true American way.

Stef Schrader
Stef Schrader
1 month ago

I hate these so much. I hate the blurple, and I hate the extra brightness. I know they use less power and make it easier to see, but the switch to hella bright lights outside my house feels wrong in the middle of a neighborhood. I want darkness when it’s sleepytime, goshdarnit. You shouldn’t be going at full speed down a residential road anyway.

Last edited 1 month ago by Stef Schrader
SonOfLP500
SonOfLP500
1 month ago
Reply to  Stef Schrader

Agreed. We live down a narrow country road that used to have janky, dim fluorescent lights that gave slightly more illumination than nothing at all, and felt about right. A few years ago, they were replaced by LEDs like little supernovas, that illuminate their immediate area in washed-out blue-white and plunge the areas in between into deep shadow because of the contrast.

Stef Schrader
Stef Schrader
1 month ago
Reply to  SonOfLP500

Yeah, the shadows are worse now, too!

Mantis Toboggan, MD
Mantis Toboggan, MD
1 month ago
Reply to  SonOfLP500

I find the idea of a country road with any lighting all confusing. Where I’m from streetlights of all kinds stop at the town limits. Do you live outside the US? Or perhaps in a heavily urbanized area where a lack of multistory buildings and defined street blocks is considered rural?

I’ve been interested in how people and the government define urban and rural. I’ve been classified as urban when I lived on a dirt road and am still classified as urban despite living on a 16 acre property surrounded by farmland three or four miles from the nearest town. Apparently because I’m within an hour’s driving distance of two mid-sized metro areas.

It makes me wonder because I see people talking about what percentage of the population lives in each setting and their figures seem off compared to my experience. And I’ve heard others with similar stories of being classified as urban while clearly living in a rural setting. I looked into it and the standard the government uses is a form of population density. The way they use it makes almost everything east of the Mississippi urban unless it’s mountains, swamps or otherwise completely unsuited to development. The standard unit is pretty much village sized.

SonOfLP500
SonOfLP500
1 month ago

You guessed about right. I live in Japan, on the edge of a town of about 200,000 people. The town limits are defined by designated agricultural land and forest, so the scene changes from suburban to rural as you pass the last house. This is typical in Japan: the surroundings can change from very urban/industrial to rural in a couple of blocks from a busy trunk road.
Our house is the second last house on our road, part of a small development on land that used to be a large farmhouse, otherwise it would be protected farmland. As it is, we pay a special low land tax because of the designation.
The road leading to it is only just wide enough for two small vehicles to pass each other in certain places, depending on both drivers having a half-decent sense of the width of their cars.
Most rural “B” roads are unlit, although you often find a single street lamp at junctions or side roads, like the lamp in the forest in Narnia.

MikeInTheWoods
MikeInTheWoods
1 month ago
Reply to  Stef Schrader

I wish there were some ordinances about lamp covers to shine the light only where needed. A lot of them blast light 270* downwards and sideways from 25′ up. It lights everything, including the night sky.

DC Nate
DC Nate
1 month ago
Reply to  MikeInTheWoods

If anything, LED lights should be able to provide more light without light pollution.

Tristan Hixon
Tristan Hixon
1 month ago
Reply to  DC Nate

Not at the color they are.

DC Nate
DC Nate
1 month ago
Reply to  Tristan Hixon

Fair point, the blue-purple light emitted does result in some significant scatter. I know I’ve read some studies on LED vs. Incandescent vs. Sodium vapor that showed improvements in light pollution switching to similar lumen output LEDs but can’t seem to find them. I know there are lots of variables when comparing these lighting sources and even more misinformation out there.

Tristan Hixon
Tristan Hixon
1 month ago
Reply to  DC Nate

Other than the greater directivity offered by LED, I can’t see how that’s possible – shorter wavelengths scatter far more and far sooner than longer, so LPS and HPS as a rule should produce significantly less sky-based light pollution due to their longer yellow-orange wavelengths. Most street lighting LEDs I’ve seen have been in the 4,000k-5,000k range, which has a significant short wavelength (blue) component.

Jason Smith
Jason Smith
1 month ago
Reply to  DC Nate

I think the studies you’re referring to were actually on Autopian (or the old site). I remember them specifically mentioning the shortcomings of retrofitting incancescent fixtures with LEDs (inceased scatter and light pollution) and how much better you can control the light scatter with LED fixtures.
I wasn’t able to find any old site or Autopian articles on this, but I did recall this video. Fair warning, Technology Connections is an amazing YouTube rabbit hole… https://youtu.be/wIC-iGDTU40?si=fO_b-Mw92MEmMWWd

Last edited 1 month ago by Jason Smith
Aaron
Aaron
1 month ago
Reply to  MikeInTheWoods

I’ve started to see some better directed lights out in the wild. Problem is the old school sodium vapor lights didn’t have shrouds and municipalities don’t want to modify anything more than they absolutely have to.

Scottingham
Scottingham
1 month ago
Reply to  Stef Schrader

You could always get a laser (or focused flashlight) and aim it at the sensor to trick it into thinking it’s daytime 🙂

Stef Schrader
Stef Schrader
1 month ago
Reply to  Scottingham

Tempting…tempting.

Trust Doesn't Rust
Trust Doesn't Rust
1 month ago
Reply to  Stef Schrader

Interesting. Chicago’s upgraded lights are designed to focus solely on the street and sidewalk, not people’s homes.
https://chicagosmartlighting-chicago.opendata.arcgis.com/pages/program-background-and-benefits#seven

I have a streetlight directly across the street from my house and I’ll admit it was pretty weird at first but there is less light shining into my bedroom.

Teokiya
Teokiya
1 month ago

I was assuming it was going to be like a sketchy pub toilet with purple lights to stop people finding veins when injecting heroin… 😛

Last edited 1 month ago by Teokiya
Dan Pritts
Dan Pritts
1 month ago
Reply to  Teokiya

That was my wife’s theory.

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