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.
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.
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.
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.
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.
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.
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.
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.
Image credits: WFMY News 2 via YouTube Screenshot, Department of Energy
I actually have always wondered why there was a purple streetlight. There’s just one in my area, in an intersection I visit often in Caldwell Idaho.
That’s a pretty hefty warranty fix. My quick sums, in fairness using Aussie rates would put the 14,000 in Baltimore at about AU$15m, just in replacement cost Inc labour and traffic control, let alone admin.
The whiter white LED lamps may be safer, but they come at a cost: blue wavelengths of light produce significantly more light pollution than yellows or reds. My small city (205k people or so), since switching to LED streetlights, is now so bright at night that I can easily see my way around an unlit field surrounded by woods during a new moon without a flashlight. You can see planets and maybe a couple dozen stars, and that’s it. The horizon near downtown looks like the sun just went down an hour ago, at midnight.
Lol 200k people is a big ass city
205k doesn’t even get you within the top 100 cities by population in the US.
No, but it does get you within the top 2 cities by population in my state, so I reserve the right to call it a big ass city. It’s really really far from being small by any metric, that’s for sure. I like in a small(ish) city of 10,000.
I think only low-population states consider 10,000 people to even be a city. Around here, 10,000 people is a mid-sized town.
Yes, in this low population state, I consider my community which is incorporated as a city and has city in its name to be a city. I don’t think that’s different in higher population states………
Not really.
Yep. Hate hate hate. The extra brightness is messing with migratory birds, too.
And both human and animal circadian rhythms.
Interestingly, I actually have some thoughts on a design that would be less color accurate, but still have high visibility with significantly reduced light pollution and effects on circadian rhythm.
Thanks for saying this. As my neighbors continue to pile on floodlights so bright I can see in my backyard, and the sky glows orange in the direction of downtown, I’ve often wondered if I’m one of the last few people wanting, or even expecting, that it be dark at night.
A timely article for me. I was just driving through MKE last weekend and noticed all the purple and was wondering what was going on. Hadn’t had a chance to google it yet and now I know!
There are a few on my nightly drive this time of year. They are in the section of the freeway where they did a major reconfiguration of an interchange and they are definitely worse than they were last winter.
I miss the pale yellow glow of street lights that used to be the generic lighting of all the shmucks out in front of the bar smoking. Street lighting at night is an entire mood when you’re out getting into it.
Sodium-vapor lamps for life!
Huh! I have never noticed any purple hue from LED street lights in our Minnesota neighborhood. All I have noticed is they’re either bright af, or not working. *Shrug*
Here in the Land of Pleasant Living and the Baltimore Ravens, lots of us wish BGE wasn’t replacing all the purple reign lights.
If you have never looked into the details on how LEDs work, here is a great video from Veritasium. It talks about how green and red LED were relatively easy to create but it took more than 20 years later to produce a blue LED. Without it we would not have white LED or most of the electronics screens we know of today. All because one guy would not give up on it even when other people told him it could not be done and even his new CEO told him to stop wasting company money. Wonderful story and well told in the video.
https://youtu.be/AF8d72mA41M
That was such an amazing video!! To me it showed the promise, and horrors, of capitalism.
Tl;dw: the blue LED would not have been made if not for a capitalistic gamble and a bunch of other factors going right (like snooty researchers ignoring him and forcing him to build his own vapor deposition device, that later became an invaluable skill).
But then the owner of the company changed to a bean counting SOB who, despite profiting billions, never gave the inventor his fair share, or even close to it.
But that owner is a job creator! Hero of capitalism. He earned his billions.
What’s the problem?
They look cool and the UV sterilization thing is kind of funny even if not the reason 😛
UV is a spectrum just like visible light. These put out UV-A which is akin to deep red whereas you need UV-C (more like deep blue to violet) to sterilize things.
It’s even the same spectrum!
(I know you know, it was just worded funny)
A spectrum within a spectrum within a spectrum within a spectrum….
From my experience and from what I’ve read on the topic, they create a lot more eye strain as well as light scatter.
I was wondering what was up with that one blue street light! Thanks for this great informative article.
I hadn’t considered the photography possibilities, but aside from that I hate the things. Blue/purple is the WORST kind of light for your night vision and it looks cold and unnatural!
I have a similar beef with LED headlights, the jarringly white/bluish white and unnecessary brightness make it so much harder to see while driving at night than it used to be. I learned to drive before those were common and now I miss not being temporarily blinded every time there are modern cars in oncoming traffic. Even using the “look at the other side of the road” trick isn’t effective anymore, the ground still looks like a void every time LED headlights are shining at me.
Honestly, what was so bad about the government mandating that all cars used standardized headlight types? They were good headlights! There was nothing wrong with them! They worked well, looked good, and were cheap to replace since everything used them! Then car companies wanted to make their own headlights for aerodynamic reasons, which was fine at first, and then all hell broke loose.
LED headlights are a public menace and should be banned.
I thought this was just me wondering if the old eyes were failing me. I’m dazzled with every passing car anymore, and it’s not just bro trucks. I’ve had Toyotas, Hondas, and even Mazdas blind me, even in the truck.
It’s definitely not just you. I’m in my early 20s, not nearly old enough for my eyesight to be getting that bad, and it’s stressful to drive at night sometimes with how many LED headlights there can be. They really do mess with your night vision and make it harder to see.
I am not yet 40, and I basically don’t drive at night anymore. Between my astigmatism and these new lights I can’t see a damn thing. Throw in a little rain….
Headlight aiming also seems to have gone completely out the window, even on brand new vehicles. Seems they just install the headlight assembly at the factory, assume it will be close enough, and of course dealers pencilwhip the hell out of pre-delivery inspections, so they’re not going to check it either.
I’d love for headlight aim/glare check to be part of a routine safety inspection, but being states are increasingly deciding that safety inspections (at all) are a “waste of time”, not likely to happen anytime soon.
John Oliver had “Headlights” queued as a topic for the previous season of Last Week Tonight but, because of the writer’s strike, it didn’t get made. Unfortunately, they also have a policy of throwing out any subjects they don’t cover, so they won’t be carrying it over into this season.
A real shame because I’m sure it must be one of the most easily-fixed causes of many crashes, injuries and deaths.
That is a real shame. That would’ve been a great way to get the word out, and it’s not like that story isn’t a current issue or old news.
I remember the orange sodium vapor lamps from my youth.
There was one purple street light on the road behind me. All the lights in town were swapped around the same time, so this one is an oddity. I haven’t noticed it lately, but don’t know if they fixed it or I just got used to it. I’ll check tonight.
Saw five ‘purpling’ on my way home tonight. Not quite purple, but definitely heading there. I could actually see where part of the light was purple and part white on one of them, because I was thinking about this and staring up at streetlights on my way home like an idiot.
I like the yellow streetlights, myself. Feels as though they don’t burn out my retinas at night.
I hate these so so much. They actually hurt my eyes, and I think I have some kind of sensitivity to light in that part of the spectrum – I have a hard time reading the blue clock numbers on the stove, for example. Because of their intensity, these things are more than just a silly fun goof, they are actually painful and make it very hard to distinguish things bathed in the light.
The blue LED on your stove actually have wavelengths that hit the wrong part of your retina so they always kind of appear blurry. Truly the worse choice for anything requiring an interface. Glad that Blue LED cellphone craze of the early 2000s died.
Oh neat! I’ve always gotten bizarre looks when I try to explain that certain colors and intensities are impossible to focus on so I thought it was just a me thing. I guess most people just don’t notice?
They’re not purple, they’re Plum Crazy.
Congratulations, you managed to write an informative and entertaining post about purple lighting without resorting to any purple prose!
I once owned a purple car. I wonder if it would have looked white at night under these lights.
Based on my experience at an observatory, I bet it would look “metallic”, but otherwise devoid of color. I had some notes marked up with a red pen up there once, the red just dissapeared…
Cool.
I had a red Jeep Cherokee that looked grey under some older arc sodium (red-orange) lights. I imagine it would be a similar experience for you. It can be a bit disorienting when you’re looking for your car.
I just thought that they were blue lights and the idea was to prevent people from shooting up by making it hard to find a vein. There’s blue lighting under the freeway overpass next to the downtown train station where I live.
https://www.npr.org/2019/09/03/756976676/blue-lights-may-deter-intravenous-drug-use-in-public-spaces
They do that in some public bathrooms, yeah. However, compromising road safety to cut down on the handful of injecting drug users that use openly on the sides of highways isn’t a thing.
That’s true. The underpass with the blue lights has horrible visibility but it’s a surface street. Come visit beautiful Downtown Los Angeles and you will see people using IV drugs on the side of the street on the regular. Mostly on the overpasses and underpasses as opposed to the freeway.
Apparently the underpass I was thinking of was lit up in blue “as a tribute to first responders” but other places like Cambridge University in the UK experimented with blue lighting to deter people from sleeping and using IV drugs in public areas.
The blue lighting is often seen as a “solution” to prevent junkies from shooting up in a restroom stall. The blue light is intended to make it difficult to see their veins.
Of course, it doesn’t work in 100% of cases, and a destitute subset of junkies can be especially determined and stubborn to find a place to get their next high, so a lot of establishments such as public libraries, city/county/state/national parks, campgrounds, rest stops, bars, ect. then often converge on the same next “solution”: removing the stall doors or even removing the stalls altogether from their public restrooms.
That doesn’t tend to work either, as the junkies still shoot up. But I’m probably not alone in having had a number of awkward restroom visits which resulted as a consequence.
How’s this for an awkward bathroom visit? I work at a library in downtown LA and administered Narcan to a guy who overdosed in the bathroom stall. Pants down around his ankles, face down on the floor, glass d!ck in hand.
It’s a surprisingly common site, these days. Remove the stall doors, and the addict will still shoot up there, openly. I’ve seen it. The only thing removal of the stall doors accomplished is assuring that anyone who needs to take an unavoidable emergency dump, does so with anyone else in the room as an audience. And then there’s the issue of perverts.
Although I suppose that means the library(or other establishment) spends less on toilet paper and doesn’t have to clean the crappers as often. Probably a fringe side benefit that came as an unintended but all-too-predictable consequence.
NPR once had a story about a convenience store owner that installed greenish lights outside his store. The idea was young women would know the lights made their makeup look awful so they would refuse to hang out there and thus the hoodlums would leave too
It worked.
There were a couple that I had to pass under on the way to work a couple of years ago. That’s when I discovered that for some reason my brain thinks that this particular color is an indication that I’m about to pass out. It’s just a brief moment of not quite panic before the brain figures out I’m still quite conscious, but it was more than a bit disconcerting, and it happened every single morning until they were changed.
I still have no idea what caused the reaction – I even thought it was a pretty color – but it made the drive rather exhausting just knowing that the panic was waiting for me.
That’s… that’s really something. Never heard of anything quite like it!
Press release (if only) from Acuity Brand Lighting: We never meant to cause you any sorrow, We never meant to cause you any pain.
Thanks for this! I have a solitary purple one by me, and I wondered if it was a pilot test or something. I always notice it makes my wristwatch dial really pop.
Though it does make me realize how much we took it for granted that yellowish light at night was just “normal.”
Yellow sodium lights come with a very substantial advantage in mixed lighting conditions in that they do not cause nearly as substantial effect on night vision. So, when entering and exiting lit interchanges on a highway that is unlit for instance, you wouldn’t lose as much night vision from the lit area.
The same problem exists with Xenon/LED headlights, aside from source strength the blue/purple kills your night vision. It’s not the glasses of nostalgia, it DID used to be easier to see while driving at night.
That’s a fascinating point – thank you! It does explain why the lit-up to dark transition can seem really jarring to me these days. Sure, I’m getting older, but I figured that wasn’t totally it.
I always hated LED headlights, and now you’ve explained to me why I hate them! Thank you.
Now if only we could return to those lovely old cheap sealed-beam headlights that never got faded, looked nice, resembled eyes, were plenty bright with a lovely yellowish hue, and only cost like $18 to replace. Those were peak headlight design and everything else has been a mistake.
Exactly this. Personally, I think the sodium lamps were better as a tradeoff between night vision (better with the yellow light) and color contrast (better with LED)
I don’t frequent the south side of MKE, looks like I need to go exploring and see what’s going on.
I do wonder what the astronomers think about all this. I always heard one of the reasons for the old yellow sodium-vapor lights was that astronomers could easily filter out the monochrome glare and it didn’t interfere with observations like other light pollution. But that doesn’t seem like as much of a concern anymore, if that was ever a real thing in the first place.
That was low pressure sodium bulbs. They had a very narrow-spectrum emission in the yellow band of the visible spectrum, but they haven’t even been made in several years. The high pressure sodium bulbs that are also used in street lights have a much more broad light spectrum.
Of course, from a pure research perspective it’s not quite as vital anymore. Unlike in the 1920s when sodium bulbs came out, we have radio telescopes and have put optical telescopes in outer space now. 😉