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I wrote an article about this almost a year and a half ago, and I was wondering how it's held up. I think Scientific American is remiss in not digging a bit deeper, because to me one of the main parts of this story is a commercial phenomenon - street lighting in the US is pretty monopolized, almost all municipal street lights and a good portion of area lights are made by the same company (Acuity). That makes it a lot less surprising that they would exhibit a similar failure around the same time.

Acuity has acknowledged a phosphor defect in their lights and had launched a major warranty repair campaign, but I'm not sure how well that's gone given that new failures are still occurring. At least a year ago, they were struggling with the scale of the problem: it just takes a long time to schedule replacement of failed fixtures when there are so many of them.

It’s a fairly common failure it seems. Here’s it happening in Ireland:

https://www.irishtimes.com/ireland/dublin/2025/02/05/almost-...

I had someone complain to me about how it was a change made by the Green Party for bats: how ridiculous!

No, it’s just a faulty light…

A friend and I found a contractor to give us a couple of these lights in the Phoenix area. We traced the LEDs back to a Seoul Semiconductor Phosphor on-chip design. We still have a suspicion that LM80 testing didn’t catch this and it was due to a thermal cycling failure. https://m.youtube.com/watch?v=4Mll-YDDAF4

As someone who walks a lot (including, for many years, back late at night from work or school), I really wish they'd made the LED streetlights approximate the original warm color temperature from the start.

Instead of going bright white, high-color-rendition, wake-up-and-kiss-your-sleep-schedule-goodbye, which is what they went with instead.

When the LED streetlights were first installed, they were horrible, and we were promised they would be adjusted, but they never were sufficiently.

Maybe caring about the look of neighborhoods, and the sleep of people who walk or have unfortunate bedroom window positions, would've had a side effect of avoiding the problem in the article?

> people driving at night may notice a moving object in their peripheral vision more quickly under bluish-white light than under yellowish-white light, [...] Gaining improved peripheral vision under blue-tinged light comes with a trade-off, however: once the moving object comes into focus, it becomes harder to see.

If we were switching away from LED to sodium vapor lamps instead of the other way around, they would have written the exact same article but in reverse, still claiming the change makes us less safe.

Here's a video on the topic from 2 weeks ago: https://www.youtube.com/watch?v=Jfr8fmF8oJU

Pretty interesting.

I've never seen a LED streetlight turn people where I live. Sounds like bad light design and the LED is perhaps getting too hot.

Though that said, just go and replace them as they would have had to for sodium vapour lamps they had before? And this time replace them with something that runs them at a lower temperature, especially if the environment during a summer could be hot from external temperature.

It’s interesting how many people assume these purple lights are some kind of new design choice. But really, it’s just a side effect of the phosphor layer breaking down in the LEDs.

Makes you appreciate how tricky it is to balance cost, lifespan, and quality when you’re manufacturing millions of these for cities.

Read somewhere a few years ago this was a manufacturer defect and they were in the hook for replacing them all.

I've (not seriously) considered buying a pellet gun to shoot out the 4 massive neon purple lights at the entrance to my quaint 1970s era neighborhood. They didn't remove the old light poles after installing the new ones about 3 years ago, so it's double lit with sodium vapor and purple now.

Curious is there is a single person on the planet that prefers the white (er, purple) street lights?

> And yet some streetlights have suddenly turned a jarring shade of purple. It is hard to determine the exact cause without dissecting one of the defective lights, but scientists have a hypothesis: bright purple light suggests the phosphor layer around the lights has been “delaminated”—peeled off—exposing the blue LED light underneath, Brgoch says.

What an annoying/bad article. "Here are our guesses of this when we could have actually figured it out". It's not like these are in space and hard to get to, they are on the freaking street. Get a crew out there and figure it out.

Then they go on to do a _bunch_ of handwavy "science" about blue light while not really making any point (IMHO).

> One thing that Bullough suggests pedestrians and drivers do to stay safe under purple streetlights—or any lights, for that matter—is to remove sunglasses and blue-light-filtering glasses when walking or driving at night.

Ahh yes, for all the people that wear their sunglasses at night, I'll make sure to let Corey Hart know.

This just seems like an incredibly low-effort article with zero definite facts and enough hand waving to sprain your wrist.

It is not directly related to the article, but the decaying LEDs mentionned in the article made me think of it.

Since we had to switch to LEDs, I had to change lightbulbs waaay more often. I realize they consume less (even if here they would just help heat the house so the energy is not lost), but hell they are crap. They start blinking, their color is shifting, they die quickly, they are super expensive, they are bigger and many lamp I had couldn't be fitted with LEDs unless I found some smaller ones which are even more expensive.

This is my personal anecdotal experience, but I would be interested if any serious study had looked into this kind of issues.

My LCD TV did the same thing with a few of the backlight LEDs. Makes a big purplish splotch on the screen. Replaced the backlight strips and took the lens off of one of them and was surprised how small the LED is -- tiny yellow 1.5mm squares.

There's multiple adjacent parking lots in my city that are full of street lights that emit blue light. I've been wondering for awhile why in the world they would be blue but I think I got my answer. Probably someone trying to cut costs a bit too aggressively. My city and state are known for skimping on anything and everything when it comes to streets and roads.

“ producing light that is comparable or better in quality.”

They don’t support this claim about led’s, and many groups are concerned about harsh cool light interrupting circadian rhythms. They’re also hideous.

To be honest, I quite like this atmosphere. Some roads near my home now feel like something out of a science fiction movie when walked on at night. Of course, traffic safety may not be good, but walking at night adds a sense of fantasy.

Even the streetlights protest the anti-LGBT narrative in the US :)

"LED Filaments" are a more direct example of phosphor-coated blue.

Most everyone has seen these now, in "Edison Bulbs" or elsewhere.

https://en.wikipedia.org/wiki/LED_filament

Better article with lots of pictures and diagrams, links to conference talks, etc:

https://inside.lighting/news/24-05/heres-why-led-streetlight...

one of the biggest roads in my town has these purple lights at night, and it's very off-putting honestly. Makes it kind of hard to see things properly. I specifically avoid this road at night now because of it.

A Trader Joe's in Phoenix has had these for so long (years?), the parking lot is bathed in almost completely blue light. They don't seem to care. It really throws off your vision and things look "fuzzy".

This is happening everywhere where I live (Vancouver)

This is wrong about phosphors in the initial explanation, no? They are actually quite broadband AFAIK.

Trade-off-aware software engineers discussing streetlight variant choices is the infinite loop of endless discussion.

Wow!

The comments here!

Are we really such neo-phobe curmudgeons? Sodium hallide street lights preferred over LEDs?

Golly Hacker News, get a grip and join the modern world!

Glad I converted nearly all of the lights in my house to halogen, and stocked up on decades of bulbs, before the ban. Nice warm adjustable light. No strobing LED trash fucking up my eyesight.

I have to say I'm disappointed in the level of discussion on this subject (elsewhere online and here on HN.) It is obvious to anyone who has ever paid attention to an LED that this is a failure of the phosphor adhesion; more specifically, the phosphor (a fine powder which converts the nearly monochromatic blue-purple LED light to the broader white) is held in silicone, in a small dab on the surface of the LED. The fact that this silicone lasted only a few years is the surprising part; sure, the environment inside the streetlights is harsh (large temperature and humidity swings) but a high-quality silicone should be able to handle this for significantly longer.

It would be nice to read some discussion of the core issue - the silicone - to me, it seems like a total failure of the silicone and not just an adhesion issue, as the photos seem to demonstrate small cracks leading to larger cracks and then total failure. Perhaps related to the addition of something new to the phosphor mix, which might change its properties under thermal cycling? Poorly mixed silicone? Unsteady temps as the silicone was applied?

An apartment building a few blocks over from me has these. It makes the whole area look like a night club. Very weird.

TL;DR - coating is wearing off.

We had some of these on my street. Honestly liked them better than the full power ones they got replaced with.

Tldr “ bright purple light suggests the phosphor layer around the lights has been “delaminated”—peeled off—exposing the blue LED light underneath, Brgoch says. Although blue LED lights are, in principle, deep blue in color”

I find it somewhat amusing that they had to find "scientists" to explain this, when the purple tinge is something that LED TV repairmen have been dealing with for around a decade now. However, they're correct that it's because the phosphor layer is getting damaged, probably because they're being driven too hard by the LEDs, which are now being optimised for brightness and recurring revenue instead of longevity and efficiency.

Also, I personally think spirited driving on a purple-lit nearly empty highway at night is a uniquely fun experience with an 80s-retro-futuristic vibe. The streetlights are merely accent lighting at that point; the highbeams are for actual visibility.