Street Lights turning Purple

[TimFox]

Recently in Chicago, I have noticed a problem with another common light, which I believe now uses LEDs.
There is a standard square electrical sign for "no left turn", which has a red circle and diagonal bar over a white right angle icon for "left turn".
I now see many of these where the red circle and diagonal is clearly visible, but the white "left turn" icon is barely visible.

[AlbertL]

I saw my first purple streetlight recently, in my neighborhood in Fairfax County, VA (about 8 mi. west of Washington, DC).

Some people are making good use of them: https://www.tampabay.com/photos/2021/07/05/tampa-photographer-uses-damaged-streetlights-to-create-art/
and want to keep them: https://www.change.org/p/manitoba-hydro-keep-the-purple-led-street-lights-in-winnipeg .

[AlbertL]

My friend who works in the streetlighting industry was just talking about this the other day when I was hanging out with him. He said it is a particular brand and model of luminaire that is having this problem, he's been working on getting me a defective one to do a failure analysis on.

Here's a report citing a conversation with a manufacturer's representative who confirmed that the problem is failure of the phosphor coating: https://schaumburg.novusagenda.com/AgendaPublic/CoverSheet.aspx?ItemID=16260&MeetingID=2566 

And another mention: https://streets.mn/2022/03/21/spring-2022-highway-news-roundup/ (second item on page)

[Ground_Loop]

I just drove into Atlanta airport and saw literally dozens of the street lights that had gone purple. Sorry no pics, but it looked to be around 25% had the problem.

With pics

[james_s]

That's going to be disastrous for the manufacture. They do look pretty cool though.

[SiliconWizard]

Ahahah!

[PlainName]

If these lights are because of the phospor failing, isn't the UV being blasted out? Wouldn't there be a health hazard at least to your eyes?

[Zero999]

Will the traffic lights be turning blue tomorrow?

No, they use dedicated colour LEDs.

Not for red and unlikely for bluish-green, but phosphor converted LEDs are sometimes used for amber, because LEDs in that region of the spectrum are notoriously inefficient. I wouldn't know for sure whether these are used in traffic lights, but it wouldn't surprise me.
https://www.lighting.philips.com/main/support/support/faqs/white-light-and-colour/how-is-amber-produced
https://phys.org/news/2009-07-yellow-gap-full-conversion-blue.html

[WatchfulEye]

If these lights are because of the phospor failing, isn't the UV being blasted out? Wouldn't there be a health hazard at least to your eyes?

There should be zero UV emission as the pump LEDs are blue and, as is typical for LEDs, have a very narrow emission spectrum which would not extend to UV.

While UV LEDs exist, they are substantially more expensive. They seem a poor choice for illumination, as you would need to phosphor convert the blue light as well as red/green, reducing efficiency and complicating phosphor design.

Blue light alone is unlikely to have major health effects at the intensities seen here. There is some concern over disruption to circadian rhythms, and there is a current fad about blue light reduction some of which is questionable at best.

At high intensities, any visible light can cause eye injury due to direct phototoxicity (prolonged saturation of photoreceptors results in biochemical imbalance which is toxic and can lead to cell injury). This can occur if you stare directly at a high intensity LED especially if it has collimating optics (eclipse viewing with an inadequate filter is a well recognised cause, as is deliberate misuse of laser pointers), but this is unlikely to occur by accident.

[SiliconWizard]

Agreed. There's very little UV emitted by LEDs made for lighting.

Beyond the spectrum, the amount of external ligthing at night is a real environmental problem. And a potential health issue at least for animals that cannot escape it.
It's not very hard to figure that billions of years of evolution with basically no light at night (just moonlight) have shaped organisms in a way that a sudden change with constant night lighting above the brightness of moonlight will cause problems. But we don't care, as we must do what we want. Ha!

[AVGresponding]

Oh come on, it's not like night flying insects and animals do anything useful like pollinate food crops... oh wait...

[Zero999]

Agreed. There's very little UV emitted by LEDs made for lighting.

Beyond the spectrum, the amount of external ligthing at night is a real environmental problem. And a potential health issue at least for animals that cannot escape it.
It's not very hard to figure that billions of years of evolution with basically no light at night (just moonlight) have shaped organisms in a way that a sudden change with constant night lighting above the brightness of moonlight will cause problems. But we don't care, as we must do what we want. Ha!

Yes, low pressure sodium was less of a problem for people and wildlife alike. I believe there are some areas where they've switched to longer wavelength LEDs, where the blue/white ones have been shown to be problematic to wildlife i.e. nesting turtles.

[PlainName]

Oh come on, it's not like night flying insects and animals do anything useful like pollinate food crops... oh wait...

Don't flowers close at night?

[Zero999]

Oh come on, it's not like night flying insects and animals do anything useful like pollinate food crops... oh wait...

Don't flowers close at night?

Some flowers do. It depends.

[AlbertL]

That's going to be disastrous for the manufacture. They do look pretty cool though.

Yes, especially because in some jurisdictions the manufacturer is also on the hook for the cost of the labor to replace the fixture.

[james_s]

My friend who works in the streetlighting industry was just talking about this the other day when I was hanging out with him. He said it is a particular brand and model of luminaire that is having this problem, he's been working on getting me a defective one to do a failure analysis on.

Here's a report citing a conversation with a manufacturer's representative who confirmed that the problem is failure of the phosphor coating: https://schaumburg.novusagenda.com/AgendaPublic/CoverSheet.aspx?ItemID=16260&MeetingID=2566 

And another mention: https://streets.mn/2022/03/21/spring-2022-highway-news-roundup/ (second item on page)

Just saw this. Whoever wrote the document keeps using the word "phosphorus" instead of the correct and completely different term "phosphor". 

[Zero999]

My friend who works in the streetlighting industry was just talking about this the other day when I was hanging out with him. He said it is a particular brand and model of luminaire that is having this problem, he's been working on getting me a defective one to do a failure analysis on.

Here's a report citing a conversation with a manufacturer's representative who confirmed that the problem is failure of the phosphor coating: https://schaumburg.novusagenda.com/AgendaPublic/CoverSheet.aspx?ItemID=16260&MeetingID=2566 

And another mention: https://streets.mn/2022/03/21/spring-2022-highway-news-roundup/ (second item on page)

Just saw this. Whoever wrote the document keeps using the word "phosphorus" instead of the correct and completely different term "phosphor". 

I also noticed that, but couldn't be bothered to mention it here. It's quite common for people who are unfamiliar with LEDs and lighting.

[james_s]

I also noticed that, but couldn't be bothered to mention it here. It's quite common for people who are unfamiliar with LEDs and lighting.

It drives me nuts, I remember noticing it in a show about how fluorescent tubes are made too. It's such a rookie mistake that immediately tells me the person writing doesn't know what they're talking about. It's like silicone and silicon, similar sound, big difference.

[Sal Ammoniac]

The debacle of Detroit's streetlight failures- over 20,000 "prematurely dimming and burning out" cost almost $7M to replace them. They failed melting the lens.
Detroit Sues Lighting Manufacturer Over Failed Street Lights The City sued Leotek Electronics, got only $4M in settlement.

Point is it's very expensive labour-wise to swap out defective streetlights, about 1,500 a week were done and the City of Detroit contracted out all streetlight work, they didn't have their own crews.

Fun historical fact: Before the turn of the 20th century Detroit had 122 175-foot tall Moonlight Towers to light up 22 square miles of the city center. Austin TX still has some of these towers.

[PlainName]

Wow! It works really well in that photo! Almost as good as daylight.

[fourfathom]

Will the traffic lights be turning blue tomorrow?

No, they use dedicated colour LEDs.

Not for red and unlikely for bluish-green, but phosphor converted LEDs are sometimes used for amber, because LEDs in that region of the spectrum are notoriously inefficient. I wouldn't know for sure whether these are used in traffic lights, but it wouldn't surprise me.
https://www.lighting.philips.com/main/support/support/faqs/white-light-and-colour/how-is-amber-produced
https://phys.org/news/2009-07-yellow-gap-full-conversion-blue.html

C'mon guys!  That's a Jimi Hendrix quote:

The traffic lights, they turn blue tomorrow
And shine their emptiness down on my bed
The tiny island sags downstream
'Cause the life that lived is dead
And the wind screams, Mary

From The Wind Cries Mary

[Ben321]

The phosphors are inside of the LED component itself. There's the blue gallium nitride blue emitter chip itself, which is then coated with a layer of yellow fluorescent material. This entire structure then is fully encapsulated inside the dome shaped piece of clear plastic. And by encapsulated I mean that liquid plastic is poured over the chip+phosphor structure that's sitting in a dome shaped mold so that the chip+phosphor structure is completely potted. There's absolutely no way for it to flake off. Overheating could burn out LED or even explode it, but the phosphor can't flake off while the LED is operational because it's physically sealed by the surrounding plastic. And of course if it burns out or blows up, the LED stops emitting all light.

Have you ever seen an SMD LED? I have never seen any lighting solution with outdated through-hole LEDs.

Don't those SMD LEDs have a clear plastic layer over it though, so that it protects the inside of the LED? Also I've seen some cheap dollar-store LED flashlights with like 10 low power through-hole LEDs, rather than a single high power SMD LED.

[Ben321]

Almost all commercial white LEDs are blue LEDs with phosphors ontop.  These street lights sound like they're losing their phosphor layers.

Temperature x hours too much for them?  Or maybe something more creative like the phosphors flaking off due to moisture and cycling?

The phosphors are inside of the LED component itself. There's the blue gallium nitride blue emitter chip itself, which is then coated with a layer of yellow fluorescent material. This entire structure then is fully encapsulated inside the dome shaped piece of clear plastic. And by encapsulated I mean that liquid plastic is poured over the chip+phosphor structure that's sitting in a dome shaped mold so that the chip+phosphor structure is completely potted. There's absolutely no way for it to flake off. Overheating could burn out LED or even explode it, but the phosphor can't flake off while the LED is operational because it's physically sealed by the surrounding plastic. And of course if it burns out or blows up, the LED stops emitting all light.


I have a hypothesis about the ones turning purple or blue. I think that there's those are using tri-color non-phosphor LEDs. These are the same type that are used in RGB LED advertising signs that can display bright full color pictures on billboards. Except here they are being used not for image display, but rather for illumination. My guess is that the drivers for green LED chips and red LED chips are failing faster than the ones powering the blue LEDs, resulting in the blue color you see from them when they fail. While most LED streetlights use the normal white phosphor design, I think a few are using tri-color LEDs and these are the ones that turn blue when they fail.

Why would the green and red LEDs fail first? If they were RGB then a good number of them would turn yellow, or cyan, rather than purple.

It's phosphor failure. The reason why some change purple is because violet, rather than blue LEDs are often used to excite the phosphor.

Cobra head LED light fixtures fail for many reasons - overheating, water ingress, cheap/overstressed components like the LED's, electrolytic capacitors etc. and thermal cycling, bad driver design, lightning/transients, loose bolts falling down and many more reasons.

For the purple/blue streetlights, "American Electric Lighting (AEL) a division of Acuity Brands Lighting products" seems to be just a middleman, a dealer of numerous lighting brands.
Their warranty is the usual 1 year, liability limited to the purchase price of the product. A few warranties went to 6 years on select components.
Our municipality's tax dollars pay for these failures but it's always hush hush and swept under the rug because it's very expensive to replace streetlights, labour-wise.

For Detroit, LEOTEK is part of Lite-On Group.
So is their melting LED "cheap" or driven at the datasheet maximum? You want the highest lumens number in order to make the sale, who cares about lifetime- by then you will have bought your Lambo and can blame someone else.

Laws vary. In some countries the manufacturer still has a statuary obligation to the customer, beyond a year, or whatever the warranty states. If a large number are failing too soon, they still might be able to get some money from the manufacturer to replace the failed luminaries.

Regarding the LEDs turning color, it could be cheaply made LED driers. Typically for the 20mA through hole LEDs, red LEDs have a voltage drop of about 2 volts, while green LEDs have a slightly higher voltage drop (close to 3 volts), and blue have even higher (about 4 to 5 volts).  So if the LED drivers were using a simple resistor, and all of the drivers of different colors were using the same resistor value. The lower voltage drop of the red LEDs would cause them to draw more current through the resistor, causing them to fail first. Obviously these aren't low power 20mA LEDs being used, but the idea scales up to the higher power LEDs anyway, because the higher power red green and blue LEDs still use the same semiconductor materials (so now the voltages across the devices are higher, but by the same ratios). I could easily see a cheap Chinese company doing something like using simple resistors (not constant current LED drivers) and even using the same value of resistor for all 3 colors, just to cut costs, even if it shortens the usable life of the product. So I'm guessing that the LED streetlights you see failing were all made by some Chinese company who made them on the cheap, with shoddy design (specifically shoddy in the way I described above).

[Ben321]

I just drove into Atlanta airport and saw literally dozens of the street lights that had gone purple. Sorry no pics, but it looked to be around 25% had the problem.

With pics

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Some look blue and others look purple. Is that just the result of how the camera captured the light, and they all actually had the same color (either blue or purple)? Or is that actually what they looked like (some being blue and others purple)? And I can't imagine all of them failing together such that an entire stretch of roadway had these defective LEDs. I also have never personally seen LED streetlights fail this way. The ones I've seen fail blink at a fixed rate like a strobe light (at about 2 to 4 flashes per second), but their color stays the same as when they were fully operational.

[PlainName]

all of them failing together such that an entire stretch of roadway had these defective LEDs

They will buy and build in  bulk, so if it's a batch problem it would likely affect adjacent lamps.