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[Scott5114]

Just got back from a short daytrip in NE Kansas. There were a few towns where some or all of the streetlights used blue LEDs instead of white. (Note that this isn't just meant-to-be-white lights with a blue tinge, they were blue blue.) Most of the lights in Winchester were like this, and a few here and there in Leavenworth.

What is the reasoning for this? Or was it just a weird Christmas thing?

[Bobby5280]

Blue street lights? I guess I would need to see how effective the street lights are at illuminating the surroundings before passing judgment.

Just going by my experience of using blue LEDs as a light source inside channel letter building signs it seems like a bad idea to use blue LEDs in street lights. If it's my choice to make in a sign design I never ever specify blue for channel letter faces and illumination. That's because that darker blue color is far less legible than warmer colors with much shorter light wavelengths. Even if the blue color is really brilliant the sign often ends up looking "fuzzy." It can literally be hard to focus on a lighted blue channel letter sign. The effect can really be pronounced for anyone who is near-sighted. Red, yellow, orange and even green all stand out better.

Every now and then we have to make blue channel letter signs because that's just what the client wants. Blue is pretty. So they want it. We try warning them about it and even give them examples at specific business locations they should check out at night time. Some customers can be put off by the warnings. But it is an extremely worse PITA if you just say nothing, make their stupid blue channel letters and let them discover the damned things aren't very legible at night time. "There's something wrong with my sign! How come you didn't tell me blue wasn't as legible as red, white, yellow or whatever!?" They try to make the failure of their artistic request your fault. We warn them up front about the bad idea to cover our asses.

I've seen a growing number of white LED-based street lights in some upper income suburbs. I prefer their lighting effect over the amber color of high pressure sodium street lights that have been popular for around the past 30 to 40 years. When I was a little kid it seemed like there was a lot more white street lights with a blue-green tinge; I think those were mercury vapor-based lamps.

I'm pretty sure the white LED based street lights consume less power and have a lower overall cost for the life of the lamp. We're not yet seeing a widespread move to replace high pressure sodium lamps because the LED-based street lights have a higher up front cost.

[Scott5114]

It kind of depends on where you are. Back in Oklahoma, most of the City of Norman's street lights are LED now, at least on the main streets. But the ODOT-maintained highways still have the orange sodium vapor lights. 

The blue lights I saw up here in Kansas were bright enough that you could see them, but they were noticeably darker than the white ones. I wonder if it's an attempt at preserving drivers' night vision or something like that.

[Scott5114]

Update: did a bit of Googling and it appears that these are due to premature component failure from a batch of defective light fixtures. Many Kansas cities have reported them. It seems like the bigger cities have gotten all of their defective lights fixed. Perhaps Winchester simply thinks their lights are supposed to be like that.

[Dirt Roads]

Surprisingly, LED street lights are in the very low frequency range and not wide spectrum (as would be indicated by the color white).  There have been numerous reports of LED street lights experiencing a failure mode that makes them look purple, or in a worst case, they look blue. 

A true white-emitting diode does indeed exist, but they are still very expensive.  Instead, less expensive white LED arrays are a combination of different color LEDs arranged such that the light wavelengths appear to cover much of the spectrum (hence the appearance of the color we call white).  When the green LEDs in the array get weak, the color appears as purple and when both the red and green LEDs get weak, you get a full-on blue hue.  But there is also a technology that shines blue LEDs through a phosphor substrate to achieve a white color.  If the phosphor surface is damaged, it would also show up as blue (I don't believe that these have a failure mode to create purple, so it is unlikely that this phosphor technology is the one being used).

Last year, there was a problem in Wichita where most of the new streetlights from a particular manufacturer turned blue and were scheduled for replacement.  I haven't been successful finding out the manufacturer, but I highly suspect that these issues have become more frequent after a particular LED manufacturer walked away from that market.  Stay tuned.

Full disclosure:  I was closely involved with the original development of the white LED while working as a consultant for New York MTA overseeing that particular project at New York City Transit (NYCT Subways).  I really didn't get involved in the technology, as my role was entirely on the financial and scheduling sides.

[edwaleni]

Surprisingly, LED street lights are in the very low frequency range and not wide spectrum (as would be indicated by the color white).  There have been numerous reports of LED street lights experiencing a failure mode that makes them look purple, or in a worst case, they look blue. 

A true white-emitting diode does indeed exist, but they are still very expensive.  Instead, less expensive white LED arrays are a combination of different color LEDs arranged such that the light wavelengths appear to cover much of the spectrum (hence the appearance of the color we call white).  When the green LEDs in the array get weak, the color appears as purple and when both the red and green LEDs get weak, you get a full-on blue hue.  But there is also a technology that shines blue LEDs through a phosphor substrate to achieve a white color.  If the phosphor surface is damaged, it would also show up as blue (I don't believe that these have a failure mode to create purple, so it is unlikely that this phosphor technology is the one being used).

Last year, there was a problem in Wichita where most of the new streetlights from a particular manufacturer turned blue and were scheduled for replacement.  I haven't been successful finding out the manufacturer, but I highly suspect that these issues have become more frequent after a particular LED manufacturer walked away from that market.  Stay tuned.

Full disclosure:  I was closely involved with the original development of the white LED while working as a consultant for New York MTA overseeing that particular project at New York City Transit (NYCT Subways).  I really didn't get involved in the technology, as my role was entirely on the financial and scheduling sides.

Unfortunately where I live the LED fixtures fail by strobing. It makes you feel like you are in a night club.

[Bobby5280]

LED technology has made great strides over the past 10 or so years.

The first generation of "white" LEDs were really blue LEDs that were over-driven (and thus had a shorter life span). Today true white LEDs are increasingly common. My company uses them all the time for internal lighting in sign cabinets, channel letters and other more unique applications (border lighting, environmental lighting, etc).

For service calls we've retro-fitted lots of older, existing sign cabinets that were formerly lighted using T12 HO/D fluorescent lamps with new LED-based lamps. There are LED sticks made in the same form factor as the old lamps. We do replace the old higher voltage ballasts with new low voltage power supplies. Prices for the LED lamps have come down a good bit since production of the lamps have hit larger scales. The customer ends up saving quite a bit of money on the sign's electric bill.

New variable message displays, such as the full color "jumbotron" screens you see in sports stadiums, are so much better now than in the past. Early generations of those boards ran at 60Hz and the LEDs weren't nearly as brilliant. I couldn't take a digital photo of one of those things without locking the camera down on a tripod and shooting a slower exposure, such 1/30. Sometimes I ended up having to take two different exposures, one for the LED display and another for everything else and merge them together in Photoshop. I don't have to do that crap anymore.

A modern board from Daktronics or Watchfire will have a refresh rate running thousands of hertz. If you point a video camera at it you're not going to see any flicker. Still photos aren't going to show missing parts of an image. The color depth of these boards is very wide; there is no problem showing high dynamic range imagery on these things even though most content shown is just standard 24-bit RGB. The overkill is built in to allow fine tune adjustments over the years as new tiles are added to replace old damaged ones. You can adjust the overall balance to avoid a square quilt look.

The costs of these displays are still pretty high. There is a fair amount of R&D work going on for using these displays as commercial movie theater screens. I think we're still quite a ways off from widespread use. But they would be perfect for custom applications, such as a cinema with a deep-curve screen. Projectors run into severe keystone issues trying to throw an image onto such a surface. A direct-view LED theater screen would have zero focus or keystone issues at all. MSG Entertainment is working on the MSG Sphere in Las Vegas. That venue may open next year. It could be revolutionary.

[Ned Weasel]

They're protesting the demise of Kmart and its Blue Light Specials.

[kphoger]

Update: did a bit of Googling and it appears that these are due to premature component failure from a batch of defective light fixtures. Many Kansas cities have reported them. It seems like the bigger cities have gotten all of their defective lights fixed.

Oh no, there are still plenty of them around Wichita...

[triplemultiplex]

Driving through Lincoln, Nebraska after dark on I-80 and I noticed they seemed to intentionally have blue lighting at every ramp gore.  The rest of the freeway lighting was typical white, but any time a ramp came in or went off, that light was blue. 

[Road Hog]

There is an intersection not far from where I live that's newly constructed. All four street lights on this corner are deep blue. Makes me wonder if this is intentional, because what are the odds of all four lights malfunctioning at once?

[Scott5114]

It's probably more likely, honestly–if all four were purchased at once, they're probably from the same production batch (and thus have the same faulty components).

[StogieGuy7]

There are a couple of interchanges along I-94/I-41 in southern Milwaukee County, WI that have the exact same thing and it's quite noticeable. In particular, the West Elm Road and Drexel Avenue exits have lots of truly blue LED streetlights.  I have wondered myself as to why WisDOT would install such stupidly inefficient lighting, when the rest of their LEDs (and those along I-94 in N IL) are white and work great.  Perhaps it's the same issue as mentioned here.

[amroad17]

There are a few along I-71/I-75 here in Northern Kentucky near the Mt. Zion interchange (178).  They appear a bit more purple than blue and are very noticeable.  It is the set of lights in this stretch: https://goo.gl/maps/ckDVcCJkv42fJ59f6

[US 89]

I have run across several purple LED street lights in Tallahassee as well as a handful of blue ones. Glad to hear this is most likely an error and not intended as they are really painful on the eyes late at night.

[kphoger]

There are a few along I-71/I-75 here in Northern Kentucky near the Mt. Zion interchange (178).  They appear a bit more purple than blue and are very noticeable.  It is the set of lights in this stretch: https://goo.gl/maps/ckDVcCJkv42fJ59f6

Yes, I think of them as purple rather than blue.

[Fredddie]

The City of Des Moines swapped out all of the street lights for LEDs a few years ago. There are a handful that are the cooler white that look bluish purple and they don't seem to be as effective as the yellow white temperature.

[jakeroot]

Last I checked, theres a ton of failed LEDs along the 405 through Renton, WA. They appear more purple to my eyes. WSDOT confirmed via Twitter:

https://twitter.com/wsdot/status/1577059810977406976