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Blue street lights in KS

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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?

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.

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.

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.


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