The Purple Streetscape | Hacker News Reader

The Purple Streetscape

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80 pointsturtleyacht20 comments

This is a good write up about the LED street lights that fail by turning purple. I took a panoramic picture of purple streetlights in Phoenix recently: https://twitter.com/jamesknochel/status/1762862867861451027

I spoke with someone who worked on Phoenix’s streets department. Around 2015 they pulled all their high pressure sodium lights and replaced with 4000k led fixtures. After a while they did it again, replacing the 4000k leds with 2700k. They’re slightly less obnoxious than the 4000k fixtures, but inferior to ~2000k (almost blue-free) high pressure sodium bulbs.

The main advantage of LED fixtures over high pressure sodium bulbs is the LEDs were supposed to last 10 years, whereas the HPS bulbs have to be replaced every 5 years.

HPS bulbs are much better for safety, as our eyes work best with orange light under low-light conditions.

Edit: Phoenix’s page about their led conversion: https://www.phoenix.gov/streets/led

> let's talk about another common failure mode of outdoor LED lighting: flashing. LED lights use a constant current power supply (often called a driver in this context) that regulates the voltage applied to the LEDs to achieve their rated current. Unfortunately, several failure modes can cause the driver to continuously cycle.

This is a problem I've frequently encountered with household LED lighting.

What I don't understand is why modern houses aren't set up with a central, high quality "driver" with adequate cooling to convert AC to a steady DC current, then wire that to light outlets so you only need the LED itself there. That seems much more efficient, and cost effective than putting small, cheap drivers in every single bulb that fail after a few months or a few years.

A single current source for multiple receivers means the receivers have to be connected in series. This implies that the light switches would have to work as bypasses.

Also all LEDs would need to be rated for the same current.

> What I don't understand is why modern houses aren't set up with a central, high quality "driver" with adequate cooling to convert AC to a steady DC current

Perhaps to avoid a new extra set of nonstandard electrical wiring to much if not all of the home?

Well it could, and probably should, be standaedized.

12 gauge wire can easily handle the current needs of household LED lighting. Most modern houses in the US have 14 gauge. That can still be made to work.

The real reason -- as another commenter here said -- is that the lights would have to be in series and all must require the same current.

>What I don't understand is why modern houses aren't set up with a central, high quality "driver" with adequate cooling to convert AC to a steady DC current

This comes up fairly often here (because, after all, it isn't a hardware design forum), and the answer every time is - I^2 x R is a bitch. Losses increase with the square of current, instead of directly (as in the case of voltage). This is why it's significnatly more efficient to run power lines at high voltage, not high current. Running lighting circuits at LED voltage would require surprisingly thick cables to avoid losing most of the power in the cable runs.

On the other hand, it might make sense to create a 48v LVDC circuit, and regulate down from that at the point of load. This would avoid all of the issues with designing every single little LED bulb to handle 110v AC (or here, 240v AC), and the inevitable failure of the highly-stressed components.

There are a few people street lights near me in Seattle and now I probably know why. I thought it was a vain (!) attempt to deter intravenous drug use.

I did gather that's why some bathrooms have blue lights, but yeah, it wouldn't make much sense to have random street lights have that.

Drug policy ramble, it's proven more beneficial to offer clean, well-lit places to shoot drugs, along with mental & medical health personnel and free methadon.

If you're looking for examples of cities who use these techniques, look at the downtowns of Vancouver, Portland, Seattle, and San Francisco.

Other examples include many cities outside of North America - e.g. in Switzerland, that have very different downtowns to your cherry-picked examples.

Huh, TIL they're mostly made by one company, and that company is based in Atlanta. I knew about the problem because there's a failed streetlight near my office, which is apparently only about a mile down the road from Acuity

I'll do even better. The failed streetlight closest to their office is at 33.7858029, -84.3887389, only two blocks or 1500ft away.

222-nm UVC can supposedly disinfect COVID with much less harm to human tissue than adjacent frequencies, but it's still not available in an LED. Any light from an LED won't disinfect anything.

https://dsiac.org/articles/using-222-nm-ultraviolet-uv-light...

I don't know what the detour about sanitizing with UV LEDs was about, especially calling them "blue LEDs". UV leds most certainly exist, and not just the cheap barely-past-blue violet ones. I remember designing a product prototype using some, which I think were 320nm or 340nm, around the time that blue LEDs were the hot new thing. IIRC they were like $10 ea in small quantities, while blue LEDs were maybe $1 ?

I have an LED lightbulb which failed into purple mode.

To be pedantic, this would be violet. (Purple is a mix of red and blue light.)

More pedantic? I had an art teacher tell me purple isn't even a color — it's the name of a dye. (As you say, she said violet is the correct name.)

Violet is spectral: it's a frequency at the short end of the spectrum, and a shorter frequency than our blue cone cells are tuned to detect. So really it should appear dark blue, but in fact when we look at it the red cones, which are activated by long wavelengths, send some amount of signal too. This is due to a bug.

Purple, meanwhile, is a genuine mixture of short and long wavelengths, causing the same response.

> This is due to a bug.

I am fascinated by the quirk that our red cones also slightly perceive light beyond blue. Thanks to this quirk we can have the model HSV which wraps around the red hue to magenta and then blue. This is only possible because of this quirk.

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