10 ms·

The Purple Streetscape

80 points by turtleyacht 3y ago

timeagain 3y ago
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.
- Cthulhu_ 3y ago
  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.
  - sandspar 3y ago
    If you're looking for examples of cities who use these techniques, look at the downtowns of Vancouver, Portland, Seattle, and San Francisco.
    - Chilko 3y ago
      Other examples include many cities outside of North America - e.g. in Switzerland, that have very different downtowns to your cherry-picked examples.
Animats 3y ago
I have an LED lightbulb which failed into purple mode.
- rickmode 3y ago
  To be pedantic, this would be violet. (Purple is a mix of red and blue light.)
  - JKCalhoun 3y ago
    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.)
    - card_zero 3y ago
      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.
      - _nalply 3y ago
        > 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.
teslabox 3y ago
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 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 https://www.phoenix.gov/streets/led
ranger207 3y ago
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
- alright2565 3y ago
  I'll do even better. The failed streetlight closest to their office is at 33.7858029, -84.3887389, only two blocks or 1500ft away.
thayne 3y ago
> 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.
- praptak 3y ago
  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.
- Terr_ 3y ago
  > 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?
  - thayne 3y ago
    Well it could, and probably should, be standaedized.
  - dreamcompiler 3y ago
    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.
- fdsafdsafdol 3y ago
mindslight 3y ago
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 ?
dreamcompiler 3y ago
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-for-safer-disinfection/ https://dsiac.org/articles/using-222-nm-ultraviolet-uv-light...

80 points by turtleyacht 3y ago

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.

Cthulhu_ 3y ago
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.
- sandspar 3y ago
  If you're looking for examples of cities who use these techniques, look at the downtowns of Vancouver, Portland, Seattle, and San Francisco.
  - Chilko 3y ago
    Other examples include many cities outside of North America - e.g. in Switzerland, that have very different downtowns to your cherry-picked examples.

Animats 3y ago

I have an LED lightbulb which failed into purple mode.

rickmode 3y ago
To be pedantic, this would be violet. (Purple is a mix of red and blue light.)
- JKCalhoun 3y ago
  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.)
  - card_zero 3y ago
    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.
    - _nalply 3y ago
      > 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.

teslabox 3y ago

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 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 https://www.phoenix.gov/streets/led

ranger207 3y ago

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

alright2565 3y ago
I'll do even better. The failed streetlight closest to their office is at 33.7858029, -84.3887389, only two blocks or 1500ft away.

thayne 3y ago

> 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.

praptak 3y ago
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.
Terr_ 3y ago
> 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?
- thayne 3y ago
  Well it could, and probably should, be standaedized.
- dreamcompiler 3y ago
  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.
fdsafdsafdol 3y ago

mindslight 3y ago

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 ?

dreamcompiler 3y ago

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