Street Lights turning Purple

[james_s]

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).

Stop guessing, we already know the answers. The failing lights were made by American Electric, it's a reputable brand. The drivers are not using a simple resistor and they're not using separate RGB LEDs, and they're not using through-hole LEDs, they're surface mount white power LEDs with a proper electronic driver and the phosphor layer is flaking off. This is already known, there is no need to speculate or make things up.

[MrMobodies]

Joke: Does that mean that they will illuminate thieves that have been sprinkled with smart water.

[Haenk]

https://www.businessinsider.com/led-city-streetlights-turning-purple-broken-tech-danger-2022-11?utm_source=digg

purple lights made it into mainstream media...

[Ranayna]

LED streetlights are weird...
I don't mind them as much in a car, at least after they have lost a bit of their initial brightness. When new they can be annoying point sources
My town was switches from CCFL tubes to LED during the last two years. The older ones are noticeably dimmer already. Is this degradation linear? If so, i wonder how long they will last.

But as a pedestrian, especially if there are tree branches under the light, the shadows the LEDs cast are, well, weird. All shadows are multiplied, since each LED throws it's own shadow, and if the branches are moving in the wind, the effect on the ground can be almost nauseating.

[AlbertL]

The manufacturer's web site offers this timely warning: https://www.acuitybrands.com/resources/trending-topics/low-quality-products

[james_s]

LED streetlights are weird...
I don't mind them as much in a car, at least after they have lost a bit of their initial brightness. When new they can be annoying point sources
My town was switches from CCFL tubes to LED during the last two years. The older ones are noticeably dimmer already. Is this degradation linear? If so, i wonder how long they will last.

But as a pedestrian, especially if there are tree branches under the light, the shadows the LEDs cast are, well, weird. All shadows are multiplied, since each LED throws it's own shadow, and if the branches are moving in the wind, the effect on the ground can be almost nauseating.

I'm not sure what the depreciation curve for LEDs looks like but I bet the manufactures have it available. I know that with fluorescent and metal halide lamps they depreciate pretty rapidly during the first 100 hours and then settle into a long slow decline. When they hit 70% of rated lumens they are considered end of life. IIRC rated lumens is the value after the first 100 hours.

I've found that LED street lights vary widely, some of them are almost point sources and have a lot of glare, others are much nicer. I like the white light much better than orange HPS but I don't like it as well as mercury vapor.

[AlbertL]

I saw one in July of last year in my area of Fairfax County, Virginia, and until recently hadn't seen any more.  But in the past month or so, I've seen a few.  Perhaps my electric utility bought most of their lights late in the run of bad units, so the failures are just beginning, or maybe the bad batch comprises a small percentage of their fleet.  I'm certainly not seeing the clusters of failures like some other parts of the country are.