What color are the street lights in your town? While an unfortunate few still suffer under one of the awful colors offered by vapor discharge lamps, like the pink or orange of sodium or the greenish-white of mercury, most municipalities have moved to energy-saving LED streetlights, with a bright white light that’s generally superior in every way. Unless, of course, things go wrong and the lights start to mysteriously change colors.
If you’ve noticed this trend in your area, relax; [NanoPalomaki] has an in-depth and surprisingly interesting analysis of why LED streetlights are changing colors. After examining a few streetlights removed from service thanks to changing from white to purple, he discovered a simple explanation. White LEDs aren’t emitting white light directly; rather, the white light comes from phosphors coating the underlying LED, which emits a deep blue light. The defunct units all showed signs of phosphor degradation. In some cases, the phosphors seemed discolored, as if they experienced overheating or chemical changes. In other LEDs the phosphor layer was physically separated from the backing, exposing the underlying LEDs completely. The color of these damaged modules was significantly shifted toward the blue end of the spectrum, which was obviously why they were removed from service.
Now, a discolored LED here and there does not exactly constitute a streetlight emergency, but it’s happening to enough cities that people are starting to take notice. The obvious solution would be for municipalities to replace the dodgy units Even in the unlikely event that a city would get some compensation from the manufacturer, this seems like an expensive proposition. Luckily, [NanoPalomaki] tested a solution: he mixed a wideband phosphor into a UV-curable resin and painted it onto the lens of each defective LED in the fixture. Two coats seemed to do the trick.
We have to admit that we have a hard time visualizing a city employee painstakingly painting LEDs when swapping out a fixture would take an electrician a few minutes, but at least it’s an option. And, it’s something for hobbyists and homeowners faced with the problem of wonky white LEDs to keep in mind too.
In my city the manufacturer was replacing some under warranty; however the problem was noticed after a significant number of units were installed and now there’s no money to pay for the time and effort to install.
By the way, a few minutes of time by an electrician on a street light is actually closer to 45 minutes + full labour costs. And there’s hundreds – thousands of lights to be replaced.
If it turns out somebody stole a secret recipe for the phosphor I’m going to laugh… (very much like the capacitor issue from years ago).
The hideous flickering blue city lights have to stop. It is a crime against beauty
Doesn’t seem to be as common, but I’m seeing purple tinged car headlights more frequently now too.
Some people do that on purpose. Osram has a line of “Cool Blue” headlights that have a blue filter painted over halogen bulbs.
The materials are cheap enough that any municipal employee could paint with a wide brush or an airbrush, covering the whole surface, in less than a minute. The bigger problem is that quick UV curing epoxy can’t be used in full sun, so a different formulation is necessary.
I remember the sodium lights. It gave off garish orange light that made everything seems monochromatic. Like you’re trapped in a B&W TV. I hated those and avoided going to store that used it if I was going to be there after dark. Fortunately they seems to have gone extinct from public use before 21st century rolled around, the only place I still see them is on old pictures used on web sites and on eBay as NOS bulbs.
USA. I guess the sodium light may still be in use in older places that hasn’t gone through remodel or upgrade.
On Big Island in Hawaii, they still use Low-pressure Sodium lights.
This is because of the telescopes on Mauna Kea.
Sodium light has only two narrow spectral lines ( 589.0 nm and 589.6 nm )
These are trivial to filter out.
LEDs or incandescents have too broad a spectral line.
Sodium vapor lamps produce less light pollution and don’t reduce ones natural low light vision as much. They are the better lamp.
One has to assume the ugliness is the point. Everything these people do seems to be centered around creating an uglier world
Thank you; I was wondering if a nearby town to me (UK) had blue streetlights deliberately or accidentally and now I know!
Ah, sodium street lights, how I miss you! Far superior to the painfully harsh and blindingly bright stark white modern lights.
Street lights have been like this where I live for years. The local uni colors are purple and white, so for a while we thought it was something “fun” the city did. Found out the truth later.