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Comment by asdff | Hacker News Reader

Back when street lights were all sodium vapor, you could use a filter and eliminate a lot of light pollution. These days sodium vapor streetlight are being replaced by LED lights, that emit a white light and also frequently turn bright blue when they begin failing before long, and filtering out this source of light is no longer so simple.

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I fucking hate the blinding LED lights with a passion. Also, they fuck up the ecosystem in a major way. If we never get rid of them, they are visual DDT.

it's particularly obnoxious because LED lights can easily be made to be about the same place on the spectrum as the sodium vapor lights - it's just costs a few pennies more and has a slightly lower light efficiency so typical cheap short termism type thinking gets us the blue cold tone LEDS

Especially since at least the street lights are meant to light up the streets, not blind you. So the light efficiency is better, but the lighting efficiency is worse. It's not even short termism, it's wrong.

bluer lights actually do a way better job of being seen at night. if they're blinding that just means that they are too bright.

The large population of people who focus less clearly on blue light would beg to differ!

When visiting the Big Island of Hawaii I commented on the color of the street lights, which was unfamiliar. It was LED lights, but had a yellowish color IIRC.

I was told they were specifically designed to be easy to filter out by the telescopes on Mauna Kea, and used all over the island.

On a related note, can totally recommend visiting Manua Kea if you're in the neighborhood. We watched the sunset from the top of Mauna Kea and it was quite something.

Downward-facing, low pressure sodium lamps [1] used to be quite common in areas near major telescopes, as they are mostly monochromatic; for these, I don't think they were specifically designed for these areas, as much as they were an older lamp type that, when it was realized that newer lamps (eg, high pressure sodium) would be much harder to filter, ended up continuing to be used. It seems that, likely because there is so much experience developing methods to filter out light from LPS lamps, LED replacements have now been specifically designed to mimic them.

San Diego used to have many of these, apparently because of Palomar. There are a variety of arguments about safety and especially perception of safety that often leads to them being replaced with brighter, non-monochromatic lamps, though, depending on the political clout the telescopes have in the area.

[1] https://en.wikipedia.org/wiki/Sodium-vapor_lamp#Light_pollut...

There is no filtering of the led lamps possible, as they use phosphors to produce near continuum light. HPS at least had a collection of discrete lines you could avoid. LED lightning even taints 3nm wide emission line astronomy.

But astronomy can cope with light polution-- so long as it's relatively constant it can be calibrated out (leaving only its shot noise).

The human eye can't, but most people don't know what's been taken from them.

This was true of San Jose from the late 80s until recently, by agreement with UCSC / Lick Observatory. Not sure if it's still the case, and as the a peer comment says it was originally sodium lamps.

I thought I hated sodium yellow until LEDs became ubiquitous. They feel much harder to subconsciously tune out and draw my attention away from the road when driving much more than the old style. Maybe that effect will fade with time, but it hasn't happened yet.

Yup. Light pollution filters are practically useless now.

When I started observing 25 years ago, galaxies and nebulae were viable targets from my back garden, now I'm limited to solar system objects unless I load up my gear and drive a hour to my closest dark site.

I noticed that streets with LED lamps are far less visible from far away than ones with old "orange" street lamps. I can't imagine them being worse in terms of light pollution.

The difference is you used to be able to put a filter on the end of the telescope that blocks out all that orange, back when lights were mostly limited to the sodium emission spectrum.

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