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Comment by arcaster | Hacker News Reader

I wrote a paper for a sociology class in college focussing not only on light pollution, but the fact that many historians believe that certain cultural and aesthetic attributes of cities and surrounding urban areas are lost when the warm glow of HPS lights is replaced with stark white LEDs.

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If that's really a concern, LEDs don't have to be white.

Exactly this, I have seen "sodium" LED lights which replace HPS lights with a similar spectrum. Apparently this was to avoid replacing all of the lights at once, and by swapping them out as they burn out the city gets the full lifetime value of the bulbs. (yes the energy cost dwarfs that but not all cities want to front the upfront cost)

It's also helpful to have exterior LEDs that can change color on demand; for example, there are regulations in Florida on the coast as to what color lights you can use due to sea turtle nesting behaviors, but their nesting/mating is seasonal (and short window of time).

Kind of. The really high efficiency LEDs are blue. The problem is with the efficiency of green LEDs.

I suppose you could just use red and yellow LEDs and completely solve the circadian light problem. I think that such streetlights would be hard to sell.

You can cover the blue LEDs with yellow phosphor and get a subjectively "white" light, such as the Amazon Kindles. You could even cover that in a blue-reducing filter to make it much more yellow, but I don't know how bad the efficiency would be after all that.

> Kind of. The really high efficiency LEDs are blue. The problem is with the efficiency of green LEDs.

Hu? That's not true. Blue is less efficient, not more. The lower the wavelength the more efficient (toward the red side of the rainbow).

Also mono-color LEDs are MUCH more efficient than the ultraviolet ones with a phosphor (AKA white) ones.

If you wanted efficiency then have red and green in an LED, and that's it. You don't really need full color at night.

Each LED technology has an optimal wavelength. The current tendency is to use blue LEDs and then make white light with phosphors so the development is mostly on the blue LED technologies.

The green problem is caused by the lack of a technology. So you end up with bluish/green coming down from the blue side and yellowish/green when going up from the red side. That prevents really efficient RGB LEDs and makes the inefficient phosphor based white LEDs competitive. If you ever see a RGB LCD backlight you will see that there are more green LEDs than red or blue LEDs.

They don't. So why are so many municipalities installing the white ones, to the detriment of quality of life on residential blocks?

The same thing could have been said when we went from oil lamps to light bulbs.

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