171–180 of 218 posts
PS: I have an old friend whose dad still works at the Uranium plant in Oak Ridge. I told him that I was surprised that almost all of the facilities had been torn down, and he just looked at me straight in the face and said, “Who said it’s actually gone?” Noted.
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...And the old Engineer was just saying that that was the area on the spectrum they aimed for, so they found a light that emitted in that wavelength that could be technically implemented and scaled. Way better work than whoever it is handling this LED nonsense. Why we can't find a diode that we can use to simulate the old spectra would be a fun research project.
We of course can make LEDs of more or less any color. The current white LEDs are high-power blue LEDs that are covered by various phosphors to give a mix of colors for "full spectrum" illumination. Different color temperatures are produced by different mixes of phosphors. This is pretty similar to how the traditional luminescent (mercury vapor-based) lamps worked. But different phosphors have different efficiency and…
We can make LED light appear to be any given colour by mixing multiple LEDs. But mixed colour isn't the same as pure colour, made from a single spectra of light. Nor is it the same as true broad spectrum light - like we get from black-body radiation like the sun, or a tungsten bulb.
Its hard to tell the difference just by looking at a light. But different kinds of lights - even lights which look the same colour - will change what objects actually look like. And they probably have different effects on our sleep cycle and our low light vision. I was in a room once lit only by sodium vapour lights. The lights were yellow, but everything in the room (including me) appeared to be in greyscale. It was uncanny.
This is part of the reason why LED lights are still looked down on by a lot of old school photographers and film makers. Skin doesn't look as good under cheap LED lights.
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IDK if you've noticed but we are all lighting our house with bulbs that use 1/10th the amount of electricity as incandescents did. I like the color spectrum of a real lightbulb better, too, but not enough to pay 10x in power. I make up for it by using all kinds of random bulbs all over the place so that the aggregate light in the room fills more of the spectrum than if I coordinated them all to be the same.
Did you try using high CRI LEDs with color remperature of 2700K–3000K? When I switched from halogen to LED I did just that and the difference is not noticeable, you'll have the same yellowish tint and very natural looking colours. Even with expensive bulbs, extra longevity covers for higher cost.
The claimed extra longevity of LED bulbs has not materialized for me.
They seem to fail at roughly the same frequency that incandescent bulbs did in my home, which makes them about 10x to 15x more expensive.
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> that's why they were the color they were That doesn't seem right to me. Sodium (and mercury) vapor lamps are the color they are due to physics, and were chosen because they're very efficient (and long lasting). Low-pressure sodium is the best and worst of these; essentially monochromatic but fantastic efficiency. Their only advantage, color-wise, is that the light can be filtered out easily (they used to be widely…
The monochromatic light emitted from sodium lamps is also close to the peak sensitivity of the human eye. Colours are not distinguishable, but contrast is much enhanced compared to “cooler” light sources. *edit: but it’s the overwhelmingly larger lifespan (20-30k hrs) that led to the wide adoption as streetlights. And I guess, the same is true for the change to led today, because of less power consumption.
The low-pressure lamps emit monochromatic light and they have not only the advantage of long life but they are also the only other source of light that matches the energy efficiency of converting electrical energy to light of the LED lamps.
So replacing low-pressure lamps with LED lamps does not produce any significant economic effects, it was justified only by the supposed advantage of enabling color vision.
However in many places high-pressure sodium lamps have been preferred, which have a wider spectrum, so they allow some very poor color discrimination. The high-pressure lamps have a lower efficiency than LED lamps, so replacing them was justified by energy savings.
Outdoors at night, I prefer the monochromatic low-pressure sodium lamps, but sadly LED lamps have replaced them in most places.
Truly beautiful.
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The monochromatic light emitted from sodium lamps is also close to the peak sensitivity of the human eye. Colours are not distinguishable, but contrast is much enhanced compared to “cooler” light sources. *edit: but it’s the overwhelmingly larger lifespan (20-30k hrs) that led to the wide adoption as streetlights. And I guess, the same is true for the change to led today, because of less power consumption.
It's not especially close to the peak sensitivity of the human eye (in either bright or dim conditions), but that's entirely okay. The goal should be to not affect people's level of dark adaptation. If you use shorter ("bluer") wavelengths, as happens with white LEDs which consist of a blue LED + phosphor, it causes people's eyes to become bright adapted and effective night vision is ruined, causing people to have mu…
The sensitivity at sodium light is above 75% of the peak human vision (photopic) sensitivity.
This is a very small difference in light sensitivity. For example in the case of many sources of red light or blue light the sensitivity can be 5 to 10 times lower than the peak sensitivity.
Moreover, a perfect source of white light cannot achieve a better sensitivity than around 37%, i.e. less than half of the efficiency of an ideal source of monochromatic light at the sodium emission line.
Therefore the fact that currently LED lamps and low-pressure sodium lamps have about the same energy efficiency is caused by the LED lamps having a higher photonic efficiency and a lower threshold voltage (caused by a P-N junction voltage instead of the ionization potential of sodium), which compensate the disadvantage of using white light. A monochromatic LED lamp with the same color as the sodium lamps could have an energy efficiency at least double over the white LED lamps.
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I'm reminded of an article a while back talking about how the change from sodium streetlights to LED streetlights had a whole lot of unforeseen effects on animals, people's sleep patterns, driver awareness and visibility, etc. due to color changes. There was a comment on the article from an old civil engineer saying "no, these were not unforeseen, we actually did the research back in the day to figure out what color…
I'm sure tons of people along the way "noticed" but if you're selling LEDs or you're paid by the LED people to create marketing to convince people that LEDs are gonna save the planet, you're not gonna bring that up.
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It's not especially close to the peak sensitivity of the human eye (in either bright or dim conditions), but that's entirely okay. The goal should be to not affect people's level of dark adaptation. If you use shorter ("bluer") wavelengths, as happens with white LEDs which consist of a blue LED + phosphor, it causes people's eyes to become bright adapted and effective night vision is ruined, causing people to have mu…
> The goal should be to not affect people's level of dark adaptation. Wouldn't that be red light? But night scenes illuminated in red light have the side effect of looking nightmarish..
Yellow light a.k.a. amber light around the sodium emission line is a good compromise between energy efficiency, visual resolution and dark adaptation.