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Modern white LEDs are actually a blue LED behind a yellow phosphor mask that turns the light white. More power emmited in the blue side of the spectrum results

by ferongr 10y ago

Modern white LEDs are actually a blue LED behind a yellow phosphor mask that turns the light white. More power emmited in the blue side of the spectrum results in better efficiency, and the difference is significant.

gilgoomesh 10y ago
The only reason to do everything with a blue LED + phosphor is that it's smaller and simpler than an array of LEDs – particularly for small lights. Streetlights use arrays of LEDs anyway (to achieve appropriate brightness) so shouldn't have any problem using a mix of different colors.
- ferongr 10y ago
  The color reproduction of RGB white LEDs is terrible. You just have tree spikes in the spectrum were each LED emmits light.
  - adrianN 10y ago
    Street lighting isn't meant for photography though.
    - tempestn 10y ago
      There is value to having things look like the colour they actually are outside of photography. Think of the nice red dress turning brown in the article.
- colanderman 10y ago
  Mixing colors in the array would be horrific. The array is sparse enough that each LED casts a distinct shadow through foliage. This forms a unique lighting texture on the pavement. If each LED were randomly red, amber, green, you'd have wild colors all over the pavement. Single color is the way to go. And the broad spectrum produced by phosphor makes for better vision compared to the narrow spectrum of sodium or straight-LED lighting. IMO the best option would be phosphor + yellow or green LED.
maxander 10y ago
Would it be much harder to have an even-yellow-er phosphor mask that would turn the light orange?
- ferongr 10y ago
  It's a lot less efficient.
  - homero 10y ago
    My bedroom has philips led that claim to be the most efficient and they're warm white
jacobolus 10y ago
The “better efficiency” of privileging the blue light coming directly from the diode is oversold. At night, what happens is that directly visible blue lamps in your peripheral vision cause a severe adaptation response from your eyes (a kind of “oh hey, it’s daytime” misjudgement), which causes everything that isn’t directly lit to recede into dark shadow as the rods are swamped. You end up using mostly cone vision, where the blue part of the spectrum doesn’t really contribute to brightness response anyway, defeating the original purpose. Longer wavelengths don’t cause the same kind of adaptation, allowing the rod cells in the eye to remain useful down to much lower levels of overall environmental lighting. Industry has made up bogus metrics/arguments about “mesopic efficiency” of high-CCT street lamps and car headlamps which are IMO based more on marketing needs than dispassionate scientific investigation. I’m hoping that someday non-industry-funded color scientists will do some proper research on the glare and adaptation effects of different outdoor lighting sources.
- ferongr 10y ago
  Well, many transport authorities don't care and would rather save money on electricity costs and materials (less LEDs and less powerful drivers) than actually make the road more driveable at night.
  - jacobolus 10y ago
    They would save even more money on electricity by just cutting the brightness of the lamps. Whatever official body or industry recommendation sets the standards for urban illumination really needs to bring things down. My street’s new LED lamps could have their intensity chopped by 2/3 without adversely affecting anyone’s vision.
    - closeparen 10y ago
      The electorate believes that brighter street lighting leads to less crime, and dimmer street lighting leads to more crime. A municipal politician's career would be eviscerated by the first violent crime on a street they voted to dim. "Soft on light pollution" doesn't kill political careers.
ocschwar 10y ago
It's more efficient in the manufacturing phase (1 LED instead of 2 or three.) But a 3 LED RGB light can produce softer light, with more lumens per watt.
- mark-r 10y ago
  I believe the part about RGB producing softer light, but the higher efficiency is new to me. Do you have a source?
  - sp332 10y ago
    If you have a bluish LED, you can make it warmer by blocking some of the blue light. But this hurts the efficiency.
  - ocschwar 10y ago
    It's pretty much a set pattern through the whole electromagnetic spectrum: The longer the wavelength, the easier it is for manmade artifacts to produce it. All the way from AM radio to X rays. The shorter the wavelength, the harder the tradeoff between the expense of manufacturing the device and the cost of energy to use it. That's why if you were tinkering with electronics in the 90's, you watched how LED makers started with red, then made green ones, and what a big deal it was when the first blues came out. They were faint, and expensive. It took some time for them to become practical.
    - mark-r 10y ago
      I remember reading how rare and expensive blue LEDs were, then found one being used for the high-beam indicator in my 1985 Volkswagen. Made me wonder what all the fuss was about. It still doesn't answer my question about efficiency.

by ferongr 10y ago

gilgoomesh 10y ago

The only reason to do everything with a blue LED + phosphor is that it's smaller and simpler than an array of LEDs – particularly for small lights. Streetlights use arrays of LEDs anyway (to achieve appropriate brightness) so shouldn't have any problem using a mix of different colors.

ferongr 10y ago
The color reproduction of RGB white LEDs is terrible. You just have tree spikes in the spectrum were each LED emmits light.
- adrianN 10y ago
  Street lighting isn't meant for photography though.
  - tempestn 10y ago
    There is value to having things look like the colour they actually are outside of photography. Think of the nice red dress turning brown in the article.
colanderman 10y ago
Mixing colors in the array would be horrific. The array is sparse enough that each LED casts a distinct shadow through foliage. This forms a unique lighting texture on the pavement. If each LED were randomly red, amber, green, you'd have wild colors all over the pavement. Single color is the way to go. And the broad spectrum produced by phosphor makes for better vision compared to the narrow spectrum of sodium or straight-LED lighting. IMO the best option would be phosphor + yellow or green LED.

maxander 10y ago

Would it be much harder to have an even-yellow-er phosphor mask that would turn the light orange?

ferongr 10y ago
It's a lot less efficient.
- homero 10y ago
  My bedroom has philips led that claim to be the most efficient and they're warm white

jacobolus 10y ago

The “better efficiency” of privileging the blue light coming directly from the diode is oversold. At night, what happens is that directly visible blue lamps in your peripheral vision cause a severe adaptation response from your eyes (a kind of “oh hey, it’s daytime” misjudgement), which causes everything that isn’t directly lit to recede into dark shadow as the rods are swamped. You end up using mostly cone vision, where the blue part of the spectrum doesn’t really contribute to brightness response anyway, defeating the original purpose. Longer wavelengths don’t cause the same kind of adaptation, allowing the rod cells in the eye to remain useful down to much lower levels of overall environmental lighting. Industry has made up bogus metrics/arguments about “mesopic efficiency” of high-CCT street lamps and car headlamps which are IMO based more on marketing needs than dispassionate scientific investigation. I’m hoping that someday non-industry-funded color scientists will do some proper research on the glare and adaptation effects of different outdoor lighting sources.

ferongr 10y ago
Well, many transport authorities don't care and would rather save money on electricity costs and materials (less LEDs and less powerful drivers) than actually make the road more driveable at night.
- jacobolus 10y ago
  They would save even more money on electricity by just cutting the brightness of the lamps. Whatever official body or industry recommendation sets the standards for urban illumination really needs to bring things down. My street’s new LED lamps could have their intensity chopped by 2/3 without adversely affecting anyone’s vision.
  - closeparen 10y ago
    The electorate believes that brighter street lighting leads to less crime, and dimmer street lighting leads to more crime. A municipal politician's career would be eviscerated by the first violent crime on a street they voted to dim. "Soft on light pollution" doesn't kill political careers.

ocschwar 10y ago

It's more efficient in the manufacturing phase (1 LED instead of 2 or three.) But a 3 LED RGB light can produce softer light, with more lumens per watt.

mark-r 10y ago
I believe the part about RGB producing softer light, but the higher efficiency is new to me. Do you have a source?
- sp332 10y ago
  If you have a bluish LED, you can make it warmer by blocking some of the blue light. But this hurts the efficiency.
- ocschwar 10y ago
  It's pretty much a set pattern through the whole electromagnetic spectrum: The longer the wavelength, the easier it is for manmade artifacts to produce it. All the way from AM radio to X rays. The shorter the wavelength, the harder the tradeoff between the expense of manufacturing the device and the cost of energy to use it. That's why if you were tinkering with electronics in the 90's, you watched how LED makers started with red, then made green ones, and what a big deal it was when the first blues came out. They were faint, and expensive. It took some time for them to become practical.
  - mark-r 10y ago
    I remember reading how rare and expensive blue LEDs were, then found one being used for the high-beam indicator in my 1985 Volkswagen. Made me wonder what all the fuss was about. It still doesn't answer my question about efficiency.