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I was asking this question about what LED's are beautiful (now closed as opinion-based) "Which LEDs are the most beautiful? [closed]", and I saw that there are "Lime" colored LEDs. Here is an example: LED LUXEON CZ LIME SMD. What are they used for?

I have shown in my answer one particular use for this color (and it does not appear to be common knowledge.) For that alone, this question is valuable, but I'm looking for any other uses of this interesting color.

Null
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MicroservicesOnDDD
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4 Answers4

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This specific color of LED is used to improve the Color Rendering Index (CRI), and round out the "richness" of some of the higher end color LEDs, some of which are used for stage lighting. (The following two images taken from here.)

enter image description here

As you can see below, the lime color rounds out the spectrum nicely:

enter image description here

It is interesting that the lime color is the only color to get two dies / chips. Perhaps it needs two dies because its spectrum distribution curve is so wide and it has to cover a lot more frequency-range.

MicroservicesOnDDD
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    this question and answer is more suitable for the photography SE – jsotola Feb 25 '22 at 05:48
  • @jsotola -- If I don't get an answer here, perhaps I'll try there, or the physics SE. Or chemistry. What would stage lighting be under? – MicroservicesOnDDD Feb 25 '22 at 05:53
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    you have an answer – jsotola Feb 25 '22 at 05:58
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    @jsotola - Sorry. I wanted to know more. I wanted to know what I don't know. – MicroservicesOnDDD Feb 25 '22 at 05:59
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    nobody knows all possible uses for green light ... start making a list, and invariably, someone will suggest a use that nobody else thought of – jsotola Feb 25 '22 at 06:03
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    such a question has nothing to do with electronics – jsotola Feb 25 '22 at 06:04
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    @jsotola, we'd all be happy to answer a question like, "what is a metal-film resistor used for?". Why should "what is a green LED used for?" be deemed, "nothing to do with electronics? " – GT Electronics Feb 25 '22 at 06:14
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    Exactly. Questioning the purpose of a common component is not a usage question as defined in the help files. Maybe it's opinion based, but that's about as opinion based as "what are zener diodes for". Just cause it's a part used by non-EE doesn't mean it's not an EE question. – Passerby Feb 25 '22 at 08:09
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    This should be marked as the answer :) The lime coloured LEDs are intended for high CRI light sources were a wide color spectrum is required - this is in oposition to just using a classic green LED (with red and blue) to generate white light. – Jakob Halskov Feb 25 '22 at 08:52
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    They're not 2 chips, they're blue LEDs with a phosphor, just like white LEDs are. That's why they're broad and why you see the ripples around 400-450nm in the OP's datasheet and in this older model more of a peak near 430nm. I only discovered this when I tried pulsing them on a timescale of 10s of ns. The phosphor is slower than that. The shape (asymmetry), as well as the width, of the phosphor peak is unusual. – Chris H Feb 25 '22 at 16:44
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    I agree, the answer to "What do lime LEDs do?" is "Fill gaps in light spectrum to create high CRI sources of light". Although our eyes can't see the difference in the white light, we can see the effect on colors of other objects. Consider the effect of a perfectly lime colored object (perhaps a lime) under the light source with and without the lime led present. – Phil Feb 25 '22 at 16:48
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    @MicroservicesOnDDD Here's a link to know one bit (of probably many) more: https://www.digikey.com/en/articles/lime-green-leds-encourage-color-tunable-lighting -- also, if I recall correctly, Philips Hue bulbs do use lime LEDs as a base color in a different color mixing method than RGB(W), creating a more natural-feeling light (can't seem to find a source for that, though). – orithena Feb 25 '22 at 16:48
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    This. See also https://electronics.stackexchange.com/questions/203264/why-are-the-three-component-leds-in-an-rgb-led-so-unbalanced/203273#203273 and https://electronics.stackexchange.com/questions/204998/why-are-there-only-rgb-and-rgbw-leds-but-none-with-more-chips-inside-one-housin for some backstory, and my speculation that LEDs like this would appear when the market was big enough for them. –  Feb 26 '22 at 12:46
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If the question was something like "What are the IR LEDs used for?" or "What are the uses for UV LEDs?" then you would get tons of scientific answers. Because IR, UV and some other special colour LEDs are indeed in use for specific purposes.

So you may have thought the same thing before asking a question about the possible uses of a lime colour LED. This is totally understandable.

However...

It appears that there's no specific use of lime colour LEDs but decoration. So it's possible that you may get some opinion-based answers. Maybe it has found a use in photography since this is quite a precise colour so might be required for better photography but, from what I've seen from Google Images, it is rather used for mostly decoration purposes such as,

  • Neon lights or fog lights for trucks/sports cars
  • LED strips inside/outside the buildings
Rohat Kılıç
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They do have scientific uses.

The group I'm in, for example, uses them to probe Rydberg excitons in Cu2O (cuprous oxide) (link to on of our papers in Phys. Rev. Materials). The phosphor output of the lime LED is an almost perfect match to the spectral region of interest, providing greater spectral intensity than a halogen source, with less undesirable above-bandgap exctation.

I'm sure we're not the only scientific users, because Thorlabs, a supplier of laboratory optics package and sell them from stock.

In general, any wavelength range is useful for some niche applications. This has been obvious for years with lasers, but now there's such a wide range of high-power LEDs we can applications for those too. In related experiments we also use amber and blue LEDs from the same series.

By the way, as I hinted above, these aren't made up of two emitters, but are a blue LED with a phosphor on top, like white LEDs. The phosphor is rather slow, and early datasheets weren't as clear as the latest ones, so we only discovered this when we tried to pulse them at a timescale of tens of ns. It's actually rather obvious if you think about the width and shape (asymmetry) of the emission band, which doesn't match a typical emitter.

Chris H
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  • This is exactly what I was looking for. Now I know a lot more about how they really work, as well as one more thing they are good for. I like knowing that they're slow, on a timescale of tens of ns -- Great! – MicroservicesOnDDD Feb 27 '22 at 21:09
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It is common on imaging sensors to use a Bayer Filter pattern where there are twice as many green sensors as there are blue and red sensors. If you are looking for a visible return of light on a standard camera sensor, it's useful to use the green spectrum because of this. One application of this is getting visible returns of light from retroreflective tape for target detection like on the aptly named Limelight Smart Camera (I am a volunteer mentor for a high school FRC robotics club, and that is how I ran across the limelight camera. I have no affiliation with the limelight camera and am not trying to promote it, but just mentioning it as a specific use case for lime colored LEDs)

I can't find any specific documentation that explicitly says that they are using lime colored LEDs because there are more green sensors than Red or Blue, but from my working knowledge of camera sensors it would make sense to use the color with the most sensors. You can't use a white light because you wouldn't be able to separate it from other background light sources, so you have to pick a specific light color source, so why not pick the one that has the most sensors on the camera.

TJR
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