# LED's for DUMMIES: High CRI ... Efficiency...



## jso902 (May 3, 2014)

*Why are high CRI LEDs less efficient than a regular LED? lumen per lumen...
Is it due to an extra tint that scales back an over powering wavelength to allow the less powered spectrum to be 'more' visible?
* 
LEDs typically emit in the blue-UV section.
Different Phosphor tints helps redirect energy to lower wavelengths that help fill in the light spectrum... But in the process, energy is lost to heat and some wavelengths reproduced will land outside of the visible spectrum. 
​


SemiMan said:


> High CRI LEDs use a red phosphor that generates a ton of light that is at >630nm and well past 700nm all where eye sensitivity is low to 0. This is essentially wasted energy.


To clarify, most of the heat is not from the LED, but is made from the driver/electronics behind the LED


TEEJ said:


> LED make mostly LIGHT, and the heat is not from the output, its from the process running the LED [,electronics], behind it. The BEAM is light.




*And if that's the case, why don't they just make 3 LEDs onto 1 die so they get the entire RGB spectrum like a computer monitor/tv?*

Multiple LEDs may cause shadowing effects that may not reflect well. However, there are multiLED lights that attempt to supplement a red hue to fill in the missing spectrum. But this only works with certain white LEDs.

*What role does an LED dome play? 
*
It helps direct the light. 

If the above is wrong, please let me know so it can be corrected.


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## Wooperson (May 3, 2014)

Hey jso902, 

White LEDs are blue or near-ultraviolet LEDs that have phosphorescent coatings on the dies (region that emits the light). These phosphorescent coatings look yellowish-white. How the coatings work is that they absorb light in the blue/near-UV wavelengths and "shift" those wavelengths to larger wavelengths; this process is called Stokes shift. Larger wavelengths of light have lower energy than smaller wavelengths such as blue/near-UV. Since high energy waves are shifted to low energy, larger wavelengths such as red, yellow, green, etc. that make up white, that energy has to be lost and transferred somewhere else. This is usually heat and other non-light emitting quantum effects. Low-CRI light sources usually have narrower or highly biased spectra that do not represent the smooth spectrum of blackbody (such as the sun (not exactly, but close enough) or incandescent filaments) light sources. This is because they use a phosphor coating that is simple and made of very few components that perform Stokes shift to only those sets of narrow/biased spectra. Now, if you are using more phosphor components to add more colors to the spectrum (higher CRI), you are not only diluting the phosphor that's already there, but adding many other phosphors. The dilution makes the color shifting more inefficient as you get less color intensity. Additionally, addition of more phosphor also increases loss due to more Stokes shifts occurring. The higher CRI lights have more reddish, high wavelength components in the spectrum. Since you are performing a larger Stokes shift, you are dissipating more energy. That's why it's more inefficient. 

Making an LED with three dies is an interesting idea, but it has a few problems. Manufacturing is more precise and difficult to do since you are handling three LEDs in the space of one. The second problem is that three light sources will cause three shadows of different tints. Unless your light source is as small as the pixels on the computer screen, you will get some ugly colored beam profiles.

I hope that clears things up for you.

-Woo


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## jso902 (May 4, 2014)

Holy smokes. I had to read that several times before I understood what you said. And I'm kinda embarrassed to know so little about something I use everyday... Ie flashlights, TV's, laptops, 

Having said that, are all xpg leds the same with different domes? (I.e tint/bins)?
If domes determine the color, is that why there is an aura around the hot spot of my light?
If so much energy is lost to heat, why don't we move the tint/dome further away from the emitter? Or use lens filters instead?
And if what you said about led spectrum is true, are modifiers removing the dome exposing a UV hazard?


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## TEEJ (May 4, 2014)

jso902 said:


> Holy smokes. I had to read that several times before I understood what you said. And I'm kinda embarrassed to know so little about something I use everyday... Ie flashlights, TV's, laptops,
> 
> Having said that, are all xpg leds the same with different domes? (I.e tint/bins)?
> If domes determine the color, is that why there is an aura around the hot spot of my light?
> ...




The domes don't dictate the differences, they distribute what IS emitted....and aspects of that distribution impact some of those factors. (IE: You are focusing on domes instead of phosphors, confusing the issues)

The primary differences in tints, etc, are from the phosphors used.

So, for example, you would not have all xpg be the same with different domes, you'd have them all have the _*same domes, and different phosphors*_.


The energy lost to heat is mostly from the electronics themselves, so you'd be moving the wrong part. (Again, the dome is not the important part) IE: You protect the LED by drawing heat away from the electronics, using heat sinks, fins, or whatever helps remove head from that part of the flashlight. The dome has ZERO to do with the heat management or effects of heat. Remember, the LIGHT from the LED is NOT the hot part, the electronics BEHIND the LED is the hot part.

*Primary heat issue concept to get:* For an incandescent light bulb, almost ALL it makes is heat, with a small amount of light...so, MOST of the energy put into an incan bulb is emitted as infrared radiation, with a small percentage being visible light. That means its mostly heat not light, and, the beam itself IS the hot part. For an LED, its MOSTLY making LIGHT not heat, so *the BEAM is not what's hot, its the electronics behind the LED*.



The phosphors are what are shifting the UV to visible light, not the dome (Again, focus on the phosphors, the dome is not important, and, not protecting from UV, as the UV was converted to visible light by, yes, the phosphors...and, so, no, there's no real UV hazard from de-doming)


IE: The color, tint, CRI, are from the phosphors.

Energizing the phosphors uses energy...so, for any juice that flows INTO the LED, LESS LIGHT comes out, because MORE of that juice was used to make more phosphors emit the light at the desired wavelengths. The more you change the CRI, by using more phosphors, the less efficient the LED is at EMITTING light.

So, to get a higher CRI, you lose efficiency, lumens and cd, for any given drive level. (Its more efficient to produce some wavelengths, and less efficient to produce others....)


The "aura" around the hot spot is called the corona, and, its not because of the LED, its because of the way a reflector focuses a beam.

If you've ever played pool, or had to ricochet something, you've possibly noticed that things tend to bounce in complimentary angles...IE: They bounce off at the same angle they impacted at.....straight down gives straight back up (Dribbling a basketball), if you bank a pool shot off a bumper, if you impact the bumper at 15º, the ball bounces off it 15º to the other side, etc....And, when an LED, or bulb, etc, emits light, inside of a reflector bowl, the light is not ALL from the exact same POINT in space, its emitted across the entire surface of the LED.

SOME of the light will be emitted from a point on the LED that ricochets exactly dead center of the beam, and, as you move farther from that perfect spot on the LED, SOME of the light emitted will be LESS perfectly focused, and, NOT be centered in the middle of the beam. The light that's missing the perfect focus, but still gathered by the reflector and sent down range, has the best focused light in the middle, with a donut of less focused light around it. There will also be some light that missed the bowl entirely, and was not focused at all, it just spilled out of the bowl w/o hitting the reflector at all. THAT light is called the spill.

So a normal beam is composed of a hot spot in the middle, surrounded by a corona, with some spill outside of the focused beam.

This is NOT an artifact of the LED per se, in that all LED, bulbs, etc, form this pattern due to the REFLECTOR. (The SMALLER the LED, the easier it is to have MOST of the light it emits come from a point in space closer to perfect focus, and, that's a primary reason a smaller LED can throw farther for the same lumen output....the light is easier to focus. This concept is also referred to as apparent surface brightness, as the reflector "Sees" more light coming from a smaller surface, so, for the same lumens, its going to have higher lux.

Part of a dome's function is to distribute the light emitted by the LED, so it hits the reflector in a way that they thought would appeal to users.

The primary reason that modders REMOVE the dome, is because they want a tighter beam, to throw farther, and NOT the broader beam that the light's maker thought the general public would want. Losing the dome tends to reduce the flashlights' published lumens, which the marketing departments are loathe to do...as the general public has no clue what lux is. Removing the dome increases the apparent surface brightness of the LED, which increases the light emitted closer to perfect focus for the hot spot, but, which reduces the peripheral light that counts towards total lumen output.


The "Hole in the middle of the beam" pattern you see with a poorly focused beam, is typically the shadow of the emitter, as that requires a HOLE in the bowl (The emitter sticks out into the reflector through that hole...). A well focused beam refocuses light to fill in that hole, centering the hot spot in the center of the beam.








I hope this is a starting point for you to get a handle on the concept, and, let go of the dome-based misconceptions.


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## SemiMan (May 4, 2014)

Stokes losses are only part of the issue and not the biggest issue. The biggest issue is that the extra phosphors emit in the red to even infrared, wavelengths where the eye has low or no sensitivity.

A common technique is to mix a red led with a special white to achieve high CRI. The red led is less efficient than the blue pump led for the white, but the emitted light is at a wavelength of good eye sensitivity. Alternate narrow band red phosphors are also being developed for the same benefit.

Semiman


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## TEEJ (May 4, 2014)

SemiMan said:


> Stokes losses are only part of the issue and not the biggest issue. The biggest issue is that the extra phosphors emit in the red to even infrared, wavelengths where the eye has low or no sensitivity.
> 
> A common technique is to mix a red led with a special white to achieve high CRI. The red led is less efficient than the blue pump led for the white, but the emitted light is at a wavelength of good eye sensitivity. Alternate narrow band red phosphors are also being developed for the same benefit.
> 
> Semiman



True dat. 

:thumbsup:


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## Wooperson (May 4, 2014)

SemiMan said:


> Stokes losses are only part of the issue and not the biggest issue. The biggest issue is that the extra phosphors emit in the red to even infrared, wavelengths where the eye has low or no sensitivity.
> 
> A common technique is to mix a red led with a special white to achieve high CRI. The red led is less efficient than the blue pump led for the white, but the emitted light is at a wavelength of good eye sensitivity. Alternate narrow band red phosphors are also being developed for the same benefit.




If the phosphors emit in wavelengths that we can't see, then it's correct that it's another sort of inefficiency in terms of what's visible and what's not. However, the main causes of inefficiency is still Stokes shift since there is a wavelength shift. Phosphors that emit light in invisible wavelengths are largely useless :fail:, but I don't think most LEDs have the problem of emitting in invisible wavelengths. 

The red-mixing you talked about is usually a red LED that's supplementing the larger wavelengths which are usually missing from most low CRI LEDs that appear bluish. If red LEDs are used (or any LED without wavelength shifting), it is actually more efficient since there is no wavelength shifting and all produced light is emitted without losses. Our eyes see the full intensity. This is what Philips does with their "L-Prize Award Winning" bulbs. Not sure what you mean by mixing red LEDs with special white, but the closest effect is the anti-Stokes shift that's due to absorption of a lower energy wavelength and emission at a higher wavelength. This process requires the removal of energy from the environment and isn't common (if not unavailable) in LEDs.


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## Wooperson (May 4, 2014)

jso902 said:


> Holy smokes. I had to read that several times before I understood what you said. And I'm kinda embarrassed to know so little about something I use everyday... Ie flashlights, TV's, laptops,
> 
> Having said that, are all xpg leds the same with different domes? (I.e tint/bins)?
> If domes determine the color, is that why there is an aura around the hot spot of my light?
> ...




Haha, sorry if I answered with too much detail. Don't be embarrassed! 

TEEJ's response about the dome is correct.


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## SemiMan (May 4, 2014)

Sorry but your answer is wrong. Stokes losses are an issue but the predominant loss is not radiometric I.e. stokes losses but photometric I.e. perceived brightness.

As blue LEDs are significantly more efficient than red LEDs especially at higher temps, a blue pumped narrow red phosphor can be more efficient than today's red LEDs ... Hence the research stokes losses and all. 

You can't just mix any old white with red for best CRI. You need a special white that is above the black body as the red pulls it down.

Phosphors with QE >1 are possible but rare.


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## Wooperson (May 4, 2014)

SemiMan said:


> Sorry but your answer is wrong. Stokes losses are an issue but the predominant loss is not radiometric I.e. stokes losses but photometric I.e. perceived brightness.
> 
> As blue LEDs are significantly more efficient than red LEDs especially at higher temps, a blue pumped narrow red phosphor can be more efficient than today's red LEDs ... Hence the research stokes losses and all.
> 
> ...




If the phosphors release light in a limited, visible wavelength range, then the most significant losses must be due to losses before emission from the LED. If you are presuming that the LED emits in an invisible spectrum, then that would lead to more visual inefficiency. Of course, making such an LED wouldn't make much sense in the first place. Perceived brightness matters less if you are getting less light in the first place due to an inefficient phosphor. The perception sensitivity of light follows a Gaussian-looking plot centered around green. The eyes are more sensitive to reddish wavelengths than bluish wavelengths ("Human eye sensitivity and photometric quantities" Schubert of RPI). Therefore, if you are looking at a white light source with very little ultra-blue and infra-red wavelengths, perception intensity shouldn't matter as much since retinal ganglion cells will normalize their firing frequencies so that neighboring regions are not overly stimulated by different wavelengths; therefore you don't get much perception differences as compared to intensity differences due to Stokes losses. 

Red LEDs are significantly more efficient. Cree cites their minimum red output as 45.7 lm/350 mA compared to a minimum of 30.6 lm/350 ma for blue LEDs. Maxima show the same trend with 73.9 lm/350 mA for red and 39.8 lm/350 mA for blue. (Cree XP-E data sheet, Cree, 2013). Lumileds also states that their efficacy is 72 lm/W for red LEDs and 37 lm/W for blue leds (Lumileds "All in 1 LED lighting solutions guide"). A blue pumped red phosphor is still going through a conversion of wavelengths so it cannot possibly be more efficient than a die that only releases in a certain wavelength. More conversion usually results in more intersystem crossing and other quantum losses. 

Our eyes cannot detect light phase shifts, but can only detect the final superposition of light. That's why we can't differentiate different color waves combined into one unless there is a shadow. The emission spectrum can't be "pulled-down" by a red LED, the red can only supplement and fulfill the larger wavelength emission spectrum. Shifting spectra only happens if there is some sort of absorption/emission phenomena. Pumping blue light to get red wavelengths is counterintuitive for higher efficiency since you have to shift and therefore dissipate the lost energy (as stated above). Therefore, you can actually mix red-emitting phosphors for a higher CRI since our eyes can't tell the difference. That's why many high CRI bulbs do that and include both red and blue LEDs. The blue usually takes advantage of the phosphor layer. Other LEDs just include a red phosphor because it's simpler to manufacture, but there is a reason that the multi-color LED designs usually win efficiency prizes.


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## TEEJ (May 4, 2014)

Um, fellas, look at the OP.

I think a more basic discussion - for this thread at least, would help him better. 

The poor guy asked what time it was, and you guys are going into the metalurgy of clock springs.


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## Wooperson (May 4, 2014)

LOL yeah, sorry jso902. Good point, TEEJ. I realized I'm not answering OP's question and rather doing literature search. I'm gonna go do something else now...  I think the material in this thread answers OP's questions pretty well and will continue answering for eternity.


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## TEEJ (May 4, 2014)

Wooperson said:


> LOL yeah, sorry jso902. Good point, TEEJ. I realized I'm not answering OP's question and rather doing literature search. I'm gonna go do something else now...  I think the material in this thread answers OP's questions pretty well and will continue answering for eternity.



I just noticed you're in Philly. I'm over the river in Lawrenceville.

Are you going to the Photon Fest?


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## Wooperson (May 4, 2014)

I'm over at the University of Pennsylvania and I might be busy, but I'm definitely interested. Do you know where I could learn more about it?


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## TEEJ (May 4, 2014)

Wooperson said:


> I'm over at the University of Pennsylvania and I might be busy, but I'm definitely interested. Do you know where I could learn more about it?



Its May 31, in Califon, NJ. (A Saturday)

Follow this thread:

http://www.candlepowerforums.com/vb...ashaholic-Get-Together-NJ-NY-PA-CT-Area/page9


At the end of this thread will be the start of a new thread to go to for THIS Photon Fest (The end of the last thread is used to give notice of the next one)


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## Wooperson (May 4, 2014)

Thanks, I'll definitely look into it!


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## SemiMan (May 4, 2014)

Wooperson said:


> If the phosphors release light in a limited, visible wavelength range, then the most significant losses must be due to losses before emission from the LED. If you are presuming that the LED emits in an invisible spectrum, then that would lead to more visual inefficiency. Of course, making such an LED wouldn't make much sense in the first place. Perceived brightness matters less if you are getting less light in the first place due to an inefficient phosphor. The perception sensitivity of light follows a Gaussian-looking plot centered around green. The eyes are more sensitive to reddish wavelengths than bluish wavelengths ("Human eye sensitivity and photometric quantities" Schubert of RPI). Therefore, if you are looking at a white light source with very little ultra-blue and infra-red wavelengths, perception intensity shouldn't matter as much since retinal ganglion cells will normalize their firing frequencies so that neighboring regions are not overly stimulated by different wavelengths; therefore you don't get much perception differences as compared to intensity differences due to Stokes losses.
> 
> Red LEDs are significantly more efficient. Cree cites their minimum red output as 45.7 lm/350 mA compared to a minimum of 30.6 lm/350 ma for blue LEDs. Maxima show the same trend with 73.9 lm/350 mA for red and 39.8 lm/350 mA for blue. (Cree XP-E data sheet, Cree, 2013). Lumileds also states that their efficacy is 72 lm/W for red LEDs and 37 lm/W for blue leds (Lumileds "All in 1 LED lighting solutions guide"). A blue pumped red phosphor is still going through a conversion of wavelengths so it cannot possibly be more efficient than a die that only releases in a certain wavelength. More conversion usually results in more intersystem crossing and other quantum losses.
> 
> Our eyes cannot detect light phase shifts, but can only detect the final superposition of light. That's why we can't differentiate different color waves combined into one unless there is a shadow. The emission spectrum can't be "pulled-down" by a red LED, the red can only supplement and fulfill the larger wavelength emission spectrum. Shifting spectra only happens if there is some sort of absorption/emission phenomena. Pumping blue light to get red wavelengths is counterintuitive for higher efficiency since you have to shift and therefore dissipate the lost energy (as stated above). Therefore, you can actually mix red-emitting phosphors for a higher CRI since our eyes can't tell the difference. That's why many high CRI bulbs do that and include both red and blue LEDs. The blue usually takes advantage of the phosphor layer. Other LEDs just include a red phosphor because it's simpler to manufacture, but there is a reason that the multi-color LED designs usually win efficiency prizes.



At first I thought you knew what you were talking about but rereading what you wrote shows a lack of understanding. Quoting and compiling from Wikipedia and other sources does not make you knowledgeable.

You stuck your foot in your mouth when you used lumens to discuss efficiency of red and blue LEDs. Lumens is useless for that discussion. Blue LEDs are far more efficient than 620-630nm LEDs and so yes blue pumping a narrow red phosphor makes a ton of sense and hence why many companies are working on narrow red phosphors (and green).

You changed feet when the tried to explain how adding in red would not pull down the white point. Seems you are not familiar with blackbody curves and 2d color spaces.

So ... As previously stated. High CRI LEDs use a red phosphor that generates a ton of light that is at >630nm and well past 700nm all where eye sensitivity is low to 0. This is essentially wasted energy. Red LEDs in higher CRI bulbs are narrow spectrum emitters and emit where the eye us fairly sensitive. They are not very efficient radiometrically especially when hot, but the spectrum is all "useful", no wasted energy.


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## SemiMan (May 4, 2014)

TEEJ said:


> Um, fellas, look at the OP.
> 
> I think a more basic discussion - for this thread at least, would help him better.
> 
> The poor guy asked what time it was, and you guys are going into the metalurgy of clock springs.



Agreed but unfortunately an answer provided while useful to the argument was wrong in its conclusion


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## jso902 (May 4, 2014)

Woah! LoL...I don't mind the extra info... 
Let's see if I understand this correctly...
LEDs classically emit in the blue-UV section.
Different Phosphorus tint helps redirect energy to lower wavelengths that help fill in the light spectrum... But in the process, energy is lost to heat and some of the wavelengths overshoot into the IR spectrum. 

So... What's the point of the dome? And why do I hear people talk about tint shift when a person removes it?
When you say distribute it, is that directing the light? I.e flooding the LED?

The blue / red confuses me a little. 
1. I'm surprised LEDs are more efficient to the higher light spectrum. Is this because phosphorus's valence electron shell is higher? ( i.e. shorter fall from one valence level and producing higher frequencies?)

2. My understanding of red vs blue perception is that red was a lower frequency and required less energy to increase intensity while blue required substantially more energy to be more visible.


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## Wooperson (May 4, 2014)

Yes, the first part is correct! However, overshoot is one thing manufacturers try to avoid since overshooting into the invisible wavelengths is pointless for illumination. 

The dome acts as a lens that directs the light in a preferable pattern. For example, surface mounted LEDs are more useful if light is emitted in one direction and away from the electronic circuit components nearby. The dome focuses the light so that it projects forwards and away from the board which the LED is mounted on. If you remove the dome, you don't get this focus so light spreads out in all directions that the LED die faces. 

Removing the dome essentially removes another material the light has to pass through. The tint shift occurs due to a few reasons, but the major reasons I can see are that different wavelengths are focused differently by the dome (some color waves are bent more so than others as light moves from one medium to another) and some wavelengths reflect at different angles within the dome. When you remove the dome, you change how different wavelengths of light are focused so you get some perceived changes in tint in the beam. What the exact effects are, I'm not totally sure. 

Also: 
1. Lower wavelength light such as blue are higher in energy and requires electrons to be raised to a higher energy level. This requires more energy input to do per electron. Red is lower energy so electrons don't have to be raised to such a high energy level as blue. Therefore, you can raise more electrons to a level that emits red light than blue light with the same amount of electrical energy.

2. Yes, that's true. Our eyes are more sensitive to reddish wavelengths than bluish wavelengths. Therefore, you need more blue to be as visible as red.


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## Wooperson (May 4, 2014)

jso902,

One more thing that I should clear up. I think SemiMan means that you can't compare lumens as absolute energy output efficacy because lumens are adjusted to how our eyes perceive light, not absolute energy output. I thought that's what SemiMan was comparing because he keeps on referring to what's visible or not, so that's why I compared the different colors in terms of lumens. I think he's focused more on what wavelengths we can see more than quantum efficiency (absolute light energy emitted) which was what I was getting at. 

to sum up what I think is causing confusion: visibility efficiency and absolute energy efficiency are different things


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## Wooperson (May 4, 2014)

jso902, sorry about this, but I think I'm going to stop interacting with this thread. I'm trying to help you by writing about what I know due to working with fluorescent compounds, semiconductors, and optics at school. However, what I'm saying may be true theoretically, it may not be 100% true for LEDs judging by the responses I'm getting here (although I'm sure most of it is supported). Instead of getting detailed reasons that I can learn from, I'm just getting rehashed facts and statements saying that everything I know is wrong. Feel free to PM me, bro.


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## TEEJ (May 5, 2014)

jso902 said:


> Woah! LoL...I don't mind the extra info...
> Let's see if I understand this correctly...
> LEDs classically emit in the blue-UV section.
> Different Phosphorus tint helps redirect energy to lower wavelengths that help fill in the light spectrum... But in the process, energy is lost to heat and some of the wavelengths overshoot into the IR spectrum.
> ...




Your references so far, have a lot of google fu kata elements....referencing valences indicating a deeper knowledge of how a phosphor might emit a photon when excited, albeit with other references indicating that you don't know how that works, etc....so, I am trying to fill in the gaps for you, as you are obviously giving this the old college try as far as doing your own research. That can be frustrating for you when there are so many background issues involved.



The dome primarily spreads the photons out so more of them hit the bowl of the reflector and end up being sent out as lumens. There are sometimes refractive index and even some yellow doping stuff, etc, going on too, but, in light of this thread's context, lets stick to the important parts.

LED do not really make much UV, and, it gets EXPENSIVE for example to make LED that emit strongly in the UV spectrum, say lower than ~ 390 nm....albeit the violet and purple end of things is super well endowed (So if we call 390 nm and shorter "UV", the LED itself is emitting mostly above that in "Near UV" territory, up to "blue" depending on the LED type... The phosphors are to make it less "Angry Purple", as they take that light, and emit more of the rest of the visible spectrum.

The process is not what is really making the heat, again, its not the LIGHT, its the electronics making the most heat.

IE: The "Process of converting angry purple to nicer lumens" doesn't create heat by over shooting and making IR, it created heat because its an electronic device, and the heat is being generated primarily beneath the LED, and the side not involved with light production.



The phosphors work about the same as they do in a fluorescent bulb, etc....and, you've perhaps touched a lit fluorescent tube and noticed that the tube itself is not really that hot, its just the ends and the ballast that are hot. (The electronics, not the emission of light itself)

Another point: PHOSPHOROUS ≠ Phosphor

IE: Phosphorus is not a phosphor. So "different phosphorous tints" is not the same thing as saying "different phosphors". (Hitting phosphorous with light doesn't excite it, we are just using the root word, which is part of what we are really using, not the chemical per se. We can set phosphorous on fire, and it can burn, but, it doesn't fluoresce, and we don't have different tints of it, etc...)



Another concept: The lumen output, and the photon output, are related, but not in lock-step. "Lumens" are a weighted scale, with some frequencies having more weight due to how much our eyes love'm. Photons on the other hand are just sent whizzing out at various wavelengths, and they just don't give a rat's borro WHAT we call them.

So, MAKING photons does take energy - and the fluorescence of the phosphors, the electronics, etc...are where that energy went into. Once the LED is excited though, the electronics are cranking at whatever rate they are driven at, and photons are flying regardless of the wavelength.

The "Blue Light Specials" make a lot of blue, but, the lumens scale doesn't reward it as much as it rewards green/yellow borders. Same with yellow/red borders, the lumen scale doesn't reward the LED as highly as it would with more centered on our eye's favorite candy. (~ 555 nm)

So, the more of an LED you use up with phosphors to make it "warmer", the less you have for that yummy green eye candy. 

So, the warmer you make the LED, the lower the lumens.

Now, since our eyes REALLY DO see other parts of the spectrum better, we can't see as well when forced to use the other parts of the spectrum, so, we DO need more of that frequency band to actually resolve equivalent details.

So, if we make the LED powerful enough, or just stand closer to what we want to see, we can take advantage of that warmer LED's emissions, and see stuff.


So its not JUST that its more energy to make red than green, that's just a question of picking something that gives off that wavelength when excited enough, its also about the eye needing more of it to resolve equivalent details about what's going on out there. (More energy is needed to make ENOUGH red to be able to SEE ENOUGH with it)



Makes sense?


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## SemiMan (May 5, 2014)

Wooperson said:


> Yes, the first part is correct! However, overshoot is one thing manufacturers try to avoid since overshooting into the invisible wavelengths is pointless for illumination.
> 
> The dome acts as a lens that directs the light in a preferable pattern. For example, surface mounted LEDs are more useful if light is emitted in one direction and away from the electronic circuit components nearby. The dome focuses the light so that it projects forwards and away from the board which the LED is mounted on. If you remove the dome, you don't get this focus so light spreads out in all directions that the LED die faces.
> 
> ...



Overshoot? ... what the heck? Are you just making this stuff up?

The dome, in 90% of illumination LEDs is NOT for focusing. It is to improve extraction efficiency by ensuring as close to a perpendicular exit angle for as many of the light rays as possible hence no internal reflection.


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## SemiMan (May 5, 2014)

Wooperson said:


> jso902,
> 
> One more thing that I should clear up. I think SemiMan means that you can't compare lumens as absolute energy output efficacy because lumens are adjusted to how our eyes perceive light, not absolute energy output. I thought that's what SemiMan was comparing because he keeps on referring to what's visible or not, so that's why I compared the different colors in terms of lumens. I think he's focused more on what wavelengths we can see more than quantum efficiency (absolute light energy emitted) which was what I was getting at.
> 
> to sum up what I think is causing confusion: visibility efficiency and absolute energy efficiency are different things



Wooperson, JUST STOP. You obviously have no clue what you are talking about and are using Wikipedia to try to make yourself look intelligent yet have no understanding of what you are reading or writing. It is starting to get tiring.

Quantum Efficiency has nothing to do with absolute light energy emitted, PERIOD. That is just wrong. Quantum efficiency would only related to photons created. Radiometric energy is the right term!

You didn't "think" that was what I meant because you had no clue what I meant and you compared the colors in terms of lumens because you did not know that lumens were not the right measurement to use.

NOTHING is causing confusion except you. You are the one confused and posting erroneous information.


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## TEEJ (May 5, 2014)

SemiMan said:


> Overshoot? ... what the heck? Are you just making this stuff up?
> 
> The dome, in 90% of illumination LEDs is NOT for focusing. It is to improve extraction efficiency by ensuring as close to a perpendicular exit angle for as many of the light rays as possible hence no internal reflection.



I think its clearer to say its so more light hits the reflector bowl and is sent out as lumens. (If they could understand the context and perpendicular exit angles, etc, they would not be asking the other questions, etc...we need to make this basic)




Again, I think we should stick to the OP's quest.

Woo has indicated that he's withdrawing from the thread.


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## SemiMan (May 5, 2014)

As there is no reflector bowl on most modern high powered LEDs, then it does not make it clearer to discuss it. The dome is all about getting near perpendicular exit angles so you don't get internal reflections. That is pretty easy to understand.


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## TEEJ (May 5, 2014)

SemiMan said:


> As there is no reflector bowl on most modern high powered LEDs, then it does not make it clearer to discuss it. The dome is all about getting near perpendicular exit angles so you don't get internal reflections. That is pretty easy to understand.



The flashlight has the bowl, not the LED.


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## jso902 (May 5, 2014)

SemiMan said:


> Overshoot? ... what the heck? Are you just making this stuff up?
> 
> The dome, in 90% of illumination LEDs is NOT for focusing. It is to improve extraction efficiency by ensuring as close to a perpendicular exit angle for as many of the light rays as possible hence no internal reflection.



Dome topic: wait a minute... if i'm reading this correctly, the dome is to prevent the exited light from bouncing from a reflector back to the LED??? I'm assuming i'm reading this wrong, but i can see the idea being reasonable.

Back to my light topic: My fu ka google stuff is the limited information i recollect from highschool and the tid bits from college almost 15 years ago.
I tried to read wiki's LED topic and it went over my head. Hence all the questions. 
My understanding of light comes from the emitted light generated from an energizing electron falling from one valence shell down. 
e.g. Halogen light, you push energy into halogen's electron, the electron hops to a higher shell, then when it falls back down, it'll generate the light that we see. 

Perhaps my word choice was poor. I used overshoot as to describe the energy pushed into the longer wavelengths can't all hit the perfect red spectrum and some go into the lower frequencies i.e. IR and microwave spectrum. Like a bell curve. Is that incorrect? 

As for the information from, Woo, I do appreciate his input. I encourage it because I'd like us all to understand a little more about LED's; and to understand it correctly.


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## inetdog (May 5, 2014)

Halogen lights emit black body thermal radiation from their filament.
The chemical reaction with the halogen gas has nothing to do with emitting light and everything to do with scavenging metal boiled off the filament onto the envelope and returning to the filament.


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## jtr1962 (May 5, 2014)

jso902 said:


> Dome topic: wait a minute... if i'm reading this correctly, the dome is to prevent the exited light from bouncing from a reflector back to the LED??? I'm assuming i'm reading this wrong, but i can see the idea being reasonable.


No, the dome is prevent light from being bounced around inside the LED die itself (hence the term internal reflection). Remove the dome and you usually see the output decrease by something like 20 to 25%. This light is no longer making it out of the LED die.


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## jso902 (May 5, 2014)

jtr1962 said:


> No, the dome is prevent light from being bounced around inside the LED die itself (hence the term internal reflection). Remove the dome and you usually see the output decrease by something like 20 to 25%. This light is no longer making it out of the LED die.



How is that different from what I said? 
an analogy of this would be a fixture in my room will emit light and will exit through the window section and this would prevent light from re-entering back into the room. 
But if the light already emits towards the base/circuit board, no dome would prevent that unless it completely encompasses the unit or unless there's a reflective backing that bounces the light forward. 

Mind you this comment is on macro objects. And I do understand that atoms/electrons/light or photon may act differently.


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## jtr1962 (May 5, 2014)

jso902 said:


> How is that different from what I said?
> an analogy of this would be a fixture in my room will emit light and will exit through the window section and this would prevent light from re-entering back into the room.
> But if the light already emits towards the base/circuit board, no dome would prevent that unless it completely encompasses the unit or unless there's a reflective backing that bounces the light forward.
> 
> Mind you this comment is on macro objects. And I do understand that atoms/electrons/light or photon may act differently.


You mentioned light bouncing from a reflector back to the LED. First off, not every light uses a reflector. In fact, they're not needed in many types of general area lighting. Second, even when there is a reflector a very small fraction of the light from the reflector makes it back to the dome. The purpose of the reflector is to focus light coming from the LED. As such, it's designed so that most of the light which reaches it from the LED ends up going forwards, not back towards the LED. The dome and silicone filling exists for one purpose only-to make sure more light gets of the LED die, not to prevent any light which is reflected back to the LED from reentering the LED die. In other words, the dome/filling has absolutely nothing to do with anything which is happening on a macro scale.

Here is a good explanation of the entire concept.

Incidentally, extraction efficiency is important to further improving the efficiency of LEDs. Even 10 years ago LEDs typically converted most of their input power to photons. The problem is most of these photons never made it out of the die. Thanks to more closely matching the refractive indices of the die and encapsulant, nowadays extraction efficiency is well above 50%.


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## jso902 (May 5, 2014)

TEEJ said:


> LED do not really make much UV, and, it gets EXPENSIVE for example to make LED that emit strongly in the UV spectrum, say lower than ~ 390 nm....albeit the violet and purple end of things is super well endowed (So if we call 390 nm and shorter "UV", the LED itself is emitting mostly above that in "Near UV" territory, up to "blue" depending on the LED type... The phosphors are to make it less "Angry Purple", as they take that light, and emit more of the rest of the visible spectrum.
> 
> Now, since our eyes REALLY DO see other parts of the spectrum better, we can't see as well when forced to use the other parts of the spectrum, so, we DO need more of that frequency band to actually resolve equivalent details.



Clear as mud  hahaha. Still working on grasping all of this. I also updated the first post so people don't have to sift through everything. Hopefully it's correct. If it's wrong, please let me know. 

I'm entering into an area that might get some hash, but I'll cross my fingers...
My understanding of the light spectrum/color is that our eyes are not more sensitive to red then blue because we can't see them. I thought the problem was that blue colors have such a high frequency/short wavelength that it tends to scatter off its energy. And as a result, the intensity drops off quickly. Hence the reason why it's easier for us to see a low intensity red as opposed to blue.


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## Harold_B (May 5, 2014)

Seems the topic of the dome and what it does never gets put to rest (on CPF anyway) but here's another older thread that makes the case for out coupling a little more clear. Or maybe not. 

http://www.candlepowerforums.com/vb/showthread.php?368421-Why-does-de-doming-cause-a-warm-tint-shift


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## TEEJ (May 6, 2014)

jso902 said:


> Clear as mud  hahaha. Still working on grasping all of this. I also updated the first post so people don't have to sift through everything. Hopefully it's correct. If it's wrong, please let me know.
> 
> I'm entering into an area that might get some hash, but I'll cross my fingers...
> My understanding of the light spectrum/color is that our eyes are not more sensitive to red then blue because we can't see them. I thought the problem was that blue colors have such a high frequency/short wavelength that it tends to scatter off its energy. And as a result, the intensity drops off quickly. Hence the reason why it's easier for us to see a low intensity red as opposed to blue.



Its MORE because we evolved to be able to perceive a narrow band of the spectrum, and, the chemicals in our eyes that allow us to interpret that band are optimized for that greenish/yellow part of the spectrum...and the CHEMICALS we are forced to perceive with simply work better in that wavelength, and less well in the reds, etc.

Some people do have better abilities, or worse abilities than others do in that regard, but, generally, we all see better in that part of the spectrum due to the chemistry of our photoreceptors more than due to the scattering, etc. We're only talking about a few nanometers of wavelength here, its a narrow slice.



Species with better photoreceptor chemistry (A Mantis Shrimp for example), see those colors just fine, with not a care in the word about light scattering, etc. They can see great in Deep UV, Far IR, everything in between, etc...incredible dynamic range.

So, sure, there is scattering, but, its not the problem...its the photoreceptors we're stuck with.



In the OP, the first section is a bit off...the heat is not from the off spectrum emissions, its from the electronics behind the LED. The LED is not emitting IR/Heat as a result of the phosphors, its a result of the heat from the electronics that supply power to the LED.

The BEAM of the LED is not the hot part....THAT'S an incandescent bulb issue, not an LED issue.



Incan bulbs make mostly heat, with a little teeny amount of light, percentage-wise. The BEAM is mostly heat.

LED make mostly LIGHT, and the heat is not from the output, its from the process running the LED, behind it. The BEAM is light.


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## jso902 (May 8, 2014)

jtr1962 said:


> You mentioned light bouncing from a reflector back to the LED. First off, not every light uses a reflector. In fact, they're not needed in many types of general area lighting. Second, even when there is a reflector a very small fraction of the light from the reflector makes it back to the dome. The purpose of the reflector is to focus light coming from the LED. As such, it's designed so that most of the light which reaches it from the LED ends up going forwards, not back towards the LED. The dome and silicone filling exists for one purpose only-to make sure more light gets of the LED die, not to prevent any light which is reflected back to the LED from reentering the LED die. In other words, the dome/filling has absolutely nothing to do with anything which is happening on a macro scale.
> 
> Here is a good explanation of the entire concept.
> 
> Incidentally, extraction efficiency is important to further improving the efficiency of LEDs. Even 10 years ago LEDs typically converted most of their input power to photons. The problem is most of these photons never made it out of the die. Thanks to more closely matching the refractive indices of the die and encapsulant, nowadays extraction efficiency is well above 50%.



This stuff requires a lot of coffee and sloooooow reading...

If read correctly, 
an LED is a cube with a phosphor layer on top of it. Light must pass through layer(s) before coming out as light. And in the process, there is reflection by the layer which transmits the light back down to the surface/parallel(i.e. any direction but forward). 
This is considered TIR (total internal reflection; not the TIR lens). This effect leads to either wasted light or heat.

And future LED's development will be dependent on whether the LED shape or phosphor coating is modified in such a way that light only moves perpendicular to the surface; thus reducing lost energy due to reflection.

question: 
1. why do they say the efficiency is 13% when wikipedia says light efficiency is closer to 70-90% dependent on the color? sounds like i'm not comparing apples to apples.

2. the photo of the XML2 has 3 leads inside of it; Why is it 3 and not 2?


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## jtr1962 (May 8, 2014)

jso902 said:


> 1. why do they say the efficiency is 13% when wikipedia says light efficiency is closer to 70-90% dependent on the color? sounds like i'm not comparing apples to apples.


13% is the maximum theoretical extraction efficiency of a cube in air. By shaping the die, and surrounding it with materials other than air, we have greatly exceeded 13% extraction efficiency.

I'm not sure which wikipedia article you're referring to which states LED efficiency is 70% to 90%. Some blue LEDs in the lab may have hit 90+% but the highest commercial efficiency I'm aware of is ~60% for blues. Reds and greens are around 25% at most. Deep reds are up to about 50%.



> 2. the photo of the XML2 has 3 leads inside of it; Why is it 3 and not 2?


They use more leads to distribute the current more uniformly in the die. This avoids the current concentrating in one part of the die and creating hot spots which would be a source of inefficiency.


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## jso902 (May 8, 2014)

ColorWavelength range (nm)Typical efficacy (lm/W)Typical efficiency (W/W)Red620 < _λ_ < 645720.39Red-orange610 < _λ_ < 620980.29Green520 < _λ_ < 550930.15Cyan490 < _λ_ < 520750.26Blue460 < _λ_ < 490370.35
http://en.wikipedia.org/wiki/Light-emitting_diode#Efficiency_and_operational_parameters

****THE TABLE IS OFF ON THE FIRST ROW****
If that's true, then i'm reading the wrong area for efficiency. I should be looking at the last column W/W efficiency not lumen/watt; correct?


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## jtr1962 (May 8, 2014)

jso902 said:


> ColorWavelength range (nm)Typical efficacy (lm/W)Typical efficiency (W/W)Red620 < _λ_ < 645720.39Red-orange610 < _λ_ < 620980.29Green520 < _λ_ < 550930.15Cyan490 < _λ_ < 520750.26Blue460 < _λ_ < 490370.35
> http://en.wikipedia.org/wiki/Light-emitting_diode#Efficiency_and_operational_parameters
> 
> ****THE TABLE IS OFF ON THE FIRST ROW****
> If that's true, then i'm reading the wrong area for efficiency. I should be looking at the last column W/W efficiency not lumen/watt; correct?


Yes, the last column is what you would be interested in, and the numbers they have seem to be right, although blue is past 0.60 (60%) these days.


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## jso902 (May 9, 2014)

jtr1962 said:


> 13% is the maximum theoretical extraction efficiency of a cube in air. By shaping the die, and surrounding it with materials other than air, we have greatly exceeded 13% extraction efficiency.
> 
> I'm not sure which wikipedia article you're referring to which states LED efficiency is 70% to 90%. Some blue LEDs in the lab may have hit 90+% but the highest commercial efficiency I'm aware of is ~60% for blues. Reds and greens are around 25% at most. Deep reds are up to about 50%.
> 
> ...



Where does 13% come from? 
And what's the purpose of Lm/Watt? is it to gauge / compare various light sources to each other?
btw, jtr, thank you very much for answering a lot of my questions. everytime I answer one question, I feel like there's 15 more that pop up :hairpull:


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## jtr1962 (May 9, 2014)

jso902 said:


> Where does 13% come from?


Math and theoretical physics.



> And what's the purpose of Lm/Watt? is it to gauge / compare various light sources to each other?
> btw, jtr, thank you very much for answering a lot of my questions. everytime I answer one question, I feel like there's 15 more that pop up :hairpull:


Lumens per watt shows how much visible light the source puts out for every watt it consumes. As you might know, the human eye is more sensitive to some wavelengths than others. Lumens take this into account while radiant efficiency doesn't. That's why a green source with an electrical efficiency of only 15% puts out more lumens per watt than a blue source with an efficiency of 35%. The eye is much more sensitive to green light than to blue light.


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## Marcturus (Jun 30, 2014)

Great place to throw in another number: 14%
(using 650nm, narrow-red emitting phosphor, association with Lumileds; research effort about this sort of thing was mentioned by SemiMan)
http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4012.html


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## bshanahan14rulz (Jun 30, 2014)

Oh, my! Quite a jump by just swapping out an ingredient in the recipe.


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## TEEJ (Jul 1, 2014)

I was reading that a new technology was developed that mimics the scale formation in fireflies, and, using the scales, a 50% increase in lumen output was attainable. Its not in production yet though.


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## bshanahan14rulz (Jul 1, 2014)

That specific layered scale tech may not be in production, but that trick has been used for a while now. It seems that the surfaces of these chips are always very rough, ragged, never smooth. I imagine this is an easy-to-create texture, compared to the intricate scales of a firefly. Some chips have a more macro-sized feature, the funky pyramid seen on some Cree chips. 

Do the scales act as a way to smooth out the change in refractive index, like a grin lens, I guess? This is the time of year fireflies are on my mind. And in the house, and on the windscreen, and in the yard...


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