# Phosphor conversion of photons in LEDs & photon recycling efficiency



## Genzod (Feb 23, 2018)

I know that phosphor in an LED converts some of the blue photons supplied to it into yellow photons to create white light. 

I'm wondering what happens when other colors of photons are supplied to the phosphor. What would happen if green photons enter the phosphor layer? Yellow photons?

Thanks.

Edit: Also interested in understanding photon recycling efficiency that increases LED luminance. How are the losses in a waiven collar accounted for when photons are sent back to the die for recycling? In the set up below (credit: [email protected] Taschenlampen Forums), the gain is 2.2x over the fraction of light defined by the flux ratio of solid angles for a 30 degree half angle beam opening--a 55% efficiency of a potential of 4x. The reflector is 99% efficient but it seems to pass quite a bit of light despite the rating.


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## brickbat (Feb 25, 2018)

*Re: Phosphor conversion of photons in LEDs*

Generally a phosphor provides photons at a wavelength (color) related to its molecular and crystalline structure, and not related to the wavelength of the incoming light. If the wavelength of the incoming light becomes too long, the phosphor won't emit any light.


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## archimedes (Feb 25, 2018)

*Re: Phosphor conversion of photons in LEDs*

There are differences between blue and violet pumped emitters, for example ...

http://www.candlepowerforums.com/vb...olet-pump-based-ultra-high-cri-mid-power-leds


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## Genzod (Feb 25, 2018)

*Re: Phosphor conversion of photons in LEDs*



brickbat said:


> Generally a phosphor provides photons at a wavelength (color) related to its molecular and crystalline structure, and not related to the wavelength of the incoming light. If the wavelength of the incoming light becomes too long, the phosphor won't emit any light.



So if you have a typical blue emitter with yellow phosphor, the phosphor crystalline structure is designed to create yellow photons. But if the wavelength of the emitter increases, the generation of yellow photons will decrease until a point is reached where no more yellow photons will be generated, is that correct?

If so, is that because the energy difference between the emitter source photons and the phosphor photons is approaching zero? Hence a hypothetical red or orange emitter can't give rise to yellow photons in that yellow phosphor?


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## Genzod (Feb 25, 2018)

*Re: Phosphor conversion of photons in LEDs*



archimedes said:


> There are differences between blue and violet pumped emitters, for example ...
> 
> http://www.candlepowerforums.com/vb...olet-pump-based-ultra-high-cri-mid-power-leds



Indeed. When Violet Beauregarde ate the yellow phosphor gum, the _violet pumping_ was so markedly increased, she had to be rolled away and juiced.


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## The_Driver (Feb 26, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> So if you have a typical blue emitter with yellow phosphor, the phosphor crystalline structure is designed to create yellow photons. But if the wavelength of the emitter increases, the generation of yellow photons will decrease until a point is reached where no more yellow photons will be generated, is that correct?
> 
> If so, is that because the energy difference between the emitter source photons and the phosphor photons is approaching zero? Hence a hypothetical red or orange emitter can't give rise to yellow photons in that yellow phosphor?



Normal white LEDs use YAG:Ce phosphor. Here you can see the absorption spectrum of this type of phosphor. It should answer your question.
This absorption and emission phenomenon is called Stokes Shift.

Here you can find a nice article on the topic.


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## ssanasisredna (Feb 26, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> So if you have a typical blue emitter with yellow phosphor, the phosphor crystalline structure is designed to create yellow photons. But if the wavelength of the emitter increases, the generation of yellow photons will decrease until a point is reached where no more yellow photons will be generated, is that correct?
> 
> If so, is that because the energy difference between the emitter source photons and the phosphor photons is approaching zero? Hence a hypothetical red or orange emitter can't give rise to yellow photons in that yellow phosphor?



That is correct, and unfortunately at least at this point in time, only one photo out for each photon in, and as the emitted photons are less energetic, there is an efficiency loss equal to the ratios of the wavelengths.


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## Genzod (Feb 26, 2018)

*Re: Phosphor conversion of photons in LEDs*



ssanasisredna said:


> That is correct, and unfortunately at least at this point in time, only one photo out for each photon in, and as the emitted photons are less energetic, there is an efficiency loss equal to the ratios of the wavelengths.





The Driver said:


> Normal white LEDs use YAG:Ce phosphor. Here you can see the absorption spectrum of this type of phosphor. It should answer your question.
> This absorption and emission phemnomenon is called Stokes Shift.
> 
> Here you can find a nice article on the topic.



Thanks everyone.

Up until now, I wasn't sure where the extra energy was going from the shift. I thought perhaps _part_ of the increased surface brightness of an LED undergoing the photon recycling that arises from a *wavien collar* was coming from the ratio of wavelengths. But now it would appear redirection of the formerly wasted wall light undergoes about a 15% loss from reflection and a tint shift toward yellow of any higher energy photons that make it back into the phosphor, representing a further energy loss due to conversion. The gain in surface brightness in LED due _only***_to the super-positioning of redirected photons that eventually escape through the collar's hole toward the lens. 

***Unless I'm overlooking something else, of course.  Any comments regarding that?


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## brickbat (Feb 26, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> ...I wasn't sure where the extra energy was going from the shift....



High energy photon enters a phosphor, low energy photon exits. The energy difference shows up as heat in the phosphor, no?


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## Genzod (Feb 26, 2018)

*Re: Phosphor conversion of photons in LEDs*



brickbat said:


> High energy photon enters a phosphor, low energy photon exits. The energy difference shows up as heat in the phosphor, no?



Exactly. In my mind, I had imagined two boundaries describing the energy balance:

1) For every 100 blue photons phosphor generates 120 yellow photons (assuming wavelength ratio 1:1.2)

2) For every 100 blue photons phosphor generates 100 yellow photons and the extra energy from the wavelength ratio represents an efficiency loss, e.g. heat.

(or something in between) 

Answer confirmed above by *ssanasisredna* as item 2.


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## The_Driver (Feb 27, 2018)

*Re: Phosphor conversion of photons in LEDs*

The Wavien Collar redirects the light onto the phosphor. The blue part is "recycled". It can come back out at a different angle (converted light is scattered isotropically in phosphor) and is converted to yellow-green. 75% of the emitted light (of a domeless LED) is collected by the collar and the remaining 25% is amplified by a max of 120%. Thus the efficiency in terms of lumens is 55%. 
See here for more details (in German).


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## Genzod (Feb 27, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> The Wavien Collar redirects the light onto the phosphor. The blue part is "recycled". It can come back out at a different angle (converted light is scattered isotropically in phosphor) and is converted to yellow-green. 75% of the emitted light (of a domeless LED) is collected by the collar and the remaining 25% is amplified by a max of 120%. Thus the efficiency in terms of lumens is 55%.
> See here for more details (in German).



That's a very decent article. _Vielen Dank!_

I had likewise introduced the Lambert cosine through each dA area element in the hemisphere and integrated to get the same sin2​θ result, so it was reassuring I was working with the correct formula.

With 99% reflectivity, I would think the gain to have been close to 4X, not 2.2x, so I can see where you get the 55% efficiency. Is that inefficiency due the low critical angle of the phosphor and air, resulting in reflections that repeatedly bounce themselves off the phosphor and back to the reflector ad infinitum to eventual absorption? 

If so, would it help greatly to have a roughened phosphor to improve chances of reentering the phosphor so they can reemerge at a steeper angle and have a better chance of exiting the hole? I think that's the case with the newer XPG2 and XPG3 phosphors. I'm wondering if gain has been improved using a collar with those LEDs?


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## The_Driver (Feb 27, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> With 99% reflectivity, I would think the gain to have been close to 4X, not 2.2x, so I can see where you get the 55% efficiency. Is that inefficiency due the low critical angle of the phosphor and air, resulting in reflections that repeatedly bounce themselves off the phosphor and back to the reflector ad infinitum to eventual absorption?



I don't know the answer to that.
Possible reasons:
- Phosphor saturated by the heat of the die underneath and the additional heat from the light reflected by the collar
- the die underneath the phosphor could be overheating from the reflected light causing it to emit less blue light which in turn reduced total amount of available light
- reflection as you mentioned (what I know: at 90° angle the phosphor reflects ~3% at the phosphor-air-junction)




Genzod said:


> If so, would it help greatly to have a roughened phosphor to improve chances of reentering the phosphor so they can reemerge at a steeper angle and have a better chance of exiting the hole? I think that's the case with the newer XPG2 and XPG3 phosphors. I'm wondering if gain has been improved using a collar with those LEDs?



sma tested the collars with a de-domed XP-G2 (this LED had the highest known luminance of all LEDs in the beginning of 2015). The phosphor of the XP-G2 is pretty rough. The newer XP-G3 on the other hand has a much lower luminance because the effective die size is much larger. Its die is basically 3D, it also emits light to the sides. Generally it can be said that the XP-G3 is a fundamentally different LED compared to the XP-G2.


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## Genzod (Feb 27, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> I don't know the answer to that.
> Possible reasons:
> - Phosphor saturated by the heat of the die underneath and the additional heat from the light reflected by the collar
> - the die underneath the phosphor could be overheating from the reflected light causing it to emit less blue light which in turn reduced total amount of available light
> - reflection as you mentioned (what I know: at 90° angle the phosphor reflects ~3% at the phosphor-air-junction)...



Okay, great to understand other avenues of potential losses. At least heat can be managed.

I'm a little confused about your last mention. The critical angle (from the vertical) for air and phosphor is about 34 degrees, right? So wouldn't very shallow angles of approach (coming from 90 degrees from vertical) mostly bounce right off the phosphor, like that reflected at the base of the reflector (90 degrees)? It seems like you're saying 97% of photons approaching LED from the bottom of the reflector is absorbed (3% reflected). I'm thinking 3% absorption and 97% reflection at that horizontal vector. Maybe our angle conventions are opposite, or I'm just not familiar enough with the physics here.


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## The_Driver (Feb 27, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> Okay, great to understand other avenues of potential losses. At least heat can be managed.
> 
> I'm a little confused about your last mention. The critical angle (from the vertical) for air and phosphor is about 34 degrees, right? So wouldn't very shallow angles of approach (coming from 90 degrees from vertical) mostly bounce right off the phosphor, like that reflected at the base of the reflector (90 degrees)? It seems like you're saying 97% of photons approaching LED from the bottom of the reflector is absorbed (3% reflected). I'm thinking 3% absorption and 97% reflection at that horizontal vector. Maybe our angle conventions are opposite, or I'm just not familiar enough with the physics here.



I meant that when you shine blue light from straight-on (vertical) toward a flat piece of phosphor, 3% of the light is reflected back at the phosphor-air junction. Very shallow angles probably increase this percentage for a flat piece of phosphor. 

Here's a picture of a nicely de-domed Cree LED. Around it you can see the reflective LED package. The exposed phosphor-silicon-mix reflects much less light than the package, it has a much rougher surface. All flashlights with Wavien collar that achieved very high luminance values used de-domed XP-G2 LEDs or now Osram Black Flat LEDs (no dome from the factory, but much smoother surface compared to de-domed Cree LEDs). 

Here you can find some more detailed findings regarding the optical properties of the phosphor-silicone-mix used in LEDs.


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## Genzod (Feb 27, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> I meant that when you shine blue light from straight-on (vertical) toward a flat piece of phosphor, 3% of the light is reflected back at the phosphor-air junction. Very shallow angles probably increase this percentage for a flat piece of phosphor.



Okay, haha! Our angle conventions were different and opposite. You were describing a downward perpendicular approach, hence 90 degrees from base, and I was thinking 90 degrees measured from the vertical axis--photons moving horizontally.



> Here's a picture of a nicely de-domed Cree LED. Around it you can see the reflective LED package. The exposed phosphor-silicon-mix reflects much less light than the package, it has a much rougher surface. All flashlights with Wavien collar that achieved very high luminance values used de-domed XP-G2 LEDs or now Osram Black Flat LEDs (no dome from the factory, but much smoother surface compared to de-domed Cree LEDs).
> 
> Here you can find some more detailed findings regarding the optical properties of the phosphor-silicone-mix used in LEDs.



I'll definitely read that publication, thanks!


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## Genzod (Feb 27, 2018)

*Re: Phosphor conversion of photons in LEDs*

I was looking over this reference *TheDriver* supplied. In the post, SMA is describing his experiment where he determines the luminance gain arising from a large wavien collar centered on a dedomed XP-G2. I'll describe what I think is going on here with this configuration, and I hope someone of experience would jump in to guide and correct my thinking.

It's hard to say exactly whether the XP-G2 *SMA*@Taschenlampen Forums pulled out of his scrap box was bare phosphor, had a sealant over the bare phosphor or if the dedome was a slice job with some silicone remaining over the bare LED. If someone here knows *SMA*, that information would be helpful in my understanding of photon recycling. This fact is critical to understanding the behavior of reflected photons returning to the emitter surface.

Assuming the XP-G2 has a seal and the sealing material has a refractive index of 1.5 like silicone, the critical angle between air and silicone would be about 42 degrees. (measured from the vertical axis ) If the seal is perfectly smooth (assume for the moment), I would expect all photons approaching the phosphor at 42 degrees or more would simply bounce off the barrier and head to the opposite side of the collar for another 99% reflection and 1% absorption. It would take a number of reflections back and forth like a PONG game to be completely absorbed by the mirror.

Photons approaching at less than 42 degrees from vertical axis (regardless of wavelength) would enter the seal, then the phosphor, and some with enough energy (shorter wavelength) would be converted to lower energy photons. Those surviving, converted and unconverted photons would take another stab at a favorable exit angle that allows escaping the dome or get stuck in a reflective loop until completely absorbed by the mirror.

In essence, only the region of the mirror from 30-42 degrees supports increasing the luminance of the LED. The region from 42-90 degrees would eventually be absorbed by the mirror.

Of course this is not a perfect world with perfect surfaces, so I would expect the line to be less tightly defined (blurred/transitioned). Roughness of the LED surface would change angles of incidence to favor more re-absorption and emission, so I would anticipate the useful area of the mirror might extend beyond 42 degrees a bit.

If I use the following formula:

*GAIN = K* sin2​γ / sin2​**θ* 

(Ratio of flux through solid angles times a correction factor: constant * [critical angle of the die's top layer / half angle of the collar port].)

Where γ=42 degrees (gamma) is the critical angle of the first layer of the LED and θ=30 degrees (theta) is the half-angle of the collar's port (both measured from the vertical axis), and GAIN is about 2.20 in the posted experiment from Taschenlampen Forums, K becomes 1.23. If I set K to 1 and predict the angle that divides the useful from non-useful regions of the mirror, I get 48 degrees, which is close to the critical angle, deviated only by 6 degrees. I would therefore suspect surface roughness is responsible for the 6 degree offset in prediction of that line.

If the phosphor were bare, I would expect the critical angle to be around 34 degrees from vertical. The phosphor surface would probably be rougher than a sealed surface so I would expect the line to be lower than 40 degrees but probably not beyond 48 degrees.

This is all just conjecture from a photon noob, and I'm not trying to assert that that is what is actually going on here. But at the moment, it is what I'm thinking is happening as I'm trying to understand this physics. 

Anyone here with some expertise that can give some knowledgeable insight, guidance or correction? Thanks.*

EDIT: **Conceptual error: *I re-examined my calculations for photons approaching the die at shallow angles. 

Snells law can't describe an angle of approach that prevents photons from entering a slower medium (air to phosphor) like it can in reverse (phosphor to air) to describe TIR. 

If photons in air coming from 70 degrees (from vertical axis) impact the phosphor surface, refraction into the die takes place 31 degrees from the vertical axis. Even 90 degrees has a refractive angle of 34 degrees from normal, as weird as that seems to my intuition (due to particle wave duality). So refraction is always taking place from all angles of approach coming from the collar to the die. 
​


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## JoakimFlorence (Feb 28, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> I'm wondering what happens when other colors of photons are supplied to the phosphor. What would happen if green photons enter the phosphor layer? Yellow photons?


Above about 500nm (green-cyan) YAG phosphor has a very low level of absorption.

Not directly relevant to your question but a while back I was doing some research into blue-green (cyan) phosphors, and with the types of phosphors used in LEDs (including the advanced new ones that have just been developed) it generally takes an excitation source at least 40 nanometers less than the peak emission you hope to get from the phosphor. Try to excite the phosphor with a wavelength that's just barely less than the normal peak wavelength emission of the phosphor and it will end up shifting the wavelength distribution towards longer wavelengths, so that there will still be that characteristic gap in the spectrum. Although the minimum of the gap might be as high as 45 percent of the peak phosphor value.


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## Agpp (Feb 28, 2018)

*Re: Phosphor conversion of photons in LEDs*

As to losses: Light converted by phosphor and emitted at wrong angle will not be reflected back and therefore will be lost.


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## The_Driver (Feb 28, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> I was looking over this reference *TheDriver* supplied. It's hard to say exactly whether the XP-G2 *SMA*@Taschenlampen Forums pulled out of his scrap box was bare phosphor, had a sealant over the bare phosphor or if the dedome was a slice job with some silicone remaining over the bare LED. If someone here knows *SMA*, that information would be helpful in my understanding of photon recycling.
> 
> In the post, SMA is describing his experiment where he determines the luminance gain arising from a large wavien collar centered on a dedomed XP-G2. I'll describe what I think is going on here with this configuration, and I hope someone of experience would jump in to guide and correct my thinking.



I know him personally. He used a cool-white XP-G2 and de-domed it using the classic way (imersion in nitro paint thinner or similar). This removes the silicone lens on top of the LED, but does not (to my knowledge) alter the silicon-phosphor-mix underneath. But you can ask him yourself, he is also a member here on the forum.


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## Genzod (Mar 1, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> I know him personally. He used a cool-white XP-G2 and de-domed it using the classic way (imersion in nitro paint thinner or similar). This removes the silicone lens on top of the LED, but does not (to my knowledge) alter the silicon-phosphor-mix underneath. But you can ask him yourself, he is also a member here on the forum.



Thanks, Driver. I got a reply from him today. He used a chemical dedome with no sealer. That means the index of refraction is 1.0 and 1.8 and the critical angle is 34 degrees. Since the difference between the virtual critical angle of 48 (that yields 55% efficiency in lumen gain) and the actual critical angle is 14 degrees, I think it implies the exposed phosphor is rough, changing incident angles of photon impacts and facilitating better absorption to capture more of the reflected light.


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## Genzod (Mar 1, 2018)

*Re: Phosphor conversion of photons in LEDs*

*Conceptual error*: I re-examined my calculations for photons approaching the die at shallow angles. 

Snells law can't describe an angle of approach that prevents photons from entering a slower medium (air to phosphor) like it can in reverse (phosphor to air) to describe TIR. 

If photons in air coming from 70 degrees (from vertical axis) impact the phosphor surface, refraction into the die takes place 31 degrees from the vertical axis. Even 90 degrees (horizontal to die surface) has a refractive angle of 34 degrees from normal, as weird as that seems to my intuition. So there is always some refraction taking place from all angles of approach coming from the collar to the die. 

What I need to understand now is: to what extent photons are _also_ reflecting off the phosphor at shallow angles of approach. I've seen a *% reflection vs. angle of incidence* profile for air to glass. Does anyone know where i might find such a profile for air to bare YAG phosphor?


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## Genzod (Mar 2, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> - reflection as you mentioned (what I know: at 90° angle the phosphor reflects ~3% at the phosphor-air-junction)



Now that I have a better grip on reflection/refraction with Snell's law (considering photons as a particle only without equal attention to its dual wave nature had thrown me for a conceptual loop), I reconsidered what you said here and it makes a lot more sense now, and is very helpful. 

I found this equation for normal reflectance from this source:







I don't know if this form of equation can be applied generally to the indices of different mediums. Pressing carelessly ahead, using 1.8 for phosphor and 1 for air and substituting, I get 8% reflection for head on air to phosphor. Do you have a reference for the 3% you mentioned?

For glass, head on, reflection is about 4% with 96% transmittance. When the incident angle approaches about 60 degrees, the efficiency improves (I think close to 0% reflection), then starts dropping again toward 4% reflection as angle continues to become more shallow (as when the aspheric lens is twisted closer to the LED for flood). Here is the profile of reflectance vs. incident angle for glass with more detail beyond 70 degrees in the original plot of this I saw elsewhere. There might be some analogy here with air and phosphor. If I could just find a similar plotted profile for the optical efficiency of phosphor.

To throw another wrench into my noobular mindset, I'm wondering if bare air to phosphor reflections of light rays returning from the reflector are Lambertian (2nd type) and possibly dominated by yellow green wavelengths?


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## The_Driver (Mar 2, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> I don't know if this form of equation can be applied generally to the indices of different mediums. Pressing carelessly ahead, using 1.8 for phosphor and 1 for air and substituting, I get 8% reflection for head on air to phosphor. Do you have a reference for the 3% you mentioned?



Yes, here. It's basically just the fresnel equations. 

You need to take into acount that no LED hast just phosphor. It's always a phosphor silicone mix which mostly contains silicone. Thus you need to use the refractive index of silicone for 450nm: ~1.41
If you want to be really precise you need to take into account the temperature related shift of the refractive index of silicone and also the temperature related shift of the dominant wavelength of the blue led die.


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## Genzod (Mar 2, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> Yes, here. It's basically just the fresnel equations.
> 
> You need to take into account that no LED has just phosphor. It's always a phosphor silicone mix which mostly contains silicone. Thus you need to use the refractive index of silicone for 450nm: 1,41



Okay, I just used the refraction index of 1.8 for a phosphor type LED from Dr. Jones CPF/BLF. I see using 1.41 for silicone you get about 3%.

I also see in the article reference you provided that the reflection for a phosphor LED type surface is specular not Lambertian. Thank you.


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## The_Driver (Mar 2, 2018)

*Re: Phosphor conversion of photons in LEDs*

I researched this stuff during the past year for my laser phosphor project. I summarized my findings including the sources here (all in German).


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## Genzod (Mar 2, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> I researched this stuff during the past year for my laser phosphor project. I summarized my findings including the sources here (all in German).



What an amazing study!_ Ausgezeichnet! _I had read an article from Dec 2017 where a university was studying laser based LEDs. They said the anticipated results would improve efficacy by 10x over the typical YAG phosphor LED. I was contemplating getting a blue laser and targeting a cooled LED to see how it might improve upon the wavien collar, and you saved me a little work! I was discussing this with *Degarb*. I think if they are able to provide LEDs with 10x luminance over what we have now in the XPG2, the wavien collar will die an untimely death. Even if laser LEDs cost 10x that of a $3 XPG2, that's still 3-4x less than a wavien collar that only gets you 2.2x.


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## The_Driver (Mar 3, 2018)

*Re: Phosphor conversion of photons in LEDs*

The LED with the highest luminance (Osram Black Flat HWQP) currently does up to 260cd/mm^2. Osram already offers a laser phosphor module with 3700cd/mm^2. That is in the realm of the best short-arc bulbs (up to 6000cd/mm^2). This module is much bigger though than a XP-G2 based flashlight.

At the present time laser phosphor modules are much more expensive compared to LEDs. If you want 1000 lumens (to get a somewhat large hotspot) you will need to pay at least 100-150$. You need the expensive diode, the phosphor target and a special laser driver (more precisely regulated). You also need to think about safety if you are using separate components.

A nice alternative might be the Soraa SLD. It's a smd module with laser and phosphor that doesn't emit any laser radiation.

The Wavien collar is already "dead". The company is gone. Another company owns the patent, but is not selling it separately and not fully using its potential in the one light they offer.


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## Genzod (Mar 3, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> The LED with the highest luminance (Osram Black Flat HWQP) currently does up to 260cd/mm^2. Osram already offers a laser phosphor module with 3700cd/mm^2. That is in the realm of the best short-arc bulbs (up to 6000cd/mm^2). This module is much bigger though than a XP-G2 based flashlight.



The Wavien collar takes up a bit of space itself, and then you have to create more available length in the light cavity to meet a 60 degree beam that ordinarily would be 90-120 degrees. With the wavien collar in the way, the ability to zoom to flood is lost to a great degree. I haven't seen any laser modules as of yet, but I would imagine that the option of constructing the laser to come from under the phosphor would leave the space in front free of obstruction.

I'm glad to hear Osram is offering an LD module! Could you link me to a sales page for the one you mentioned? *EDIT*: Okay, called Phaser 3000 and Phaser 500. Got it.

*EDIT:* With 3700 cd/mm^2 @40 watts, I get about 2730 cd/mm^2 @18.63w for a maxed out Flat Black for the comparison. If the 260 luminance figure you provided is anywhere close to 795 lm @ 4.6A and 4.05V, then that's roughly 10x more intensity for the same power supplied.

Size and weight for the product is 90mmx220mmx175mm and 3.9kg, not exactly EDC yet.



> At the present time laser phosphor modules are much more expensive compared to LEDs. If you want 1000 lumens (to get a somewhat large hotspot) you will need to pay at least 100-150$. You need the expensive diode, the phosphor Target and a special laser driver (more precisely regulated). You also need to think about safety if you are using separate components.



So it is nearly breaking even with the old price of the collar, and it is certainly cheaper than having one made for you by a machine shop or a molding and coating manufacturer. At least now you can buy a module, which is something you can't do with the present Waiven patent owners.



> The Wavien collar is already "dead". The company is gone. Another company own the patent, but not selling it separately and not fully using its potential in the one light they offer.



As long as the patent is still out there and has legal bite, the collar technology has value and the idea is still alive even though the manufacturing company is dead. I meant that the legal threat of the patent will become irrelevant when the technology loses its relevance in lieu of the laser module revolution. I would expect prices for laser modules to eventually come down just like anything else. I remember when it cost several thousands of dollars for a 40" 1080p LED TV. We waited for the technology to become cheap and bought ours for $500.


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## The_Driver (Mar 4, 2018)

*Re: Phosphor conversion of photons in LEDs*




Genzod said:


> The Wavien collar takes up a bit of space itself, and then you have to create more available length in the light cavity to meet a 60 degree beam that ordinarily would be 90-120 degrees. With the wavien collar in the way, the ability to zoom to flood is lost to a great degree. I haven't seen any laser modules as of yet, but I would imagine that the option of constructing the laser to come from under the phosphor would leave the space in front free of obstruction.





Genzod said:


> I'm glad to hear Osram is offering an LD module! Could you link me to a sales page for the one you mentioned? *EDIT*: Okay, called Phaser 3000 and Phaser 500. Got it.
> 
> *EDIT:* With 3700 cd/mm^2 @40 watts, I get about 2730 cd/mm^2 @18.63w for a maxed out Flat Black for the comparison. If the 260 luminance figure you provided is anywhere close to 795 lm @ 4.6A and 4.05V, then that's roughly 10x more intensity for the same power supplied.
> 
> ...



Yes, the collar is not really a very practical thing. It was also overly expensive considering what it does. They could have made it out of aluminium and offered it for a quarter of the price. 

The lasers are already cheap if you are ok with a using multiple diodes in a single light (a laser bank where all the beams are combined using optics). Only the very powerful multi-watt diodes from Osram and Nichia are actually expensive.

The Osram Black Flat's luminance has been measured by multiple people and several record braking throwers have been built with it. The highest value ever measured (that I have seen) is 260cd/mm^2 at maximum output (4.5-5A). In the light linked in my sig we got up to around 240-250cd/mm^2.

*EDIT:* your PM box is full!


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## Genzod (Mar 4, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> Yes, the collar is not really a very practical thing. It was also overly expensive considering what it does. They could have made it out of aluminium and offered it for a quarter of the price.
> 
> The lasers are already cheap if you are ok with a using multiple diodes in a single light (a laser bank where all the beams are combined using optics). Only the very powerful muliti-watt diodes from Osram and Nichia are actually expensive.
> 
> ...



Entschuldigen Sie, sehr geeherter Herr! Es it jetzt leer.

A machined and polished aluminum block (6061T) will get equal to or better than the 99% reflectivity of the collar across the spectrum?


----------



## Enderman (Mar 5, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> A machined and polished aluminum block (6061T) will get equal to or better than the 99% reflectivity of the collar across the spectrum?


No, only precision dielectric coated glass or silver coated diamond-turned reflectors can get anywhere near 99%.
Polished aluminum in the best case is 95%.
Polishing would also decrease the surface accuracy, and normal machining will not give an accurate surface finish.
You need to electroform the reflector or have it diamond turned.


----------



## Genzod (Mar 5, 2018)

*Re: Phosphor conversion of photons in LEDs*



Enderman said:


> No, only precision dielectric coated glass or silver coated diamond-turned reflectors can get anywhere near 99%.
> Polished aluminum in the best case is 95%.
> Polishing would also decrease the surface accuracy, and normal machining will not give an accurate surface finish.
> You need to electroform the reflector or have it diamond turned.



Enderman! I've followed your two light cannon builds with much interest! Thank you for contributing here. You lumen-wizards will make a photon-professor out of me yet!

Out of curiosity if you know (I imagine you would), which would be cheaper to do--contract for one electroformed reflector to 99% or silver coat one diamond turned reflector?


----------



## Enderman (Mar 5, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> Enderman! I've followed your two light cannon builds with much interest! Thank you for contributing here. You lumen-wizards will make a photon-professor out of me yet!
> 
> Out of curiosity if you know (I imagine you would), which would be cheaper to do--contract for one electroformed reflector to 99% or silver coat one diamond turned reflector?


Hahah thanks 

Diamond turning is very expensive and usually only done for stuff like making mandrels.
Electroforming is a much more budget option, but only if the electroforming company has an already made mandrel for the reflector size you need.
Making a custom mandrel will cost like 5-10k, so you're limited by the stock options (with the option of having the reflectors cut to smaller sizes too if you need)
Unfortunately neither optiforms not phoenix have spherical reflectors of the size or angle we need, I may try contacting phoenix to see how expensive it would be for them to make a custom spherical one.

For the electroformed optics the silver coating is best with ~98% reflectivity but is very delicate, so unless you have it in a completely sealed enclosure it needs to have a protective coating on it making it even more expensive.
Aluminum coating is ~92% reflectivity and more durable, also cheaper.
Rhodium coating is what people use for short arc lamps that emit UV and need a durable reflector, but the rhodium is less than 85%.

If you get glass reflectors then you can have stuff like cold mirror or dielectric coatings which are 95-99% but glass is also more expensive and delicate.
The reason a cold mirror is ideal for collars is because all the infrared low wavelength light emitted is not reflected back, and this reduces the amount of heat increase due to the collar.
This low wavelength light does not increase the brightness at all and just heats the LED up needlessly, and more heat means lower output.

There is, as you noticed, also light that leaks through the cold mirror, which could theoretically still be used to increase intensity.
Leds however don't output that much infrared energy so I'm curious if using a solid metal collar reflecting all energy back would actually increase or decrease performance.


----------



## The_Driver (Mar 5, 2018)

*Re: Phosphor conversion of photons in LEDs*

My comment concerning the price of aluminium vs glass was based on production of larger numbers of aluminium reflectors. I don't think electroforming is needed for such a collar.

The glass variant from Wavien with dichroic coating leads to highest perfromance, yes. But 5% more output for 4x the price is rarely needed. I think they should have sold both variants.

The light loss in the Wavien reflector should not be of concern. It has a reflectivity of around 95% if it has a standard cold mirror coating. 5% of the output of a XP-G2 is around 50lm. Thats very easy to see, but it doesn't make much of a difference.


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## Genzod (Mar 5, 2018)

*Re: Phosphor conversion of photons in LEDs*

*Saabluster* said an aluminum core reflector would work, but also added a _painted _reflector would not. I'm thinking in terms of measured albedo, and I know for white acrylic paint, the albedo is 80%. That's not far removed from 85-95% for coated reflectors. My point isn't to use white paint, but simply say, does the argument about efficiency really boil down to what Saabluster said, yes or no, all or nothing?

If you take the Wavien collar *Sven_m* used in his experiment, the gain mathematically described is (0.75*0.4+0.25)/0.25=2.2. That means 40% of the wasted light (light predestined to not make it directly through a lens) is reflected back to the die and is redirected out the opening toward a lens. 

Assuming the reflector's reflectance efficiency is 99%, we can rearrange the equation as [0.75*(0.4040)**0.99*+0.25]/0.25=2.2 to say the same thing, but identify where the reflection efficiency plays its role. 

Now if you have a glass or PMMA bubble with a 60 degree beam opening, and you paint the outside with acrylic paint so the interior surface looks smooth, the equation becomes [0.75*(0.4040)*0.8+0.25]/0.25=1.97 That's only a 10% loss in performance over the wavien collar.

So how is it reflector paint won't work, when white paint only has a 10% performance loss? 

Keep in mind this isn't an assertion! It's a construct designed to give us a medium to dissect and analyze so we can bring out the actual truth. I think I might understand why it won't work, but I'd like to bounce it off everyone here to get a better understanding of the dynamics of the light in the LED and collar.


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## Genzod (Mar 5, 2018)

*Re: Phosphor conversion of photons in LEDs*

It would be extremely helpful in dissecting the above argument if someone has a link to anyone who has actually experimented with an aluminum core reflector _and obtained gain results_ by experiment.


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## The_Driver (Mar 5, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> *Saabluster* said an aluminum core reflector would work, but also added a _painted _reflector would not. I'm thinking in terms of measured albedo, and I know for white acrylic paint, the albedo is 80%. That's not far removed from 85-95% for coated reflectors. My point isn't to use white paint, but simply say, does the argument about efficiency really boil down to what Saabluster said, yes or no, all or nothing?
> 
> If you take the Wavien collar *Sven_m* used in his experiment, the gain mathematically described is (0.75*0.4+0.25)/0.25=2.2. That means 40% of the wasted light (light predestined to not make it directly through a lens) is reflected back to the die and is redirected out the opening toward a lens.
> 
> ...




The equation does not make any sense to me!

The LED is de-domed, so it is a lambertion emitter. 75% of the total amount of light that exits this LED hits the collar. The remaining 25% goes through the hole in the collar. The blue content of this 75% enters the phosphor again (minus reflection discussed above) and is converted and exits the phosphor in a different angle. This leads to an increase of 120% of the 25% of the light which I already mentioned. The gain of 120% will vary from LED to LED, also depending on drive current, heat, tint etc. It has no direct mathematical relation to the amount of angular light that hits the collar.

Where do you get your 40% figure from?

Any standard reflector of the same shape will work. The performance will only vary slightly depending on the reflectivity. The larger the size difference bwteen reflecotr and LED diameter becomes, the more precise the reflector needs to be.

Photon in the German forum tried selfmade stainless steel collars a few years ago. They worked, but not very good. Why? Because stainless steel only reflects around 30% of 450nm light. Low gain wa salso caused by the larger hole on the top, by the fact that he polished them instead of putting on a real coating, and imperfect shape, small collar size, sub-optimal led tint, maybe imperfect focus etc.. 

Concerning paint:
Easy test for you: take a focussed flashlight and shine it at the kind of surface you are describing (in the dark). Does the reflected "beam" throw as far as the flashlight does by itsself? You can be more precise by using a lux meter. You will have the same losses with a spherical shaped surface. I can't in any way imagine how white paint would ever work!
Reflective silver-colored paint would certainly work, but it will not be as smooth as a real reflector. This reduces the effective surface area so not all of the available light will actually hit the LED. In addtion to this the (probably lower) reflectivity needs to be accounted for.


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## Genzod (Mar 5, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> The equation does not make any sense to me!
> 
> Where do you get your 40% figure from?



40% of the light hitting the collar is added to the opening. 40% * 75% = 30%

This is the 30% of total light you need to make the added 120% you mentioned, as 30% / 25% =120%


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## Genzod (Mar 5, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> Concerning paint:
> Easy test for you: take a focused flashlight and shine it at the kind of surface you are describing (in the dark). Does the reflected "beam" throw as far as the flashlight does by itself? You can be more precise by using a lux meter. You will have the same losses with a spherical shaped surface. I can't in any way imagine how white paint would ever work!
> Reflective silver-colored paint would certainly work, but it will not be as smooth as a real reflector. This reduces the effective surface area so not all of the available light will actually hit the LED. In addtion to this the (probably lower) reflectivity needs to be accounted for.



If the albedo is 80%, it's obvious throw would decrease. I imagine someone has already taken a lux meter to acrylic paint and measured 80% reflectance. But the point was never to use white paint, just illustrate numbers.


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## Genzod (Mar 5, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> Photon in the German forum tried selfmade stainless steel collars a few years ago. They worked, but not very good. Why? Because stainless steel only reflects around 30% of 450nm light. Low gain wa salso caused by the larger hole on the top, by the fact that he polished them instead of putting on a real coating, and imperfect shape, small collar size, sub-optimal led tint, maybe imperfect focus etc..



I remember reading exactly what you just said here about stainless steel. It's a completely valid point that demonstrates albedo might be high but the important components of the light getting absorbed by the reflector render the albedo by itself misleading.

What is the ratio on blue photons to yellow photons in the white light headed to the wavien collar?


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## The_Driver (Mar 6, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> 40% of the light hitting the collar is added to the opening. 40% * 75% = 30%
> 
> This is the 30% of total light you need to make the added 120% you mentioned, as 30% / 25% =120%



The conversion process is probably not a constant for all LEDs and setups. I wouldn't use this equation. A LED with a reddish tint (less yellow-green) might work better for example than one which already has a very yellow-greenish tint. Who knows...



Genzod said:


> What is the ratio on blue photons to yellow photons in the white light headed to the wavien collar?



This ratio cannot be easily stated. It depends on the specific LED that is used. Just take a look at the spectrum of any standard cool-white LED (in the datasheet). Chemically de-domed Cree LEDs have a little bit higher-yellow green content. But these are not needed, the Osram Black Flat (it comes from the factory without the dome, no greenish tint) also works nicely.

To do this you would need to have the measured watt output of the LED (not lumens!) and then put it in relation to the absorbance spectrum of YAG:Ce Phosphor. After this you would apply the conversion loss factor for this type of phosphor. Then you would get the watts that come out after conversion.


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## Genzod (Mar 6, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> The conversion process is probably not a constant for all LEDs and setups. I wouldn't use this equation. A LED with a reddish tint (less yllow green) might work better for example than one which already has a very yellow-greenish tint. Who knows...
> 
> 
> 
> ...



I'm only analyzing one set-up, the Wavien collar and XP-G2, so to clarify, I'm asking if anyone knows the yellow to blue ratio in the XP-G2. The equation is not being used as a general design tool, only to set up discussion and analysis of the dynamics in one set-up. I'm not trying to assert it is correct or useful. I already mentioned I see one thing that might be wrong with it.

The equation is accurately describing the portioning of light in the set up. It _is_ sending a surviving 40% of the lumens involved in recycling/reflection part out the hole for a 2.2 gain. 

The equation does not (yet) accurately describe the specific details of the dynamic between the reflector and the LED. That is what I'm trying to investigate. The (0.40)*(75) component can be expanded to depict the specifics of the dynamics, like average number of reflections between the LED and reflector, blue to yellow conversions and corresponding heat losses, etc. That is the reason I am asking what the blue to yellow photon conversion ratio is in the XP-G2, so I can start to modify the equation to account for losses.


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## Enderman (Mar 6, 2018)

*Re: Phosphor conversion of photons in LEDs*

The 40% collar efficiency is pretty accurate.
Even between different LEDs most of the light is in the visible range and won't change the output much whether it is warmer or cooler colour temp.

What is more difficult to estimate is how much light is recycled by angle.
The areas of the collar closer to vertical will be reflecting light almost straight down, so more light would exit the collar compared to light being reflected from the side of the LED.
However, the majority of an LED's total output is emitted at 45 degrees.
Having a collar with a 30 degree opening rather than 60 would therefore give higher intensity, however it is impossible to know how much more without testing because of the non-linearity.

Of course this would only apply to custom made collars, since all wavien collars are 60 degrees only.
I guess they found this to be a good compromise between lumen output and intensity increase.


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## Genzod (Mar 7, 2018)

*Re: Phosphor conversion of photons in LEDs*



Enderman said:


> What is more difficult to estimate is how much light is recycled by angle.



Indeed. I would need a plot of the incidence verses %reflection for a bare, rough, phosphor/silicone surface for that. While I've seen that for glass, I'm doubtful one exists for a hobbyist's dedomed LED.


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## The_Driver (Mar 7, 2018)

*Re: Phosphor conversion of photons in LEDs*



Genzod said:


> Indeed. I would need a plot of the incidence verses %reflection for a bare, rough, phosphor/silicone surface for that. While I've seen that for glass, I'm doubtful one exists for a hobbyist's dedomed LED.



I have not found exactly what you are looking for, but I am getting closer:

Investigation of the Optical Properties of YAG:Ce Phosphor

Measurement and Numerical Studies of Optical Properties of YAG:Ce Phosphor for White Light-Emitting Diode Packaging

*EDIT:*
Page 130 of this book is interesting in this regard.


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## Genzod (Mar 7, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> I have not found exactly what you are looking for, but I am getting closer:
> 
> Investigation of the Optical Properties of YAG:Ce Phosphor
> 
> ...



I appreciate your efforts to help me refine my work, Driver.

The first paper I found a few days ago and I haven't yet fully digested it. The second is new. The Mie Theory calculations look interesting, but since that is new, it will take me a while to digest it as well.

You added the edit for the book while I was looking the second paper over. I'll give that a look as well. Thank you.


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## Genzod (Mar 7, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> Page 130 of this book is interesting in this regard.



There was no p 130 in the preview, but I went to the English version on Google and found on p 104 *figure 3.36* which provides coefficients that I'm interested in verses volume fraction of phosphor in LEDs. I believe there is an optimal fraction for LEDs like the XP-G2. Do you know what that tends to be?


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## The_Driver (Mar 7, 2018)

*Re: Phosphor conversion of photons in LEDs*

No, and I think Cree would really prefer to keep that a secret . Maybe we will find out at some point though.


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## Genzod (Mar 7, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> No, and I think Cree would really prefer to keep that a secret . Maybe we will find out at some point though.



That's interesting. I thought I saw a paper recently that determined the optimal fraction, around 20% if I'm not mistaken. I can't remember where I saw that, but I remember they produced two plots that they made that conclusion from.


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## The_Driver (Mar 9, 2018)

*Re: Phosphor conversion of photons in LEDs*

BTW: I just noticed something interesting. The Osram Black Flat, which doesn't have a dome, is very smooth on top of the die. It seems to be much more reflective compared to to chemically de-domed LEDs.


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## Genzod (Mar 10, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> BTW: I just noticed something interesting. The Osram Black Flat, which doesn't have a dome, is very smooth on top of the die. It seems to be much more reflective compared to to chemically de-domed LEDs.



Yes, and I believe the XP-G2 and XP-G3 surfaces are now intentionally roughened to change the angle of incidence at the surface for internal photons trying to get out. That works to our advantage with a wavien collar.

One might use a silicone sealer in discrete bursts to create a roughened surface. Be interesting to see if it would improve the performance of a collar and Oslon Black Flat.


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## Genzod (Mar 13, 2018)

*Re: Phosphor conversion of photons in LEDs*

I know that in the original waiven collar, there is a specific reflection efficiency--95 or 99% depending on who you ask (not important for the moment). It looks like this light is getting transmitted through the collar rather than absorbed even though I'd venture a guess the collar is getting very warm under a barrage of nearly 1000 lumens. What is important to me though is, it is lost and does not return to the die. 

When the light goes back to the die, it enters the silicone/phosphor matrix through refraction, even to some extent at a horizontal angle because there is still refraction at that angle of approach. The blue photons are said to undergo conversion to yellow photons to some extent and the energy difference between the two wavelengths gets converted to energy (heat) according to the Planck-Einstein relation E=h*c/λ, and the photons bounce around inside the matrix until they get "recycled" and find an angle out. Chance of direction is 25% out and 75% back to the collar.

I'm wondering of what photons that go into the die's matrix, what percentage comes back out? 

I realize each phosphor/silicone die has a different concentration ratio, making _one_ exact figure impossible for so many different compositions, but that doesn't preclude a generalized range in the optimal ratio that dies tend to be made at around 10-20%. For example, we may have a coated reflector with unknown efficiency, but if we know it was electrically coated by a manufacturer, we can say it is most likely in the range of 85-95%.


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## JacksonXI (Mar 22, 2018)

normally the phosphorus layer absorbs specific wavelength and then re-emit the light. if the LED chip is poorly design, leakage may occur


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## Genzod (Apr 22, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> The Osram Black Flat's luminance has been measured by multiple people and several record braking throwers have been built with it. The highest value ever measured (that I have seen) is 260cd/mm^2 at maximum output (4.5-5A). In the light linked in my sig we got up to around 240-250cd/mm^2.



I'm back after a family related medical emergency. Been a month now.

The one case I've seen of a surface brightness test (on TLF) resulting in 250cd/mm2​ was tested at 4.5amps. Unfortunately the charts presented as images are no longer available. 4.5 amps corresponds to 891 lm on a scale leading to 937 lm max at max 5.5 amps from another source on TLF. If you increase the lumens about 5% to max, the surface brightness would increase from 250 to 263, had it been tested at peak. That's fairly close to the calculated 266cd/mm2​, where you take the Lumens and simply divide by Pi and the emitter surface area (1.122mm2​ in this case).


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## The_Driver (Apr 22, 2018)

*Re: Phosphor conversion of photons in LEDs*

Sorry to hear that!
I currently prefer Köf3's tests on BLF. He uses a new method for measuring. He measures the actual luminous intensity with a reflector and lens (always the same one) to get more realistic values (of single-die LEDs) by calculating back from that. It turns out that the LE UW Q8WP actually manages the same luminance (if you get a resonably good sample), but with a bigger die and thus more lumens. Also just recently Osram announced new LEDs which are basically updated versions of these models which are more practical (center solder pad is neutral, no missing corner on the die, die not offset etc.).


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## Genzod (Apr 22, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> Sorry to hear that!
> I currently prefer Köf3's tests on BLF. He uses a new method for measuring. He measures the actual luminous intensity with a reflector and lens (always the same one) to get more realistic values (of single-die LEDs) by calculating back from that. It turns out that the LE UW Q8WP actually manages the same luminance (if you get a resonably good sample), but with a bigger die and thus more lumens. Also just recently Osram announced new LEDs which are basically updated versions of these models which are more practical (center solder pad is neutral, no missing corner on the die, die not offset etc.).



That's great to hear. 

Post #19 at BLF is where I get the surface brightness is 250 cd/mm2 ​@4.5A. I get my 891 lm @4.5A, 937 max lumens @ 5.6A and 1.122mm^2 die size figures from Köf3's tests. The *π *divisor I use to obtain surface brightness from lumens and die area comes from the limit analysis I explained here. 

My point isn't which of the many measured surface brightnesses is more correct than the others, but rather that the method of determining surface brightness with that limit is. You can see using the numbers the result isn't far removed from these measurements when they are compared at the same amperage.


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## The_Driver (Apr 29, 2018)

*Re: Phosphor conversion of photons in LEDs*

Yes, dividing the Lumens/mm^2 by Pi is the the formula for the lambertion emitter which a de-domed LED basically is. It gives a very good ballpark value! I have tried it before and is always close, but never 100% precise.


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## Genzod (Apr 29, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> Yes, dividing the Lumens/mm^2 by Pi is the the formula for the lambertion emitter which a de-domed LED basically is. It gives a very good ballpark value! I have tried it before and is always close, but never 100% precise.



Exactly the same problem you have with hobbyist measurements. .


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## Enderman (Apr 30, 2018)

*Re: Phosphor conversion of photons in LEDs*

Hey The_Driver can you do two simulations of a thick vs thin lens of the same diameter in your 3d ray tracing program?

Genzod claims that the reason the UF-T20 from vinh gets 260kcd is because the equation of lens area * led intensity is incorrect for thicker lenses.
With 250cd/mm^2 and 32mm diameter the result is 200kcd without taking into account transmission losses.

He says that the correct equation is 

I(cd)= T*sin2(A)*L*(d0/s0)2

T=transmittance
A=half the internal beam angle or arctan[Di/2/(BFL+x0
L=total raw lumens available in hemisphere.
d0=object distance
X0=EFL2/X
Xi=di-EFL
EFL=BFL+CT/n
S0=die dimension

However this gives incorrect lux values for pretty much everything else I've tried that isn't the L20, and also implies that using a thicker lens will give more lux than a thinner lens at the same diameter.
This doesn't make any sense to me because the brightness of the LED would need to be amplified when looking at the lens from a distance, more than simply reflecting/refracting using a typical reflector or lens.
Also the maximum candela has nothing to do with the size of the LED or the distance that the measurement is taken, so I don't know why the equation he is talking about even uses those values.

Please let me know what you think, thanks.


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## The_Driver (May 1, 2018)

*Re: Phosphor conversion of photons in LEDs*

I haven't gotton into lenses yet in the simulations. It might take me a while.

The equation has been proven many times over. The important thing here is that it can be applied from the Candela measurement back to the light. The lens can't be any bigger than 36mm if that is the diameter. You can't "cheat" this system.

I don't believe the 260kcd number with the current information regarding this light. It could be inaccurate for a number of reasons:

It's very, very difficult to get accurate optical measurements, 10% would be very good
The accuracy of a luxmeter always needs to be considered
Cheap luxmeters have problems with wavelengths at the edges of the visible spectrum (blue and red light) because of the shifted bell curve of their filters
The Osram Black Flat has a high content of blue light in it's spectrum, so the varriance between the values measured by different luxmeters should be higher compared to greenish de-domed Cree leds

Is 36mm really the actual optical diameter of the aspheric lens in this light? Does it have a coating? What type of glass is it made of?

The Osram Black Flat is sold in different Bins, but you never know which one you get and even then there is a high variance in performance between different LEDs. Maybe vinh got LEDs from a reel with a very high bin which nobody has tested before. Is his 260kcd the average of all his lights or the best one he measured?

Has anybody confirmed this value (measured in a reasonable distance) and also measured other ANSI-specified, unmodified lights with the same setup?

With the standard equation using 250cd/mm^2 and 92% transmission I get 234kcd for a 36mm lens. That's only 10% less than vin's value. It's not really possible to draw any conclusions from that. It's easily in the same ballpark.

You know, thinking about it, vinh sells a ton of lights based just on their luminous intensity. He really should be using a calibrated, high-quality luxmeter for his measurements (i.e. Gossen Mavolux, Mobilux etc.) and always comparing them with unmodified lights. He is a professional after all.


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## archimedes (May 1, 2018)

*Re: Phosphor conversion of photons in LEDs*

Please note, do not "copy-paste" from PM, and please avoid taking private disagreements public.


There is an Ignore function available for your use on this forum, should you wish to make use of that, but please do not involve moderation staff here in bickering among members.

Thank you all for letting it end, and moving along now.


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## Enderman (May 1, 2018)

*Re: Phosphor conversion of photons in LEDs*



The_Driver said:


> I haven't gotton into lenses yet in the simulations. It might take me a while.
> 
> The equation has been proven many times over. The important thing here is that it can be applied from the Candela measurement back to the light. The lens can't be any bigger than 36mm if that is the diameter. You can't "cheat" this system.


The lens is 38mm diameter but apparently there is a metal retaining ring which reduces the front diameter to 32mm, according to djozz's review.

I agree that it's probably a bad measurement by vinh, it just doesn't follow the laws of physics for a thicker lens to "amplify" the intensity of the LED more than a thin one.


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## Genzod (May 1, 2018)

*Re: Phosphor conversion of photons in LEDs*

If you want to have a conversation about thick lenses principal plane equations, can you title a new thread and begin it in another forum please. This thread is about Phosphor conversion of LEDs and photon recycling efficiency.

Thank you.


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## Greta (May 1, 2018)

*Re: Phosphor conversion of photons in LEDs*



archimedes said:


> Please note, do not "copy-paste" from PM, and please avoid taking private disagreements public.
> 
> 
> There is an Ignore function available for your use on this forum, should you wish to make use of that, but please do not involve moderation staff here in bickering among members.
> ...



Bears repeating. Read it, heed it. Won't be repeated again. Actions will be taken.


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