dedomed a xm-l with success

ergotelis

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I don't have much time, i will write a few comments, later will post more details.
The led is a xm-l U2 2S from cutter, pure white color, was damaged during soldering, but dedomed with success. Can tell you how to do it with a good success rate. Same reflector, 7135 based driver same current, in a xeno F8V5 host:

Was a normal domed led in the flashlight,a xm-l U2 1A:
580 OTF and 9500 lux
now the dedomed xm-l,
488 OTF and 19450 lux!!!!!

Tint shift to ~4800K-5000K(!!!!) (as i said it is a U2 2S from cutter)
Looks slightly more yellow than 3S tint that i have, i think it is now in this category.

lost a 15% of light(assuming both were performing about the same,can't remember well, but i think they did perform the same in lumen testing before dedoming),got a neutral tint and got more than double increase in lux!

Now this is WOW!
 

Walterk

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Lame teaser, tell us more !

Did you remove the jelly dome in full?
Did you cut the dome off? How ?
 
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ergotelis

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I will try to dedome a third led in a while and i will give you all the info needed. The main idea of the method is with an oven or something to produce heat under the led. Not very high temperature, just the one needed to solder it to a pcb. Then the core becomes soft and delicate, with some press in specific points it is possible to dedome it with success.
I removed the whole silicon core, it pops out like in sst50/sst90.
I don't know why the color changed, we will have to ask someone more expert or try to find some more information about it. Will post some photos too soon, sorry for not having the time currently to complete all the details.
 

richpalm

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Had a T6 that got dedomed when the GD file slipped. Still works but got horribly green hotspot.

No more filing stars!
 

Illum

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The dome of certain LEDs do assist in shifting the color a bit. I once sheared off the dome by accident on a CREE XRE CW and the output turned NW
 

Walterk

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Maybe you could measure the lux@1 meter of the led only (without reflector/lens) before and after?
Now that would give me a lot more insight...
 

Harold_B

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Pardon me for not knowing better but I don't quite understand the excitement over building a light with a de-domed XM-L. The issue for me is the ~ 20% drop in output as measured in lumens (OTF). The higher lux readings are likely because the light from the die will be more directional. The LED is reduced in output due the loss of out-coupling efficiency for the light emitted at a high viewing angle from the die.

I would be interested in measured spectral data gathered using a photogoniometer (as opposed to an integrating sphere) to understand the color shift. The XM-L has a lot of color separation over the viewing axis so it won't be a big surprise that the color temperature would shift with the dome removed.

We have de-domed a few LEDs ourselves including the XM-L except that we want everything off including the phosphor layer. Several hours soaking in IPA does the trick along with a couple of hours spent picking chunks of silicone off the die. The real challenge is not scratching the die surface or damaging the wire bonds.
 

MikeAusC

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Pardon me for not knowing better but I don't quite understand the excitement over building a light with a de-domed XM-L. . . . . . The higher lux readings are likely because the light from the die will be more directional. . . . . .

I think you've answered your own question !

For some people the sole aim of building lights is to have the brightest spot, no matter how tiny it is.
 

Harold_B

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Well, perhaps so Mike. I understand the desire for a bright spot. That one is easy. Getting a brighter spot by making the LED more directional while making it less efficient (lowered output) might be more economical than capturing the low angle output and directing it to the spot using appropriate optics. It seems like a waste of potential output to me so I thought I'd ask in case I was missing something. Not that one approach would be absolutely right while the other is wrong, just asking a question.
 

RCantor

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Pardon me for not knowing better but I don't quite understand the excitement over building a light with a de-domed XM-L. The issue for me is the ~ 20% drop in output as measured in lumens (OTF). The higher lux readings are likely because the light from the die will be more directional.

The excitement is about increasing the throw in a LED that's more floody most of the time.

(Oops - too late!)

I have the need for both types of light. During the day I need to light up shadows 50 - 100 feet away so a small but very bright spot is exactly what I need for that light. It ends up being the single light I use most often but only because I can always choose from several lights for any night time task. :)
 
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ergotelis

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Guys, the challenge is that you can get in a P60 host 20.000 lux with quite a good number of lumen. Ok, you get a loss, but still enough lumen out there. In these small tactical flashlight hotspot in needed to be bright.
Harold, can you describe the procedure you did more analytically?
I will write about mine after i finish my third good success.( i have already 2 fails in the beginning, but i saw that heating the led to a high temperature helps the core to pop out)
My next step is to put the led@4amper in a 73mm reflector.
 

bmmeadors

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If we're looking for more lux in a P60 with little / no spill then maybe try an Ahorton's Aspheric.
If you are looking for less throw but with some spill then maybe try the Manafont (Ultrafire and sku: 6047) smooth parabolic reflector. There's a thread about it being used with an XP-E here. But I would think that it would give better throw than most P60 reflectors.
Whatever you decide to do with it, good luck, and please keep us updated. :thumbsup:
 

Al Combs

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I don't know why the color changed, we will have to ask someone more expert or try to find some more information about it.

There was a thread a while back that touched on the subject of color shift and lumen loss in an LED with its dome removed. The dome of a white LED reflects some of the light back onto the surface of phosphor covering the blue emitter. This reflection causes a secondary yellow or orange fluorescence (cool or warm) that increases the lumen output. The secondary fluorescence has no blue component because it is absorbed by the phosphor. The color shift is caused by the absence of this extra yellow or orange when the dome is removed. Or more precisely a higher ratio of blue than an LED that has a dome.

If you look at the typical cool white LED's relative spectral power distribution graph in the data sheets, there is a transmission peak at ≈460nm that is about double the intensity of the level at 555nm. Significant enough to cause a color shift in its absence. The eye is much more sensitive to changes in color than intensity.

Someone in this other thread argued a reflection couldn't possibly increase output because there are no new photons being created by the reflection from the dome. Fluorescence is never 100% efficient. It can't create a beam of light more energetic than the original excitation source. It would be more beneficial to multicoat the dome and let the would be reflection pass right on through.

What they didn't to take into account is the lumen is by definition an adjustment of radiant flux power levels against the human eye's sensitivity to different wavelengths of light or luminous efficacy. The eye is ≈17 times more sensitive to 555nm green (peak photopic sensitivity) than it is to 460nm blue. The secondary fluorescence isn't creating new photons but it is converting them into wavelengths easier for the eye to see.
 

Harold_B

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I would be inclined to argue that the color shift due to the back reflected photons from the dome is not correct. GaN materials (InGan, P-Gan, ...) all have a high index of refraction and absorption coefficient in the visible wavelengths. Basically, anything that is a good emitter is a good absorber. The reflectivity of the die can be calculated using the refractive index which is about 2.45 at 450nM and then generating a best fit curve based on the real and imaginary components of the Reflection Coefficient. At the angles the photons would be back scattered to the die the reflectivity is about 6 - 25%. Mostly less than 10% for any visible wavelength striking the die at 0 to 45 degrees.

The purpose of the dome is light extraction. Making the ray path from the die encapsulant exit surface perpendicular at as many points as possible increases the out-coupling. Removing the dome creates loss at the surface due to TIR. If the light should make it back to the phosphor layer and be reabsorbed by a phosphor chrystal it will be scattered isotropically. That is most of it, if not all will be scattered into the die. Some remote phosphor designs use light recycling schemes but there is typically a gap between the phosphor layer and the die or there is a filter that prevents the scattered light from being sent back toward the die surface.
 

MikeAusC

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If light from the phosphor crystal is scattered isotropically, then the percentage of light going outwards would be the same, regardless of whether the blue light came from the chip - or reflected back from the dome.
 
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