The XP-G3 and the mystery of the disappearing luminance

Awesome post, I understand it, thanks!

Thanks for the effort EasyB. Nice detective work. :+1:

Rather than having a flat layer of phosphor, the Xp-G3 has a sort of “dome” underneath the main dome which is filled with phosphor, this is how it achieves higher luminous flux.


And that’s also why it loses both lumens and intensity when shaved, you lose phosphor.
If you try to dedome it you would probably be left with the small dome on, which would give worse intensity than a flat phosphor LED.

Source is saabluster’s XP-G3 research on CPF.

Enderman, I don’t think that is true of XPG3s in general. Maybe he used some sort of solvent which redistributed some phosphor. With mine the phosphor is quite flat and I didn’t remove any of it when I shaved. Also, in the picture in this post I think it’s apparent it is just a layer.

Based on ceiling bounce tests I’m losing about 10% of the output upon slicing the XPG3. I lost a similar amount with the XPL V6 1A I dedomed. Now, with most of these XPLs I’ve been dedoming with gas, the dome does not come off cleanly and I’ve had to scrape the silicone off the die, so there is typically a small amount of silicone left on the phosphor, which I imagine lowers the output some. But I think even with a perfect dedome there is output loss. I know you have posted djozz’s test of an XPL V6 2C which shows practically no output loss upon dedoming, but I think that is the exception rather than the rule. I could be wrong though.

Thanks for the investigation EasyB, that was an interesting read, I never dived very deep in how leds are build up and you gave a clear summary, and why it is so relevant for flashlights. The experiments and measurements are fantastic, you must have a pretty steady hand for this led surgery! :slight_smile:

That’s a top down image, you can see there is some sort of glossy silicone in a circle shape within the yellow phosphor circle:

I marked with red pixels where I see the border of this “inner dome”
I am pretty confident if he took a side image of it we would see that it is not perfectly flat, it bulges. (unless the chemical dedoming process ruined the silicone bulge)

If the phosphor is mixed with silicone, (which is what the domes are made out of i think?) then dedoming might remove some of the inner dome which is mixed with phosphor, reducing the output.
Even if it didn’t touch the inner dome, simply having the bulging shape instead of flat would give worse throw.

From the XPG3s I have looked at and modified the phosphor layer is flat enough to be called flat, and I’m pretty sure I have not removed any phosphor from slicing the dome. And I don’t think the finite thickness of the phosphor is the cause of the poor throw performance, given what I have explained in the OP.

Have you dedomed any?
Chemical or heat?

I’ve only sliced.

I’ll emphasize one result that explains why the XPG3 is a poor thrower. The data in the last three rows in my table shows that 20% or more of the total light output is not coming from the die itself but from the light that has escaped the sides. The actual die luminance was unaffected evidenced by the X6 luminance being unchanged, but the total light output dropped significantly when the side-escaping light was blocked. You can’t expect to have high die luminance when 20+% of the output escapes to the sides.

I think we’re pretty much talking about the same thing…
Since it emits light to the sides that’s why they used a blob of phosphor rather than a flat surface, so that it goes over the edges and then produces the white light.
The first two images I posted have the die IN that dome, it is not simply the phosphor from on top of the die.
Here is a better image to explain:

You’re right though, dome shaving probably wouldn’t touch this phosphor dome.

I have dedomed a few XPG3s the phosphor layer is liquid like and not hard like the old style domes. Much easier to move around it doesn’t flake of?

When i done mine they where flat the bulge is from the LED die.

Thanks, I’m glad for this community that I can share my thoughts and work with.

I have gotten pretty good with a loupe and razor doing LED surgery. :slight_smile:

Kd/lm is fixed parameter for optical system&led combination.
If you have enough lumens but not happy with candelas - just change optical system.
Fresneles are good to focus big cobs like cree cxa tight, why not try them with side light distribution leds?

Fresnels are only good for very large diameters where an aspheric lens becomes too heavy or expensive.
Other than that, they are much worse than a single aspheric.
And no, the XP-G3 still sucks for any high intensity application regardless of the type of optic you use.

Surefire dont think so

I agree some sort of TIR could utilize all the light from a XPG3 and properly mix the colors to solve the tint shift issue, but it won’t solve the low luminance issue.

Yes there are ways to collect all of the light from an LED including that from the sides.
A regular flashlight reflector also uses 100% of the flux, if you count the spill.

The point is that the light emitted at the sides is not useful for increasing the surface intensity, which is what contributes to throw.
Throw is pretty much what this entire topic is about.

Here’s the intensity graphs of the G3 ad G2 overlaid:

G3 definitely emits more light to the sides, even though the difference is very reduced due to the dome being on when the tests are done.
G3 is red, in case that wasn’t obvious enough already :stuck_out_tongue:

Great ‘detective work’ here :smiley: I would have never considered that there could be such a significant amount of light from the side of the die. If that could be captured and sent downstream, the lumen loss could be mitigated but the tint issues would remain.

Phil

fwiw, some people are reporting tint shift across the beam, on their new Zebralight SC5C MK II H CRI, with Cree XP-L2
your post helped me understand that it is not an isolated incident:

[QUOTE=jruser;5106891]I got mine today from the new batch. Beam pattern is terrible. yellow hole in the middle of the hotspot, surrounded by decent tint hotspot, surrounded by yellow ring, surrounded by decent tint spill.

What causes this? reflector? LED? centering is fine.[/QUOTE]