Cree XP-L V6 2C led, tested against XM-L2 T6 3C, edit23/7: I repeated the test and measured a dedomed XP-L

That is an effect that I would not expect to be so high, but perhaps it simply is that high and then it could be a cause of the output not dropping (it is dropping but the drop is just not measured in lux because green counts more than blue, in simple words :-) ). it would also mean that dedoming a cool white led might not cause a lumendrop, but dedoming a more neutral led will cause a lumen drop because in that case you convert more light towards the red area, out of the region of highest 'eye-sensitivity'.

I have the impression that my luxmeter is overly sensitive to blue because the blue XP-E2 that I tested, and also the blue die of the XM-L colour give unexpected high readings. If this is true, it would make your explanation less likely.

how do so many people produce clean results, while I always struggle to do it right and there's always flaws in the materials and methods that make the results ambiguous :-( ......

Ok, I ran the dome/dedome test with the XM-L2 T6 3C I still had from the test of the OP. First thing that was not perfect was that the die had a slightly darker spot somewhere. It was not much, and I went ahead with the led:

I did a fresh voltage/output test up to 8A, and with the led still hot I went for the dedome. And apparently the led had cooled down just a bit too much, a bit of the phosfor had come off, say 3%:

Here's the dome with the bit of phosfor:

And the die at 0.5mA, if you look well you can still see the dark spot as well:

Yeah, more variables than I need: does this extra blue add to the lumen-count or will it reduce it? I have the impression that my luxmeter favors blue a bit too much, but perhaps still not as much as green. The 'blue' region of the die occupies about 3% of the die, does that matter much for the test at all? I don't know, so I just went on to the second run testing, and will just dump the results on the net for you to decide what it all means :-( :

At least the dark spot on the die did not get any larger in the course of these tests (I checked afterwards).

So... if you ignore the phosfor damage as a factor involved in the readings, dedoming gave about 10% lumen loss, and has no voltage effects (you see only one voltage curve because the two curve are completely on top of each other).

I think I may carefully assume, perhaps (*sigh*), that 3% phosfor damage could not have counted for 10% light loss on its own, so dedoming a 3C does lead to lumen-loss. The XP-L was a 2C which is cooler, and in the reasoning started by led4power in the above 2 posts, dedoming that tint could cause less lumen loss, because more light converts to the area of maxumum eye-sensitivity by the dedome.

So nothing can be ruled out for certain, jay!


Or not.

(Not going to try this again, can I now just go back modding some flashlights, please? ;-) )

Thank you very much djozz. I know it’s frustrating when things do not go as planned.

Thank you also for furnishing us with your raw data despite the possible problems and your frustration. At a glance your assumption looks safe to me.

This is still very useful info. Only downside I see is not using a XM-L2 U2 1A, the only XM-L2 I dedome, and seems to be the most common dedomed. I've seen de-domed 3C's and they turn a pretty strong yellow - I got a bunch laying aroung here: 3 from a someone else's modded Shocker that I had to re-mod, and one that de-domed itself in one of my lights. The roughly 10% measured drop is interesting, but suspect a U2 1A would lose a little more. I've measured close to 20% from what I recall between domed and de-domed Shockers for example, at what should have been equal everything else.

How are you dedoming your emitters?

Gas - of course! "A Perfect Dedome?" ( Smile. The cut/heat method works of course, it's just more prone to error for me. I could view vinh's video a 100 times and I'm still unsure exactly how's it's done, or how to be sure to get consistent results. The gas method is very consistent. Dale is bringing up some good pts about possibly less tint shift using the cut/heat method, some may say less output loss as well. Since we lack accurate data on this, it's a tough call but hopeful sign, just don't have data or a technical explanation/theory on why.

If djozz still reports a 10% lumen loss on a XML2 1A, it would make me question if the heat method yields a lower lumen loss than petrol. But we’ll see… Of course to do scientific method he’d have to use both heat and petrol to de-dome the led and measure the lumen loss on both. Unless someone else has already done the objective testing though.

I even managed a hot de-dome on a Luminus SST-50. Color is still very good, appears to my eye to have gone more white from a bit blue/white, and the beam profile has a tighter hot spot. Still not a true thrower but it’s doing quite well now (except for the mass amounts of heat it’s making at 5.6A)

That one was interesting. The die is covered with a shiny seal even under the dome. That part is still there as is the dome window frame. Might need to pry that frame off now and see if tightens up the beam a bit more…

If SST50s are anything like SST90s you can just stick a knife in between the corner of the metal frame and the dome and pry the dome out cold. It’ll come out extremely clean.

and that slew of bond wires was a bit frightening! lol
I de-domed it with the light in Turbo mode, didn’t see it release like I do the XM-L2’s it just popped out.
Is the frame glued or taped down around the die itself? Wonder if it’ll pop off? But this one is in the big TK61 and I can’t get the head off that light, so I have to work down in the hole as it were.

I know I know, this was an experiment…

Thanks djozz. More great info.

Does the texture of the 2 dedomed emitters appear different in real life? It almost looks like the xml emitter appears more "flaky", but it's too hard to tell in the pictures. Here's a mouse over (xpl mouse out).

There appears to be a difference in the number of 'dots" between the 2 emitters. The dots are also clearer on the xpl. It almost appears that there is some type of coating on the xpl.

When I have collected enough motivation to go on with this, and I have bought two cool white (2C or 1A) XM-L2 leds, I could go for a petrol/hot dedome comparison. For the moment I want to do some mods again.

The texture of the XP-L die and the XM-L2 die/phosfor looks the same to me (yellow fine grainy stuff), just the 3C die has a thicker layer.

Thank you for the followup. I understand about needing to give this project a rest. You sure gave us a lot of good info to digest in the meantime.

Thanks again so much for this great contribution.

Thanks all for the kind replies, guys!

:start small rant:

I posted the first XP-L test also on CPF, and was cross-examined if what I was posting was real, that I had the wrong control led, and why should they trust a home made integrating sphere. All the arguments were valid in principle and I tried to answer the questions as well as I could, it took me a lot of effort, felt that I had to choose the words with a lot of care not to leave a wrong impression . There were however two things that bothered me: 1) all the arguments were theoretical, nothing wrong with theory but it would be so nice if also some people who were actually going to use the led found the post interesting, and responded, 2) there were two people who actually discussed the results and did not go straight into criticisizing the used methods and those were people who also post regularly on BLF (leaftye and Phantom23), perhaps because they had read more about the background of my testing over here, but I think it is not just that.

The thing is that I like posting here at BLF because my work is accepted as is, even if it is not perfect, and people just use the part that they find useful. And I can always count on some nice replies, with appreciation of the work. (I try to do that for other people's work too, but I regularly miss fine informative posts :-( ). I am now not going to post the further tests on the XP-L and these dedome tests on CPF because it will be another time-consuming effort just explaining the limitations and flaws of the tests (that I am perfectly aware of) and not also positively discussing the things that actually can be learned from them.

:end of small rant: (not meant to start another epic crusade on CPF (CPF has good sides too!), please don't start that, it was just something I had to say)

I agree with you, who would want to post data for people who seem to on a mission to discredit you just because you had the audacity to share with them, i like lots of accurate data, and of course we are not wealthy enough to own professional equipment but if we can do the next best thing that is accurate enough and reproducible and acknowledge its limitations but use it to its full potential then in my opinion we would be fools not to do so, and i really appreciate your data because we can ask questions and you answer them and are willing to make improvements and additional tests if we come up with any.

I should buy you one of these: Smile

I dunno - they are very nice and sweet to vinh... Smile

If I could point to one single person that has impacted our hobby the most, I would have to say djozz. Your crash testing showed us the potential of various emitters. We, and others, than built accordingly and began pushing to new levels that were not reached before. We started pushing drivers, hosts, etc. It's hard to quantify how much has changed as a result of your testing. I bet it is way more than you or any of us realize.

And, your work is the most precise we have here at BLF. Anyone that criticizes you here would need to put their money and time where their mouth is and show us better.

+1 totally... Hhmm - comfy had my top vote, but djozz is wayyy up there, very close for sure. Following in the footsteps of Match, Relic38, etc.

Unless the red ink is the blood of starving children I don’t think she would find them appetizing…

Love you guys, but let’s call it a day on the CPF stuff, no matter how well intentioned? djozz did say that he was just venting and didn’t want to start anything!