There is no substantial gain in throw going from dedomed XP-G2 to dedomed XP-E2

Flashlight Modding and DIY Parts
1

Some time ago I did a Uniquefire UF-T20 mod with a dedomed XP-G2 R5 (3C-tint) led on a Sinkpad at 2.95A (measured tailcap). I wanted to make a similar second pill for this light (using a 'C8 pill' obtained from Fasttech) with a dedomed XP-E2 R3 (1D-tint) led on a Sinkpad at 2.4A (measured tailcap), so I could make a direct comparison. (There is no gain in driving the XP-E2 any harder than at 2.4A)

Let's do the math first.

Using the famous emitter test results done by match, the emitter output for the XP-G2 at 2.95A should be about 785lm and the emitter output for the XP-E2 at 2.4A should be about 480lm. So (with XP-G2@2.95A and XP-E2@2.4A) XP-G2 puts out 1.64 times as much light. But the die surface of the XP-E2 is 2.2 times smaller than the XP-G2:

so the surface brightness (and thus the expected throw) of the XP-E2 at 2.4A is 2.2/1.64=1.34 times brighter than the XP-G2 at 2.95A. This difference is not huge, just slightly seen by eye, and you have a much smaller hotspot. In other words: there is no sound reason to go XP-E2. Even more, the XP-G2 can be driven quite a bit harder than the used 2.95A, that should be a much better upgrade .

But now abandon theory.

I did the XP-E2 pill anyway (dedomed XP-E2 R3 1D-tint on Sinkpad reflowed onto C8-pill with 7x7135 Nanjg-driver, measured 2.4A at tail):

Uniquefire UF-T20 beamshots compared, left the ddXP-G2 pill, right the ddXP-E2 pill (I made the left photo a while ago):

Measurements:

XP-G2-pill XP-E2-pill

lumen estimate zoom out: 490 lumen 260 lumen

lumen estimate zoom in: 332 lumen 179 lumen

throw at 1 meter, 1 minute: 106 klux 135 klux

throw at 1 meter, settled: 101 klux 128 klux

Looking at these numbers, when going from the XP-G2-pill to the XP-E2 pill, the difference in lumen output is 0.54 (the math said 0.60), the difference in throw is 1.27 (the math said 1.34). So the XP-E2 pill that I made (as compared to the XP-G2-pill) is performing a little bit less than the theory predicts, but I am actually quite happy that it is so close to the expected numbers (it is nice when theory and practice match).

A sad observation is that you loose a lot of light between the emitter and the outside world in a aspheric, even when zoomed out it looks already like around 40%, and zoomed in 60%. EDIT : sorry, I forgot that these emitters are dedomed, that gives at least 20% loss, so an aspheric's efficiency is not that bad after all .

My overall conclusion is that not just in theory, but also in the real world, when the goal is throw, there is not much gain in using dedomed XP-E2 over dedomed XP-G2. (unless you are especially looking for that extreme narrow hotspot, which sure is fun to play with )

2

Nice.

So the XPE is close to the end of it’s useful current draw . . next step is to add numbers with the XPG2 amped up to it’s useful limit nearing 4A or more? (please)

I’m pretty happy with the XPG2 in the SK68, but I’m itching to try the other one in something with a reflector . . just still not sure which host . . . was thinking of a P60 module . . . but maybe a C8 or similarly pocket-able light built to handle higher draw instead?

3

That was a really useful post djozz! THANKS!

For my type of use, this only confirms one thing. De-domed XP-G2 is as far as I am willing to go in terms of narrow beam, and “low-lumen”.

Do you know what the current was to the emitters in DD?

How would you rate de-domed XP-G2 vs XP-E2 (not de-domed)?

4

thanks, I am not sure what you mean with DD, I only measured tail currents, but these being 7135 based drivers, that is also supposed to be the led current, I hope that answers the question? About ddXP-G2 versus XP-E2, In another thread somewhere I posted this picture:

As can be seen, the enlarged led-die from the XP-E with dome (XP-E2 is the same size) looks about the size of a dedomed XP-G2, so in terms of hotspot-size I expect them to behave similar. I assume that dedoming costs 20% of the output (not sure how I got that number actually) but if you look at match's output graphs on Sinkpads the xp-g2 is 20% more efficient than the xp-e2 at 2A, so at that current they should perform similar. Under 2A the xp-e2 is more efficient, over 2A the dedomed xp-g2 is more efficient. All assuming Sinkpad use.

(and now to bed, zzz)

5

Sorry. I read your tail cap measurements and driver info. Yet i managed to think that dd was direct drive for a moment…
Just so used to dd being direct drive… :stuck_out_tongue: (I obviously stopped thinking)
dd was de-domed…

6

Great info and post djozz. Love the pictures too. Thank you.

Would it be correct to translate your findings into the following 2 general guidelines?:

  • If you’re going to push over 2 amps, go xpg2.
  • If using a small one or two cell AA or AAA host, go xpe2.
7

Well, that would be: if throw is what you want and you go over 2 amps, then a dedomed xpg2 works better than a domed xpe2. Not surprising when you know that xpe2 output completely levels out at about 2.5A.

And (regardless of dedoming) at low currents xpe2 and xpg2 differ not much in efficiency while xpe2 throws better. Actually I don't understand why for small flashlights that inherently (small reflector) have trouble with spot brightness the xpg is used massively, while for a minimal loss of lumens xpe gives a significantly brighter hotspot. I can't imagine the whole world want huge flood, so it must be again: lumens sell!

8

Good info. Thank you again.

9

I'd love to see the 'real life' performance of the XP-G2 on a Sinkpad in a well heatsinked host at 5A. But that is not going to happen in the Uniquefire UF-T20, it is not heatsinked for that amperage, and it is single 18650 and a driver that keeps the current well controlled at 5A with one (IMR) 18650 is as far as I know not around (yet). So someone else with a better host?.... (I am just not into big multicell Li-ion lights).

10

On a more general note: there is a few nice observations that can be derived from the fact that the surface area of the xpg is 2.2 times that of the xpe. Using match's Sinkpad data you can see that to obtain the throw of a xpe2 at max current (around 2.5A) you need to drive the xpg2 well over 5 amps. Or the other way around: to obtain the throw of a xpg2 at 3A (which is what I think a proven and not too over driven current for xpg2 on a Sinkpad) the xpe2 only needs 1.2 ampere.

But to put it all in perspective: the output (and throw) of the xpe2 increases only 50% when you go from 1000 mA to 2400 mA, only mildly visible and hardly worth the massive energy loss as far as I'm concerned. The same goes for xpg2: going from 2.1A to 4.0A you only get 50% more light.

I think it is fair to rename BLF : BOLF (budget overdriven light forum)

11

good info, thanks for testing and posting

12

Great stuff thx for posting.

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Yeah, 5A is OK, but 3.5 to 4A should be doable with IMR and I’m not sure the gains above that are worth it (to me). I could probably do a test rig with a DST reflector, but unfortunately I have no way to measure results. I also wonder if there is a reflector shape where the XPG2 outperforms XML for throw (not lumens) at that current draw level.

14

I don’t know what you are talking about djozz.
off to make some egg and bacon… … fried on a a few flashlights of course J)

:bigsmile:

15

Speaking about over driven emitters..

How does the XP-E2 on copper handle direct drive from an 18650 cell?

What kind of current is typical, and will the emitter easily die? 0:)

16

It looks that the way the xp-g2, xm-l2 and xp-e2 are build is very similar, so the bond wires in those three emitters I expect to burn at the same amperage (I tested it at 8-9 amps). The led die of both the xm-l2 and xp-g2 survive that current (although the die of the xp-g2 gives off much less light already compared to max output). I guess that in case of the xp-e2 the small die will give up before the bond wires burn, so you can see some nice light effects when trying that out (I haven't).

The Vf of the xp-e2 is similar to the xp-g2 and the current direct drive it on a 18650 will mainly depend on the cell, but I suppose it to be more than 5 amps. Not very useful since the maximum output is reached at about 2.5A, and I don't know if it is enough to destroy the die.

Ok, lots of thoughts above, and the answer is: I don't know

17

Thanks for you answer.

Ill try it out, but ill check emitter current with a battery that is partially drained first combined with a driver that has a tiny amount of resistance.

18

I’m planning to buy this light and try modding it. The option of leaving the original pill in tact and make a new one sounds nice to me, as it will be my first attempt at modding a flashlight. Any tips for that would be welcome :).

What would be the maximum power the heatsinking can handle? I was thinking about a (dedomed) XP-G2 on copper driven at about 3A. Would it be able to handle that for a reasonable amount of time?

How wide is the maximum flood with a dedomed XP-G2? Is it still a pretty wide angle, or does it get very narrow?