Results: Testing XM-L, MC-E, SST-50, and XP-G emitters **Updated**



Thank you for a very scientific test! However, (there's always one of those) what about testing other emitters with the same methodology you used for the XM-L? I'm thinking specifically of the SST-50. As previously noted, 2.8 A. at the emitter is a sweet spot for the XM-L. Where does it start to nose over with the '50? Or the MC-E? People have opined that these two emitters are somehow obsolete, with the coming of the XM-L. I wonder if that is true. I could order some from Digikey (who ship very quickly), and have them shipped to you. You up for it?

Bob K


Since this is a rather recent hobby of mine, I have no experience with the SST-50 or MC-E. Has a test like this been performed yet for either of those two? I haven't looked. The main reason I wanted to do this test was because of all the heresay about the XM-L at >3a (including my own).

Thank you for the offer Bob. I'd be willing to test them though and can return them to you afterwards (pending they don't explode ).

The manufacturers are using the limitations of the battery technology to limit the current to there emitters instead of building high amperage drivers, a very cheap solution to an expensive problem. As battery technology increases I have three direct drive lights now that may burn out. The Ultrafire UF980L, The Manafont Drop-in and the KD C-8.

Excellent effort, Match, and it is much appreciated! I am sure this will be used as a reference for a long while both here at BLF and elsewhere. Keep up the great work. You are truly an asset to the group. 8)

Thanks for doing this test Match! I just got a Trustfire X8 and the most im seeing out of it is 2.56amps at the tail but it is quite bright and throwy with the deep reflector so im really happy with it. im wanting more deep reflectored lights but there does'nt seem to be too many around.

Okay, that non-linear part was bugging me, so I put the data on a regular graph and now I am much happier. This is a great test, Match. Now if I can only find a big block of aluminum with a lanyard . . .

It's not that way .The wattage the resistor must cope is E.I being E the voltage drop across the resistor and I the current.

An XM-L fed with one li-ion at 3A need 1W resistor...Vin 3.7V Vf at 3A =3.35V so 3.7-3.35= 0.35V drop X 3A = 1.05W the resistor being .35/3=0.11666 Ohm

Amazing work, match and foy ;) Looks like 3,4A-3,6A is the best for XML.

BTW, here you have a very good cell comparison:

The two MF Ultrafire XM-Ls I bought recently (the ones this group suggested) both measured roughly 2.8 at the tailcap using Panasonic 2400s for me. I wonder if you just got a flaky one or if maybe they changed drivers at some point.

What I've noticed is that the amps drawn seems to vary more with the battery I use than between the different XM-L drop-ins I test and remember; we're usually talking about max amps which is often direct drive. My XM-Ls have been fairly consistent and what Match said about DD in high mode is important. Every time I test for amps with these UF drop-ins, medium and low hardly vary at all while high is all over the place. Your Panasonic battery with your XM-L drop-in on medium or low might not be much different because those modes are regulated.


Great setup and great measurments, Match :)

I compared it to the Cree datasheet specs, and it matches quite well up to 2.5A, then your values are a bit below theirs (3% at 3A). I guess that's due to their measurement method: If I remember correctly, they only power the LED for a small fraction of a second to avoid increasing the junction temperature. (Unfortunately I can't recall where I read that.)


"Run in series, you have to have a resistor that will run the wattage of the light"

I understand perfectly what you say but just because the above sentence is incorrect what you get is the opposite. In parallel with the emitter the resistor must be much more powerful than one in series.

With an IMR 18650 or an IMR 26650 I get right around 4.5A with the MF UF dropin. I figured they were DD. I keep saying I need to swap the NANJG on my triple XP-G with this UF driver.

I'm perfectly happy with an XM-L @ 2.8A. Actually for a P60 drop-in I think less would even be preferable. I have some A123 LiFePO4 cells that I've been playing with and they turn the MF UF drop-in into a very reasonable light. It would probably be too underdriven for most (1.4-1.5A) but I'm quite comfortable with it.

This is quite possible. For consistancy, all measurements were taken exactly 10 seconds after power on, which also allowed me to get the current dialled into +/- 1ma. At higher power levels, it was quite apparant that output was dropping almost instantly due to, like you stated, junction temperature. Considering the difference between the test heatsink and a standard flashlight, I feel these losses would be considerable at high power in normal practice. One of these days I'll direct mount a bare emitter to the test platform for comparison.

Can someone please decipher arenat for me?


'Tis in English.

There's two ways you can connect a resistor. Across the LED (in parallel) or between one contact of the LED and the equivalent contact on the battery or driver. (In series)

Hope that is slightly more intelligible.

And since i forgot to say so:

Thanks Match for this!

I reckon that was an enormous amount of work so thanks for doing this.

Since my language skills are inexistent maybe posting what Match stated above some people can get it...

"The lumen difference for any torch or drop-in much above 3a woud be negligable outside a I.S. Any perceived difference would be almost entirely based on the reflector/lens combo. This is going to be my new wish from manufacturers...."Better xm-l reflectors, not more amps!"

Thanks Match!

...wait. wow...

I'm.. I'm.. actually satisfied with my current t6 dropin? no more lusting for higher current drivers, when 3A is more than good enough?

... whatever will I do now?

(seriously, thanks. You've laid that question to rest for good. I gotta ask though, since those 80 stars were for work, what would you have done if you'd blown them? Pushed back the project, or did you over-order 'just in case'?)

Why, go with multi-xml emitter setups of course, silly! :stuck_out_tongue:


(... I gotta ask though, since those 80 stars were for work, what would you have done if you'd blown them? Pushed back the project, or did you over-order 'just in case'?)


First rule of business: Why buy one when you can get two at three times the price! (bonus points if you know the movie that's quoted from)

I already had a few extra. After the first run and seeing no evidence of damage, I was content to try out some of the other 80 ordered.