testing a red XP-E, and comparing it to a red XR-C, 22/4/'14: XP-E2 results added in post #32

A bit hidden in this thread here I posted a quick output test of a red XR-E (it appeared to be called XR-C actually although the die size is more like XR-E ). I was told there that the XP-E was much better, but I did not have a red XP-E to test that. In the meantime I got one (from Fasttech), I put it on a 16mm Noctigon and did the test yesterday, the graph below also has the data from the XR-C I tested for the other thread. I do not have a clue what bin was used for both the XR-C and XP-E. The XR-C was a bit more to the orange side than the XP-E, now I found in my emitter-box another red XR-C that did have the exact the same colour as the XP-E (probably 630nm instead of 620nm), in series on the led-tester at 50mA the brightness of both XR-C's looks the same.

As usual, the emitters were tested outside a flashlight, mounted on a big aluminium block, directly connected to a bench power supply, a reflector placed on top facing the ceiling, output was measured with a lux-meter, of light bounced from ceiling.

So this is a test on a few emitters that have been around for quite a while and while the test could be more thorough (like finding out the exact bins), the differences are clear enough, and I believe there's a few people interested anyway.

The die of the XP-E is clearly smaller than the XR-C, if you measure the surface area, it is a bit over 30% less, so at the same output, the surface intensity of the XP-E die should be 50% more. The XR-C was on its aluminium board (copper does not give much gain over aluminium with the XR-C), the XP-E was mounted on a 16mm Noctigon copper board. (the second picture is a stereo pair, for fun).

So indeed this XP-E has all the advantage of the world compared to this XR-C: lower Vf with higher output, higher max. current, smaller die for better throw, and there are dedicated copper boards available (although you can mount the XR-E on a MT-Noctigon).

I hope there's someone who finds this useful. (I have not seen any red XP-E2's in the wild yet, by the way. EDIT: I see now that cutter has the red XP-E2, too expensive for me to order there, but they are around, at least).

Great coincidence. I just ordered a couple of red xp-e emitters to try out.

Interesting to see they top out at about 2A, thanks.

Those results match up just about right with what my very primitive light meter and visual measurements told me: 1.9A is just about the sweet spot for the red XP-E mounted on a direct thermal path copper MCPCB. At 2.2A it didn't get much brighter at all and I didn't try 2.5A. I've been sticking with around 1.14A on the thin aluminum MCPCB.

This red XP-E led got 3.6A for a moment by accident (at the end of the test), and it seemed to have suffered a bit, after that, at 2A the output went down from 237 to 226 lumen, at 1 A it went from 153 to 144 lumen. That is nothing serious, but I have not seen any sensitivity at all to this amount of over-current with white leds.

good info
thanks i needed that info
very helpful

It would be interesting to see how much better the xrc on a noctogon would do given it’s much larger solder point.

Very interesting, thanks!

I did that test some time ago :-)

Here I compared two 'identical' white XR-E's, one on an aluminium board with dielectric layer, one on a MT-Noctigon. On copper, at 2A, the output is 10% more than on aluminium, the current at maximum output shifts from 2A to 2.4A, on copper at 2.4A you get 20% more output than on aluminium at 2A.

So, even if the red XR-E is mounted on copper, it will be still way outperformed by the red XP-E

I thought I saw something like that done with a white XRE somewhere and there wasnt much to be gained, but I cant find it..

Anyways, I dont think the XRE will do much better on copper. Certainly not better than the XPE.

Btw., digikey, mouser, cutter etc. stock the XPE2 in red but shipping is too expensive. Maybe we can talk RMM into buying a few and then distributing them? :P

/edit: I thought it was djozz who did the XRE on copper test.. and it was him, he just posted the link. :D

Are you sure the die of the “XR-C” is bigger than XP-E ? Have you tried dedoming the XR-C to see if it can give anything interesting?

I was not precise enough, the die of the XR-C is bigger, as seen through the dome, which is the most relevant to its use, it is what a reflector or lens will 'see'. Upon dedoming the dies may not differ that much ( I think they will still be different though)

Ok :wink:

I second the XP-E2 request. I’d be interested in them if anybody would sell them from say… Washington. :bigsmile: Especially now that the Gen 1’s are out of stock and I’m looking to make another order…

I have been taking notes.

Thanks for posting your results djozz. Good work.

BTW, your lumen numbers are probably bogus. Lumen numbers are done by weighting light output by the human eye response curve. Your lumen conversion constant was probably derived from measurements of white LEDs. Lux meter readings are also weighted by eye response, but the conversion constant will probably be different for colored and white light.

Comparing your red “lumen” numbers between the LEDs should give a reasonable idea of their relative outputs, though.

Which way would you expect the results to be skewed?

I suspect that the true lumen numbers will be lower. Or maybe higher.

Fair enough.

Visually the red lights appear brighter to me than their lumen numbers suggest.