Wow! Cree for the Amateur Modder

Well I had a swing at some Cree-placement of Lux III's today.
I first measured some P2-binned Cree XR-Es against my best (hand-picked from 6-10 contenders) Luxeons (a LuxIII and a LuxV) in my dodgy light box:


Cree P2(mean): 276 LBUs Vf 3.2 @ 700mA (3.29V at the LED)
Lux UWOK(best): 176 LBUs Vf 3.4 @700mA (3.4V at the LED)
Lux WYOS(best): 369 LBUs Vf 5.7 @700mA (5.9V at the LED)

Then I made up a Wiz2 convertor set to 917mA, and mounted the Cree in an Aleph light engine (easy, really: I snipped off the corners as others had demonstrated and then treated it like a Lux).
I then set this up in an Aleph 19 (which required NO modification to give a lovely, phosphor-yellow-filled reflector), and compared it to a U-bin LuxIII(previously hand-picked) at 1000mA in an identical setup (AW RCR123 in a single cell Aleph 19 with McClicky). Note that the McR19 is not a great "fit" for the LuxIII- the best position for the LED in the reflector is still not great.

Holy Cow! The Cree looks 50% brighter! Great solid spill and a blazing hotspot. Better throw too, with all those lumens!
The Cree setup pulled 1.15 amps at the batt to give 355 modLBUs as a torch, while the Lux, oddly, pulled 1.19 amps. It gave only 255 modLBUs.
The Cree has a very gentle vanilla hue, while the Lux is a classic XO bin.
These Crees seem to live up to all that I expected, and just a little more! This was lots of fun- M@gmods to follow!
Thanks for listening!
(And if there are any computer types who can tell me how to post pics off my website www.icudoc.com here, I will thank them!!! Update- I just fixed up the pics at the site but I am still trying to find a way to insert them here, even if not with Gallery).

Hmmm... Looks like you have Gallery2 installed, so your picture files do not have a standard .jpg extension... You won't be able to post the pictures here directly, but can link to them...

Click here for a link to the beam shot photo..

nice TV!

Are you sure Vf is 5.7V with the LuxV? Where are you measuring Vf?

My testing shows the Cree P2 at 930mA is just as bright as a W bin. Even at that current, the Cree consumes 30% less power. Driven at the same power, the Cree will be about 20% brighter than a W bin. We're talking X-bin Lux V territory here.

Wow, what a difference between the Cree and the Lux3.

For a second there I though the A/V component rack was placed inside the fireplace cavity.

CM said:

Are you sure Vf is 5.7V with the LuxV? Where are you measuring Vf?

Click to expand...

I believe it. I have a lot(about 50) of S bin Lux V and one of them has a vf that low. It is a WX0S. But just the one.

None of my P2's have such low forward voltage @750 ma.
Mine are all over 3.6 volts at anything around 750 ma.

Thanks for all the replies.
gregw thanks I'll try that maybe tonight.
CM, Anglepoise-the Vfs sure are low (at 700mA), but that was measured at the power supply, I didn't truely pop the Multimeter on the LED itself. Do you think that will change things? I'll have a look tonight, and get back to you.

ICUDoc said:

Anglepoise-the Vfs sure are low (at 700mA), but that was measured at the power supply, I didn't truely pop the Multimeter on the LED itself. Do you think that will change things? I'll have a look tonight, and get back to you.

Click to expand...

I don't pretend to be an expert on this but I believe that the closer to the LED one can get to the more accurate reading. Newbie maintains ( and I bow to his expertise in this area ) that wires soldered to the LED will change readings.
The closer to the LED the lower the forward voltage reading will be.

It would be very nice to have 3.2 fV @750 ma.

Anglepoise
I had a look at the LED Vfs with the multimeter tonight. As you said, they were all just a little higher when measured there, with the higher-powered LuxV exhibiting a 0.2V difference. Thanks for the education!
I am still impressed by the low Vfs of all of them, especially the Cree.
I have amended the post at the top to reflect this, and added the correct pics to the website!

The leads from the power supply to the LED will have an IR drop associated with it. Vf will be *lower* when measured at the LED because of this. It cannot be higher or your wires are have negative resistance :thinking:

A Vf of 5.7V is equivalent to a G forward voltage bin for Lux I's. That's very very rare. When measuring Vf, you need to be very accurate and precise about current *AND* voltage measurement. Any errors are magnified because the V-I slope is very steep. It will cause you to shift one or two bins in Vf if you're not careful.

Fair comment CM- I guess I am bound by the accuracy of the digital readouts from the power supply and MM, and by my leads' resistance. I might measure less and build more.....