Production CREE XR-E Testing

NewBie

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Production CREE XR-E Testing (SLOW lots of pictures!)

First off, CREE made a vast improvement in the Vf of their LEDs, and it holds quite well with increasing current. In fact, I know of no other power LED company producing LEDs with Vf's this low. Why does it matter? Power consumed is Current * Voltage. So, here is the first chart, compared with a Philips LumiLEDs Luxeon K2, their latest device:

creexre.png



Next, I measured the lumen output (I figure accuracy is +/-10%), vs. current:

creexre2.png



This is also a vast improvement vs. any other LED I've tested to date, and pretty much, producing roughly 2x more light than other similar LEDs at the same current. Or looking at it another way, at the same light output, this part consumes about half the current, so your batteries will last 2x as long, and the LED will produce half the heat.

Due to the extra low Vf, and the outstanding amount of lumens comming out of the device at a given current, when you multiply these two together, the total power is often less than half, compared to most devices.

The extra high lumen output of this device, vs. power consumed, means it is more efficient, and more of you power leaves the device as light, instead of being converted to heat. Heat is the bane of LEDs and reduces both their expected lifetime and lumen output.

Yes, you can find the rare unobtainium bin of some whizbang Philips Luxeon, but they are rare, and still won't come close to matching the lumens vs. current of the CREE XR-E. CREE also makes some premium bins, this one tested here is just a run of the mill part.

For testing, the device was directly soldered to a 2" by 3" plate of 0.162" copper slab, and set on a table with no cooling air. Your results may be better, if you are more agressive in your heatsinking.
 
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dat2zip

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Wow, that's totally impressive up to 2A. Amazing!

I can't recall, but, I'm wondering if the datasheet has any information of output vs heat? Just curious to know of the thermal degradation versus temperature is relative to the competition. I wonder if the Cree die is better or worse in this.

My question is this? Assuming you could drive it at say 2A and die temperature rises to 120C as an example. Would it be better to drive it at say 1.5A and have a lower temperature die rise. It's possible that the same light configuration might produce more lumens at the lower current since it doesn't get as hot. There might be a sweet spot that increasing current to LED might generate less lumens output when the light gets to thermal equilibrium.
 

x2x3x2

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do u happen to have a shot showing the beam profile from the bare emitter?
 

McGizmo

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Nice graphs Newbie! I was told the die is rated at 2 amps but the lumen maintenance and packaging are not up to this current.

Some might falsely assume that twice the light means 1/2 the heat. Instead of lumens, it would probably make sense to measure the light in radiometric power and get a feel for the light output in watts and compare that to the input power of watts to get an idea of the actual power in heat generated. I suspect that in some cases, a light with the XR-E and a good MCPCB may deliver more heat to the flashlight host than a Luxeon driven at the same power level. The low thermal resistance of the Cree XR-E and MCPCB may be low enough to bring this about, relative to the Luxeon. Anyone soldering one of these LED's will appreciate how well the heat transfers throughout the package!

Any idea of Vf shift as a function of temp? I think that flat curve shows the difficulty for a DD set up. There is one DD composition though that I bet would be real viable and that would be on a single CR123.
 

dat2zip

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I found the thermal information on page 3 of the current data sheet.

-Wayne
 

cy

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WOW! what impressive gains!

2x performance increase from same power, seems the next paradigm shift for LED's has occurred.
 

light_emitting_dude

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Jarhead? Sounds like Marine Corps terminology! If so Semper Fidelis!! Will be interesting to see the new flashlights with this new LED!!
 

CM

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Nice. Thanks for the data.

This is what I got with one sample. Bin WF-P2

Vf(V) ILed(A)
=========
2.7 0.01
2.75 0.02
2.8 0.04
2.85 0.05
2.9 0.07
2.95 0.09
3 0.11
3.05 0.14
3.1 0.16
3.15 0.2
3.2 0.22
3.25 0.24
3.3 0.27
3.35 0.29
3.4 0.33
3.45 0.39
3.5 0.45
3.55 0.52
3.6 0.59
3.65 0.64
3.7 0.7
3.75 0.8
3.8 0.88
3.85 0.95
3.9 1.03

Theta Jc for XR-E is 8 C/W and the K2 is 9 C/W. I think if everything else allows, these can be driven to 1.5A like the K2. I prefer moderation where the incremental increase in current results in a somewhat linear fashion with the output which is 700mA or less which incidentally is how Cree specs their part.
 

ViReN

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Thanks *NewBie||Jarhead*...

It would be interesting to see the lumen's maintained over a period of time at lets say 1 A current.

Also, I do not feel there is much in overdriving the LED over 800 mA as the slope changes drastically after that current.

The Peak's Snow LED (5mm's based on Cree die) do not have good Lumen Maintenance record over 40 mA.

But I must say, Cree XR-E are an edge over any of the currently available LED's. Imagine 90 lumen's at 400 mA current... WOW ;)

MiniMag LED already has a deep reflector, now what we need is to mod it with a Cree LED and AR UCL, and we would see it putting out around 90 lumen's easily.
 

Pinter

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I also got higher values for Vf.

Cree XR-E, bin WC-P4, right out-of box, epoxied to heatsink. Measured on the emitter. Current source: nFlex.

20 mA - 2,71 V
58 mA - 2,84 V
100 mA - 2,94 V
175 mA - 3,05 V
350 mA - 3,24 V
500 mA - 3,34 V
700 mA - 3,49 V
1000 mA - 3,59 V

Last one is a little suspicous, I will check it later, maybe I was blind and missed a segment on my multimeter.
 

chimo

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Great data Newbie!

Wow, this is more than an incremental improvement - more like a leap. Looks like Cree has a real winner here. The conformal phosphor coating is icing on the cake (no pun intended).

It's VI curve looks like it would resemble a UxxH LuxIII (but with a greater light output). Luxeon did not do themselves much of a favour in releasing the K2 with such high Vfs. It was a more of one step forward and two steps back.

Paul

Correction: Oops - I was looking at the wrong point (500mA instead of 700mA) binning for the Cree. Looks like a good VxxH instead of a good UxxH bin!!! Outstanding.
 
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NewBie

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Pinter said:
I also got higher values for Vf.

Cree XR-E, bin WC-P4, right out-of box, epoxied to heatsink. Measured on the emitter. Current source: nFlex.

20 mA - 2,71 V
58 mA - 2,84 V
100 mA - 2,94 V
175 mA - 3,05 V
350 mA - 3,24 V
500 mA - 3,34 V
700 mA - 3,49 V
1000 mA - 3,59 V

Last one is a little suspicous, I will check it later, maybe I was blind and missed a segment on my multimeter.


Vf's will typically vary from part to part, but your Vfs are much closer to what I measured.

The reason why they are closer, is that it may be because you measured at the emitter for the voltage, typically, when you have current going down a test lead, it causes a voltage drop, which means voltages measured at the power supply will be higher than normal.

But remember, Vf's will vary from part to part, just like the Luxeons do.

Luxeon III binning current is 700mA
Your sample looks like it would be a Philips Luxeon III bin J.
My sample looks like it would be a rare Philips Luxeon III bin H.

@ 701.5 mA and half the voltage of a Lux V (3.2716
Volts), I'm getting ~134.075 lumens and 2.2950274 Watts.
This would make it a VXOH bin, and a very upper end of the flux bin at that.
 
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hakstooy

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I got some LEDs in and have been testing them and this is what I've gotten.

The ø data is output and is measured in an uncalibrated integrating sphere, so the units don't mean anything outside of relative comparison among the samples I've measured.

I'm using a current controlled source, and the voltage measurements are simply a rough estimate of the mean value measured during the spectral measurement. (Roughly 10 seconds to do)

Since I haven't built a real measurement setup, this is done simply by probing stars that are placed in air against the integrating sphere port.

LEDdata.jpg
 

Calina

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I put Newbie's data in an excel sheet, this is what I got.

Bear in mind that this is a graph interpretation since I didn't have the exact data so the results are aproximate.

V A W R Lm Lm/W

2,78 0,05 0,14 55,60 15 107,9
2,86 0,1 0,29 28,60 28 97,9
2,98 0,2 0,60 14,90 50 83,9
3,06 0,3 0,92 10,20 72 78,4
3,14 0,4 1,26 7,85 90 71,7
3,18 0,5 1,59 6,36 106 66,7
3,22 0,6 1,93 5,37 120 62,1
3,26 0,7 2,28 4,66 135 59,2
3,3 0,8 2,64 4,13 145 54,9
3,34 0,9 3,01 3,71 157 52,2
3,38 1 3,38 3,38 166 49,1
3,4 1,1 3,74 3,09 175 46,8
3,42 1,2 4,10 2,85 185 45,1
3,46 1,3 4,50 2,66 192 42,7
3,38 1,4 4,73 2,41 193 40,8
3,52 1,5 5,28 2,35 194 36,7


At 50 mA you have more than 100 Lm per watt, 5 mm LED don't do as well.
At .4 A you have about 70 Lm/W
At .6 A about 60 Lm/W
At 1 A it degrades to 50 Lm/W

You would need pretty agressive cooling to use the Cree above this level.
For a bicycle light it could still be useable since the air displacement is important but for a flashlight I would certainly not go above this level.

Thanks Newbie, great work
icon14.gif
.
 
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