# How To Tell Cree Q2 from Q5 + Artifact (pic)



## lewong (Dec 5, 2007)

I just received 2 Cree XR-E Q2 (SKU 2662) and 2 Cree XR-E Q5 (SKU 2663) emitters on star boards that I purchased from Kaidomain. What’s the best way to tell the difference between the Q2 and Q5?

Also, in looking at the emitters with a loupe, one of them seems to have some kind of artifact near the emitter – see the attached photo in the upper left hand corner. Is this a manufacturing defect? Will this have an effect on the life or function of this LED?


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## jtr1962 (Dec 5, 2007)

The artifact is the result of the dome starting to detach. It's an internal separation of the silicon filler. If you push down gently on the dome you'll probably find that it mostly disappears. It shouldn't affect LED life. It might affect beam pattern slighty, however.


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## WeLight (Dec 5, 2007)

This is an indication the leds have been out of the vacumn sealed bag for some time and were not prebaked prior to reflow, result moisture under the lens which creates a fracture under the glass primary lens. 

This led is faulty and should be returned


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## SteveDavis (Dec 5, 2007)

I agree with WeLight. This does not look like the LEDs were handled/soldered/shipped properly. I'd send that back.

As for differences in Q2 and Q5, there are no visible differences with the LED off. Cree doesn't set their production line on "Q2 mode" and churn out an LED, then switch over to "Q5 mode." Cree makes LEDs and then bins them based on brightness. They have some distribution of brightnesses that they always are improving. Over time, they may change the internal structure of the package or the die layout in some way that they feel is beneficial, resulting in fewer of the lower binned parts, but that does not make it impossible to get those lower bins with the new structure, or impossible to get the higher bins in the old structure.

This is true for all LED manufacturers.


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## lewong (Dec 6, 2007)

Thanks. I understand binning and now know that there isn't a way to tell the difference by just looking at the LED.

Is there a measurement I could take with a multimeter with each LED connected to a power supply to tell the difference? I have this power supply that I used with my slot car motors. Or is an optometer or some other phtometric device (that I know nothing about) the only way to tell the difference?

TIA


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## half-watt (Dec 6, 2007)

WeLight said:


> This is an indication the leds have been out of the vacumn sealed bag for some time and were not prebaked prior to reflow, result moisture under the lens which creates a fracture under the glass primary lens.
> 
> This led is faulty and should be returned




[note: decades ago worked as a foreman in a small semiconductor factory.]

i agree with WeLight. moisture could and probably will cause premature demise of your LED, often termed "infant mortality" (death within the first 168hours of use is a general definition used for this term).

contact KD, i bet, from what i've read elsewhere, that they will send you a new one.


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## SteveDavis (Dec 6, 2007)

While LEDs can be binned based on chromaticity (the "color" of white), forward voltage at a specified current, or brightness, the Q2 and Q5 bins are both strictly brightness bins. You will need a photometer to tell the difference. It is also possible that in a darkened room, with both LEDs in the narrowest reflector or lenses you can find, at the longest throw you can manage, you'll be able to see a brightness difference in the spots.

The FC-N2-XR79-0R from fraen is an extremely efficient TIR Lens, available in single pieces from http://www.arrownac.com. Just run a search for that part number.


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## SemiMan (Dec 6, 2007)

Or you could save yourself the price of two of the lenses and shipping (and shameless advertising), and put a piece of paper over them. Make sure it is pure white paper so that color filtering does not come into play. Also make sure you run them in series to guarentee the same current and they should be run at the rated current (350mA). There should be a 20% or greater lumen difference between the two which when side by side should be pretty visible. If you reduce a single LED 20% it is hard to tell the difference, but when they are side by side, you should be able to tell. Hopefully the color is not off by much as this can throw you a bit.

Semiman


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## SteveDavis (Dec 6, 2007)

I'm here to give technical assistance and plug what we sell. I'm upfront and honest about it. I will post an answer to a tech question whether or not I get the chance to try to sell something.

We have chosen to engage CPF because we felt we could add to this community. If others feel as though I am not, I will re-evaluate how I post, or, if necessary, leave.


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## lewong (Dec 8, 2007)

As someone who is just learning about all this, I appreciate, SteveDavis' _and_ SemiMan's viewpoint. More information for me to learn - and more options - then I can decide for myself.

Thx.


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## Lite_me (Dec 14, 2007)

I just ran across this thread. I have a similar looking defect in a Q2 LED in one of my lights. It was posted in June in the LED Flashlight forum. Here is a *link.* There are pictures of the defect. 

I want to add that I still have the light. I did not return it, as it was a limited edition and there were none left to replace it with. Maybe of more importance is the fact that I carry and use this light EVERY day. Not a day goes by that its not turned on. That's been 6 months now. I just took another look at it with my jewelers loupe and it still looks the same. No change. 

Hope this info is useful.


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## stephan2148 (Dec 14, 2007)

I accidentally knocked my cree when modding (it was an older P4 I think that I had laying around). I was trying to remove the cree from a star with a lighter underneath, and accidentally touched the dome ring to produce an artifact similar to that shown. 
I did get the cree off of the star, and I thought I cracked something underneath to produce that artifact. Then it appeared to go away as I pushed on the dome, but came back as I let up. It seems like a clear silicone or gel under the dome almost. I heated the underside up again and while pressing down on the dome, the whole thing is now totally crystal clear. 
It is like I reflowed the clear goop to perfect or something.
Of course, now I have a nice dome shape burned into my finger for the next job.


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