R2 Forward Voltage Test 36 Pieces

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cmacclel

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I just received 36 R2's and tested the VF on them. Power Supply was set to 3.5v, to he right is the milliamp draw at 3.5v. This should be informative for people asking about direct drive. Each LED can be very different. As you can see below from the LED's tested that ONE specific LED can draw 4x the current as the same BIN LED from the same reel. :)

R2-vi.jpg
 
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I got around the same results, apparently there's not much consistency between LEDs from the same reel. Your LEDs actually were 1 chain of 36 emitters which I had to cut in 4 for shipping. I have 10 of these R2's myself and my readings at 350mA go from 3.22V to 3.57V.

I wonder how this comes. When the first Q5's were released there was the problem of extremely high Vf's, although Cree added a bond wire which should lower the Vf, especially at high currents. I remember the good old days when P4 was the highest flux bin, but Vf readings were very constant AND low (I remember I tested 10 P4's at 350mA going from 3.15V to 3.22V). Apparently the extra bond wire didn't help that much... I suppose there's some other change which increases the Vf?

Even though the Vf's are not very consistent on these R2's, I really love them. Compared to the P4 they give a huge brightness boost and even compared to Q5's they look brighter to the naked eye. Fortunately my light meter is back on it's way to me so I can take measurements :)

Cheers to you, Mac! And happy modding with these R2's :)
 
cmacclel said:
I just received 36 R2's and tested the VF on them. Power Supply was set to 3.5v, to he right is the milliamp draw at 3.5v. This should be informative for people asking about direct drive. Each LED can be very different. As you can see below from the LED's tested that ONE specific LED can draw 4x the current as the same BIN LED from the same reel. :)
Click to expand...


Excellent Info :thumbsup:. May I request some thing?

What would be the variation in Vf if constant current of 350mA is supplied.
 
ViReN said:
Excellent Info :thumbsup:. May I request some thing?

What would be the variation in Vf if constant current of 350mA is supplied.
Click to expand...
I don't have any test results at hand, but with Mac's LEDs the difference can be up to around .4V Just an educated guess but it will be quite accurate.
 
hi mac,
I remember you did a similar test sometime ago? Was it cree Q2? Anyway can you tell us more about your test method? How did you mount the R2? And when was the readings taken after connecting them to the power supply. I have 8 pcs from Eramus but i haven't test them yet.

I would like to see if someone could measure the output per watt regardless the vf of the led. Hopefully this will tell the difference in brightness when driven at the same power.
 
So is it better to have a lower current draw? are the outputs the same? or would they still be relative to the current draw/voltage?
 
Yapo said:
So is it better to have a lower current draw? are the outputs the same? or would they still be relative to the current draw/voltage?
Click to expand...
It's more efficient to have a lower Vf at a certain current. Example : 2 LEDs both put out 115 lumen each at 350mA. LED A has a Vf of 3.2V, this makes a total power consumption (UxI) of 1.12W and thus an efficiency of 102.68lm/W. LED B has a Vf of 3.5V, total power consumption is 1.225W and thus an efficiency of 93.87lm/W. The .3V lower Vf of LED A makes it 9.3% more efficient than LED B.

Output of these Cree XR-E's is specified at 350mA current, regardless of the voltage at that current, and is between 114 and 121 lumen.

I can maybe put my test results on line at the end of the week. I test it with a constant current source of 350mA. I push the LEDs on a black anodized big aluminum heatsink and I take a reading after the LED is connected for 10 seconds.
 
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koala said:
hi mac,
I remember you did a similar test sometime ago? Was it cree Q2? Anyway can you tell us more about your test method? How did you mount the R2? And when was the readings taken after connecting them to the power supply. I have 8 pcs from Eramus but i haven't test them yet.

I would like to see if someone could measure the output per watt regardless the vf of the led. Hopefully this will tell the difference in brightness when driven at the same power.
Click to expand...


My test method is crude and simple. The LED's are placed on a sheet of aluminum with a piece of paper underneath them to isolate the contacts. The I have 2 pointy probes that a manually touch to the LED and then look at my variable power supply to check the current draw.

Mac
 
I guess this is the price we pay for Cree's tight flux bins: the lottery of Vf being up to 10% different.
 
Erasmus said:
It's more efficient to have a lower current draw at a certain Vf. Example : 2 LEDs both put out 115 lumen each at 350mA. LED A has a Vf of 3.2V, this makes a total power consumption (UxI) of 1.12W and thus an efficiency of 102.68lm/W. LED B has a Vf of 3.5V, total power consumption is 1.225W and thus an efficiency of 93.87lm/W. The .3V lower Vf of LED A makes it 9.3% more efficient than LED B.

Output of these Cree XR-E's is specified at 350mA current, regardless of the voltage at that current, and is between 114 and 121 lumen.

I can maybe put my test results on line at the end of the week. I test it with a constant current source of 350mA. I push the LEDs on a black anodized big aluminum heatsink and I take a reading after the LED is connected for 10 seconds.
Click to expand...
are you sure it is the opposite of that, instead of having a lower current draw at a Vf... have a lower Vf at a set current draw. A lower current draw probably equates to lower output while a lower voltage at a specified current draw points to more efficient I would think.
 
saabluster said:
Great post! The pictures really help you see what going on with these as far as the dispersion of VF. Thank you. Seems like this should have been posted in the "LEDS" forum.:shrug:
Click to expand...


Thats the forum I was looking for when I posted :) I missed it! I'll have it moved!

Mac
 
This is very interesting information. It makes me think that the LED manufacturers should use a much tighter binning structure but then I guess they don't really have CPF modders in mind.
 
monkeyboy said:
This is very interesting information. It makes me think that the LED manufacturers should use a much tighter binning structure but then I guess they don't really have CPF modders in mind.
Click to expand...

Luxeon and SSC do bin by Vf as well as flux.
 
During your 3.5V testing, did you feel that the lumens were the same?
 
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