# Thread: Relative Intensity vs Current?

1. ## Relative Intensity vs Current?

Hi

I have a question about output

I have been looking though data sheets for the the CREE MCE and XP-G LEDS and can't figure out the lumen output of the devices?

It must be the "Relative Intensity vs Current" graph but what does the vertical scale refer to? It's marked "Relative Luminous Flux (%)".

For example in the MC-E data sheet
If I supply the device 700mA at around 3.6V I get 190% Relative Luminous Flux. How many lumen's is that?

Thanks in advance, I have looked through the forum and couldn't find an answer so I apologize if this is a repeat question.

2. Originally Posted by cam999
For example in the MC-E data sheet
If I supply the device 700mA at around 3.6V I get 190% Relative Luminous Flux. How many lumen's is that?
Depends on which bin MCE.
Look up the binning and labeling datasheet.
Generally the binning is at 350mA.
So you might see something like 430lm at 350mA.
x 1.9 to get 700mA output.

3. Thanks znomit

I found the group codes in the "binning and labeling" document.

It sure makes a difference to the output, 220 between group F and M.

4. Originally Posted by cam999
I have been looking though data sheets for the the CREE MCE and XP-G LEDS and can't figure out the lumen output of the devices?
In addition what znomit wrote, in connection with Relative Intensity vs Current, you may want to consider the lumen droop because of the temperature rise. For MC-E, it is about 0.28% per °C rise. The reference temperature is 25°C. So, an arbitrary 75°C increase, (100°C at emitter's junction) corresponds to about 21% lumen droop in addition to that what you will get from Relative Intensity vs Current graph.

5. And to add one more twist...

The human eye does NOT respond linearly to lumens - in fact it is mostly logarithmic (like our hearing). So 200 lumens does NOT look twice as bright as 100 lumens - so don't sweat and extra few lumens here & there....

I have found http://www.icaen.uiowa.edu/~aip/Lect...ys_lecture.pdf to be an interesting read and is what I based the current tables in my various *flex drivers starting way back in 2003.

cheers,
george.

6. ## reference lumens

Now that I know what reference lumens are I thought I would look at a few different LED and see if I could make some sense of all of the numbers.

The MCE chips looks like the best value due to the high reference of the M Bin, 430 lm.

these are the figures
MCE
binning range 210-430lm at reference 350mA. At 700 mA 357 to 731 lm
Power used at 700ma*3.5=2.4W

XPE
binning range 93-122lm at reference 350mA. At 1000ma 223-292lm
Power used at 1000mA*3.5=3.5W

XPG
binning range 114-139lm at reference 350ma At 1000ma 285-347lm. Yes I know it runs at 1.5 A but I thought a referance at 1A would be in line the the others. I don't feel like getting a 1.5A capable battery pack either.
Power used at 1000mA*3.3=3.3W

It's late I hope the post makes sense!!

7. Originally Posted by cam999
Now that I know what reference lumens are I thought I would look at a few different LED and see if I could make some sense of all of the numbers.

The MCE chips looks like the best value due to the high reference of the M Bin, 430 lm.

these are the figures
MCE
binning range 210-430lm at reference 350mA. At 700 mA 357 to 731 lm
Power used at 700ma*3.5=2.4W

XPE
binning range 93-122lm at reference 350mA. At 1000ma 223-292lm
Power used at 1000mA*3.5=3.5W

XPG
binning range 114-139lm at reference 350ma At 1000ma 285-347lm. Yes I know it runs at 1.5 A but I thought a referance at 1A would be in line the the others. I don't feel like getting a 1.5A capable battery pack either.
Power used at 1000mA*3.3=3.3W

It's late I hope the post makes sense!!
You need to multiply the MCE power by 4. Its essentially 4 XPEs squeezed together, the penalty is the extra heat further degrades performance. Add to that you have a bigger light source so need bigger optics.
Each of these LEDs have good points and bad points.

8. Originally Posted by cam999
MCE
binning range 210-430lm at reference 350mA. At 700 mA 357 to 731 lm
Power used at 700ma*3.5=2.4W
Yep, that looks about right for lumens. Znomit's right about the power issue so about 10 watts. On the other hand I have no idea what to expect for a junction temp when used in the real world. I suppose it depends on your heat sinking and the ambient air temp/cooling effect of the moving air. According to the graph if you can keep it under 70 degrees C. you will only have a 10% loss in Lumen output (658lm) which shouldn't be that noticeable. Then there are optic losses. Maybe another 10-20% depending on what you use..??
IMO the optic choice is one of the biggest issues when building a light ( size and heat sink being foremost ) If you can't put the majority of the light where you want it you are dealing with major lumen losses.

9. Originally Posted by znomit
You need to multiply the MCE power by 4. Its essentially 4 XPEs squeezed together, the penalty is the extra heat further degrades performance. Add to that you have a bigger light source so need bigger optics.
Each of these LEDs have good points and bad points.
MCE being 4 XPE together makes more sense of the lumen figures.

On the cutter site it has the Ledil optics for the MCE which are very small being 21.6 square and 13.1 mm deep.
Which I was thinking of using, it being easier (hopefully) to get a square enclosure rather than a circular or oval one.

Looks like I will be needing some extra heat sinking.

Which prompts a question, what does thermal runaway look like? It doesn't seem to get a mention in the forum, which surprises me.

Diminished output is what the graphs in the spec sheet say but does this cause irreversible damage, black smoke escaping sort of thing. Or after it has cooled down it's OK again.

10. Originally Posted by cam999
On the cutter site it has the Ledil optics for the MCE which are very small being 21.6 square and 13.1 mm deep.
Which I was thinking of using, it being easier (hopefully) to get a square enclosure rather than a circular or oval one.
I used the square Ledil CMC SS optic on my first MC-E light with somewhat disappointing results. Even as a bar light I feel it is too floody of a beam. Later MC-E builds were with the Fraen narrow reflector. IMO an excellent beam from that, though some find it too tight.

Originally Posted by cam999
Looks like I will be needing some extra heat sinking.
Design around 2 square inches of surface area per watt of LED and you will be fine for a bike light. It will get hot if left on high when stopped, but runs cool enough with minimal airflow. Ambient temps will have some effect on that.

Originally Posted by cam999
Which prompts a question, what does thermal runaway look like? It doesn't seem to get a mention in the forum, which surprises me.
Probably because it hasn't happened to many of the posters here. I've never seen it in a high power LED.

Originally Posted by cam999
Diminished output is what the graphs in the spec sheet say but does this cause irreversible damage, black smoke escaping sort of thing. Or after it has cooled down it's OK again.
High temps will shorten the life of the emitter. How much worry is that? A 10k hour life versus 20k hours is kind of pointless for a bike light. How hot does it take to cut the life in half? I don't recall seeing any data on that though it must exist.

11. So for a single MCE I multiply my 2.4 Watt by 4 gives me 9.6 Watts

2 square inches per watt makes 19.2 Square inches or 480 mm square roughly.

I think I will be switching to low power or off if I stop, considering I don't get the snow I see in some of the beam shots. Good to know thermal problems aren't common though.

Thanks for all the info

12. Cam, are you building a bar light or is this for helmet mounting? Just wondering...

13. I was trying for a helmet light, but if things start to get big and heavy it might become bar mount.

I thought the Ledil lenses looked good for a helmet mount light being compact.

14. Originally Posted by cam999
I thought the Ledil lenses looked good for a helmet mount light being compact.
While the Ledil CMC optics for the MC-E are fairly small, be sure you will be satisfied with the beam quality. For a helmet light most users prefer a pretty tight beam that throws light a good distance. You will not get that with the Ledil CMC. The Ledil Iris has been shown to make a good beam and the previously mentioned Fraen narrow reflector has an excellent beam for helmet use. If the 21.6mm square form was your target for a housing design I would consider putting 4 10mm square XP-Es with the carclo 10417 optics in the same size housing. You'll get more light and a better beam.

15. ## LED and heat

Hi all great-minds-of-light, :-)

Could anyone drop some clues regarding "why does heat reduce light emission intensity" in this case?
Does this has anything to do with the notorious "change in conductivity with a heated semi-conductor"?

Thanks

16. Originally Posted by cam999
I was trying for a helmet light, but if things start to get big and heavy it might become bar mount.

I thought the Ledil lenses looked good for a helmet mount light being compact.
Okay, then I have to agree with what Vancbiker just wrote. You would probably get a better beam pattern with a reflector vs. an optic if looking for a helmet light. I have an MCE torch that uses a 37mm reflector and it provides an excellent beam pattern, however most people would not like the size. Then there's the problem of projecting the "4-die-cross-hair-pattern". This happens when using something that narrows the beam. My torch has this same issue but it is minor ( in this case) and is not very noticeable on the trail.

Another option you might consider for helmet use is building with a SST-50 LED. It uses only one large die and at 2.8-3A should put out as much light ( or more ) as an MC-E M-bin BUT without the *cross hair pattern of the MC-E. ( *Now with a bar light using a wider optic this wouldn't be a problem. )

I have a torch that uses a SST-50 and it too makes a very nifty helmet light. I can't wait till someone decides to do a helmet build with one of these. In my opinion though, reflectors look to provide the narrowest beam patterns when it comes to the larger die power leds.

17. VancBiker suggested the Carlco 10417, which is an optic rather than a reflector according to the cutter site, so is this OK because VancBiker and Cat-man-do were of the opinion a reflector would be a better choice?

I came across Toaster79 setup over in the “post your ugly but functional” thread, and thought that would make a good helmet light...

XPG looks like the one to use so I went to cutter to have a look

This is the part number

XPGWHT-L1-1BO-R5-0-01

Most of which I have de-coded except

1B0 I couldn’t find the “0” the rest is Chromaticity or dominate wavelength group on page 5 of the Binning document gives the region and a set of x and y figures that I assume are the axis of the graph on page 9 meaning the temperature is just below 6500K between overcast sky and Sun at noon as a temperature.

The next “0” after the “-“should be the forward voltage group. Letters are between B and F in the binning document on page 8. Safe to assume below 3.75V for each LED ? That’s the highest figure in the document, seems to only list coloured LEDS as well. Forward voltage seems a really important figure to be missing. My current battery pack, I had lying around has an output of 7.2V.

http://www.cutter.com.au/proddetail.php?prod=cut937

“XPG on a metal core PCB”

can’t find the code anywhere is it a Cutter custom code?

I will take a suggestion on a driver board.

I know now why there are a lot of threads starting with “could someone suggest a setup”.

Thanks for all the responses, I don't know how anyone could work this out on their own.

18. Originally Posted by cam999
VancBiker suggested the Carlco 10417, which is an optic rather than a reflector according to the cutter site, so is this OK because VancBiker and Cat-man-do were of the opinion a reflector would be a better choice?
The Carclo 10417 optics are used with the XP family of leds. The reflectors I mentioned earlier are for the MC-E led.

I was throwing out alternatives to the MC-E with Ledil CMC optic combo when I referred to the quad 10mm XP-E and 10417 combo. I hope I was not creating some confusion.

If you have settled in on the XP-G led, your next decision is housing shape and size. That will narrow down your optic choices. For example, I prefer a small helmet light with a low profile.

Micro helmet light

The 10mm led and 10417 optic in a flat, double, triple or quad, layout fits that requirement nicely. Beam quality is not the best, but certainly usable. If you like other form factors, your choice of optics widens.

If only someone would build a 10 mm narrow reflector for the XP led family. I thinking about trying that after I get my current car project done.

Choose either R5 bin XP-G. I'd be surprised if you could really see enough difference in them to matter. Pick the style of MCPCB that most closely matches your optic selection. Consider buying an extra led and for sure a couple extra optics. It is not uncommon to spoil a component or two during the build, especially if soldering and assembly are not real familiar to you.

You'll need to decide how many XP-Gs you are going to use for anyone here to offer advice on a driver and wiring scheme.

19. Thats a very impressive compact head lamp you have there VancBiker.

Is there any disadvantage in mounting the buckpuck away from the LED except needing an extra capacitor, the 3021/3 spec sheet suggests a cap if the power source is greater than 18 inches away.

I was thinking of the XPG in a double or triple unit with a Carclo optic with both a tight 10417 and medium 10413 optic.

How do I "Pick the style of MCPCB that most closely matches your optic selection"?
Is there another spec sheet I need to look up to find out what a Cutter XPG10SSQ means

it's here beside "XPG on Metal Core PCB"
http://www.cutter.com.au/search.php?...e=&scat=&sman=

I was thinking of using the bFlexUIB2 controller it having a lot of features built in, stat LED etc

20. Originally Posted by cam999
Is there any disadvantage in mounting the buckpuck away from the LED except needing an extra capacitor, the 3021/3 spec sheet suggests a cap if the power source is greater than 18 inches away.
No disadvantage at all. Many other lights have been built with the puck in the head. I mounted it with the battery just to keep the head small.

Originally Posted by cam999
I was thinking of the XPG in a double or triple unit with a Carclo optic with both a tight 10417 and medium 10413 optic.
I doubt that you will want the 10413 medium in anything for an XP-G bike light. The 10417 is plenty wide, even for bar use. Optics are cheap so buy an assortment. Build a housing that allows you to change them easily and experiment. That's part of the fun of DIY.

Originally Posted by cam999
How do I "Pick the style of MCPCB that most closely matches your optic selection"? Is there another spec sheet I need to look up to find out what a Cutter XPG10SSQ means
Here is a page showing the different MCPCB styles.

http://www.cutter.com.au/proddetail.php?prod=cut937

Originally Posted by cam999
I was thinking of using the bFlexUIB2 controller it having a lot of features built in, stat LED etc
The flex family of drivers are my favorite. They are an excellent product. Some are put off by the "programming" required, but it is really quite simple. The temp sensing and battery monitoring features work very well. They allow you have a DIY light with better features than many commercial lights.

21. thanks for the URL, certainly makes easier with everything listed together and a picture.

Definitely going to buy a few optics and give them a try, they are pretty cheap after all.

I was going to fix the leds and optics to a big old heat sink I have and run them from a bench power supply to see how they worked before mounting. Then maybe move to a diecast box before venturing into the custom enclosure building challenge.

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