11-12-2006
This great topic was started by cmacclel of CPF. It was a discussion about the MCPCB that ETGTech used to mount the CREE XR-E LED upon (not a CREE solution). This led me to do some testing and further dissection/evaluation of things.
CPF-cmacclel
Many have you have been asking about the thermal conductivity of the Cree round and star bases so here are your pics.
As you can see there is a thin layer of PCB between the thermal pad of the Cree and the actual aluminum heatsink base. Not a very efficient solution in my opinion. Lumileds emitters are directly thermal epoxied directly to the aluminum for you would think a much better thermal path.
FYI, those stars and rounds are *NOT* produced by CREE, but by other companies, and some distributors. The ETGTech version is a very common one. Unfortunately, it is lacking.
All MCPCBs are most definitely not created equal, and I most definitely applaud your taking one apart to show us all the short comings of the first round of MCPCBs produced by various third parties for the CREE LED. You get what you pay for.
They buy the CREE LEDs and mount them on the boards themselves.
(also of note, if the LEDs are not kept below 30% humidity or lower, this can lead to color variations after reflow soldering operations. This is well known amongst folks that work with white LEDs, but not that well known amongst board assembly houses. Make sure your board assembly houses know this!)
The FR-4 you see there is a great insulator (epoxy and fiberglass), and it has to be made extremely thin just to get modest thermal transfer.
FR-4 and Fiberglass
Thermal conductivity 0.03 to 0.04 W/mK (thermal insulator)
Wakefield 120 Thermal Grease:
Thermal conductivity 0.735 W/mK
Titanium Alloy Ti6Al4V:
Thermal conductivity 6.7 W/mK
Aluminum:
Thermal conductivity 190 W/mK
Copper:
Thermal conductivity 386 W/mK
(higher W/mK means it transfers heat better)
An example of the problems this causes is shown here:
Directly soldered to copper, for comparison:
[cpf-cmacclel]
So Newbie what boards be it round or star provides the best thermal transfer?
Mac
Well, that is a tough one to call. They do function, but why would these distributors purposefully throw the cat in with the wash?
Here we have a really nice XR-E product that CREE worked so hard at minimizing thermal resistance, so you could pull the heat out of the die, in order to maximize the light output (lumen output drops as the LED heats up), then some distributor comes up with a cheap hack that works the opposite way, and launches them off to yet another board house for mounting. I don't know what nutcase designed these things.
(likely someone that was trying to maximize profit margins)
They could have very easily put 150 copper vias under the thermal pad area, which would have given direct thermal transfer through the board directly to the aluminum (common in RF designs), and also flooded the copper from the thermal pad across the surface of the board, to also act as a heat spreader. This would have resulted in a thermal resistance well under 0.5 C/W. Instead of using what looks to be 0.000707" thick copper (1/2 oz.), they could have easily used 4 oz copper to help maximize the spreading across the entire surface of the board. Sure, so it would have actually cost nothing for the vias as well as nothing for the copper flood. If they were wanting to maximize performance, they could have spent another 0.04 dollars for the thick copper, it sure would have helped further. I don't know, but this just reeks of cheap.
If I'd spend some of my own hard earned cash on these myself, you bet I'd be on the phone and someone's ears would be on fire...this isn't rocket science, just Thermal Management 098.
It would be cool if CREE were to take the mess these distributors made out of these and make something proper. Though, I don't think there are any plans for this- but I've never asked CREE about it.
Which works better? Harumpf, neither?
In reality, if you don't care much for getting great performance, and don't mind loosing some of your lumens due to die temperature rise, as well as color shift due to higher temps, I guess they work adequately.
[CPF-chesterqw]
maybe there is some super secret formula for a thermal conductive pcb?
Not really, the techniques have been pretty common for the past decade, nothing new to see here. Usually, where the FR-4 is used in the ones ETGTech supplies, you use instead, a thermally conductive dielectric material, instead of an insulator material.
I'm looking at one of these and the FR-4 layer they use looks to be about 12 mils thick, but I do not have one that is unmounted for measurement. If this is in fact correct, the thermal resistance would be about 25 C/W.
Typical MCPCB's from way back when used to use 3 mil thick FR-4, which results in a thermal resistance of about 7 C/W.
Something that came out a few years ago, was a special thermal dielectric material that enhanced the thermal conductivity of the dielectric layer (typically the board material was black in color inside), which has a 3 C/W thermal resistance.
Just simply using 150 vias (which is 100% free in volume manufacturing) under the part can lower the thermal resistance to way below 0.5 C/W. This can be lowered even further by utilizing top and bottom copper layers, flooding from the thermal pad (the copper spot you solder to) across the board surface.
Using vias as thermal transfer points can be quite effective. You could make the board 39 mils thick (1mm), and do nothing more than put only 9 vias of 0.5mm in diameter, and still end up with a thermal resistance of 9 C/W. If you reduce the board thickness to one of the standard pre-preg board materials, like the 3 mil thick material (0.0762 mm), you end up with a thermal resistance of only 0.69 C/W.
Keep in mind, with the CREE, the ceramic material used is not the best for thermal spreading. As such, one would most definitely want to put the vias right under the die area.
So, how does it work in the overall scheme? I took a A19 head with a 2x123 cell body, and with the surface area, very roughly estimate the flashlight has a 30C/W thermal resistance to the ambient air. Using the 12 mil thick FR-4 MCPCB would end up nearly doubling the thermal resistance of the overall solution from the LED die to the ambient air.
However, if one were to carry the flashlight in their hand, as most people do, you always sweat a little, causing a very good thermal path from the hand, to the blood steam, which then pumps the heat away, much like a coolant system does for the engine in a car. Unfortunately, I do not know the exact C/W of this interface, but in this case, the use of the ETGTech MCPCB would be by and far be the highest thermal resistance point, and have a highly significant impact on the overall thermals.
On another note, if you want to go high tech instead:
There have been some developments in the past few years where they use graphite as a thermal spreader (done right, it has a lower spreading thermal resistance than even copper, about 20% better), then use the area advantage to lower thermal transfer through the board.
Examples of some of these newer technologies:
http://www.graftechaet.com/Technica...G-ZS-PP-098.pdf
http://www.irctt.com/anotherm/index.aspx
[CPF-SemiMan]
As NEWBIE has pointed out, there are vast differences between MCPCB materials. The best in my experience is LAIRD THERMAGON 4mil thermal pre-preg with 2ounce copper. I have only used it on an Aluminum core, but I hear it is even better on a copper core. It is not as good as mounting directly to copper, but it is probably as close as you are going to come with current products where you need isolation. It appears to be as almost if not as good as some of the esoteric methods such as Anotherm where they place traces right on the heat sink. The material is 0.053C in2/W so for a 5mm*5mm conduction path, you can get about 1.3C/W. With some extra copper for spreading you can get this down to about 1/2 of that.
As Newbie has pointed out though, using lots of vias, especially if they are filled, will be even better. However, if you need isolation, the Thermagon is one of the best options.
Semiman
[CPF-cmacclel]
Last night I did a quick test with the MCPCB's I ran the mounted cree for about 1 minute while measuring the LED die temp then the back of the MCPCB the difference in temp was only 15 degrees so they seem like they are working ok.
Mac
Good deal.
How did you go about measuring the die temperature on yours?
I hope it wasn't an IR thermometer, they are not that accurate in this situation.
I'm seeing 10-20C rise just from the aluminum of the MCPCB to the body of the CREE, which means the die is even much hotter than that.
[CPF-cmacclel]
Yup it was an IR thermometer
Hey I tried
Mac
[CPF-chimo]
Here's another reason not to buy a mounted emitter. This is a 1W Cree emitter from an earlier group buy (It is NOT an XR-E). It is mounted on an ETG heatsink. I removed the emitter from the board today. That little dab of solder is certainly not the best method for transferring heat!
Paul
cmacclel
Yup it was an IR thermometer
Hey I tried
Mac
Well, hey, thanks a bunch for trying! Any effort to learn, study, or explain is a good one!
If you go up a few posts, up to my IR pictures, you will note the one that is on the ETGTech MCPCB. Note that the hotspots on the LED body are about 13C above the top surface of the MCPCB temperature. So for surface temp, it basically agrees nicely with the IR camera. And we still need to transfer the heat through the MCPCB to the aluminum on the back side. Also notice, how you see the surface temperature of the lens, and not the die, you can't even make it out...
In reference to chimo's picture of the ETGTech MCPCB above...
I've seen some really piss poor soldering in my days, but dang ETGTech did a really poor job on those.
Definitely click on the picture link, it tells a thousand words...
Outstanding find chimo!
[CPF-45/70]
... if NASA/JPL oversaw the reflow process and it was perfect, these MCPCB's still wouldn't be worth a crap anyway. Just trying to find a solution.
Dave
[CPF-McGizmo]
I am not sure why these MCPCB's aren't worth crap but like you, I too need a solution. My present one is using these MCPCB's.
So far, they seem to work fine so I am really feeling stupid here!
According to ETG and a spec sheet they provided me, the isolation layer used on the MCPCB's is rated at less than .6 C/W resistance. Now the whole LED package is bonded to the MCPCB with this isolation layer and this means that the area under the LED lead pads as well have this thermal connection. From messing with these LED's, it is clear to me that this LED package has great heat transfer throughout and this includes the lead "wings";. I like the idea of the center pad and the two lead pads all solder flowed to copper which then has this isolation barrier of reasonable thermal resistance and then on to the core of the MCPCB. In a more perfect world, the MCPCB would be silver and the center portion would be somehow raised up directly to the plane of the center pad of the LED and only the lead pads would have an electrical isolation layer and perhaps only the positive pad for that matter. Well If such a board is available or any board with marked improvement over the ETG board, sign me up.
In the mean time, I will stick with the crap I have available and the crap that seems to work pretty well to me.
Well, something is quite wrong with their spec, to say the least, unless you are driving the A19 at 20 Watts?
It is extremely clear the package does not have good thermal spreading in it, and something is wrong with the ETGTech board.(I checked this one below, and it had solder properly flowed, yet it's performance was still lacking)
Possibly their process is partially to blame. I took Chimo's picture of the ETGTech MCPCB and blew it up, to look at things closer. Notice how the solder didn't flow, as well as the grain of the CREE surface in the solder area:
McGizmo
According to ETG and a spec sheet they provided me, the isolation layer used on the MCPCB's is rated at less than .6 C/W resistance.
Their numbers do not add up.
Even if the FR-4 was only 3 mils thick, it would have a thermal resistance of 7.4 C/W, as measured by Flomerics and OSRAM.
To work out, ETGTech's FR-4 layer would have to be 0.00025" thick.
It is not.
For a sanity check take another look at the photos, and note the temperature scale on the side for various points, like the LED near the metal ring, towards the ends, and then look a surface of MCPCB area.
Next, take a look at this one, note the scale for temperatures on the side, and compare the LED metal ring, the various areas of the flat spot on the CREE body, and then also the copper surface that the XR-E is mounted to:
I'm looking at the blown up version of Chimo's photo of the ETGTech's MCPCB again, and I'm wondering if the solder was even reflowed at all in the center of the CREE thermal pad. It could be just as likely that Chimo melted the solder under the thermal pad, and it never even got reflowed there in the first place:
Even a thick, I think it was 39.3701 mils (1mm) FR-4 board in their example, glued to aluminum, with only 9 vias in it has a thermal resistance of 9.7C/W. If one reduces the thickness of the board to a standard pre-peg FR-4 thickness of 3 mils, AND keeps the same nine thermal vias, the thermal resistance drops to 0.746 C/W. There is a tremendous reduction of thermal resistance, just by adding vias to nothing more than standard FR-4. A person can easily decrease the thermal resistance further, by utilizing smaller vias, and more of them, to increase the copper area that goes through the board. This doesn't count solder that partially fills the vias, which lowers if further. I'd seriously consider putting the vias under the LED die area and filling the whole thermal pad area with them.
http://www.flomerics.de/Produkte/Os..._Dragon_LED.pdf
McGizmo
Newbie's IR image here is contrary to what one would expect from the MCPCB. A similar image may be contrary to what one would expect from another solution that looked good in print.
This image is of a hand assembled part that does not have a good and complete thermal path from MCPCB to can (view the delta from LED to the perimeter which I believe is the can lip which is above the contact plane). The LED is being driven beyond spec. This is a sample of one. It looks like a 10C difference and this is with a drive current of 825 mA or about 3 watts? Does that mean we are looking at a delta of about 3C/Watt from source across the MCPCB itself (including not only the boundaries from LED pad through the isolator film to Al core but spread through the core and then back up through the boundary layer and into the white paint of film that is the surface finish on the MCPCB and actually being photographed)? Some of these thermal epoxies have a great thermal conductivity when used in very thin films but those numbers are also based on surface area. What do we get with a real IR photo like this when the part is mounted on a sink?
The image also agrees with thermocouple measurements, when utilizing fine 42 gauge K-type thermocouples.
It isn't much of an issue, once the heat gets to the aluminum of the MCPCB, it is getting the heat there in the first place, that is an issue!
McGizmo
I won't pretend that this thermal image is an image I can understand or properly interpret. Had Newbie scrapped a spot on the MCPCB to show the raw Al core of the MCPCB, would we see this as a hot spot in the image?
Unfortunately no.
Remember, the ETGTech MCPCB does not have the PCB portion of it covering the Aluminum core all the way to the edge, so you are actually seeing the Aluminum substrate with the highly emissive coating I put on it, at the edges.
If you look carefully in the IR picture, you can see the threaded hole portion.
Here is one of the module types I used in the photo, note a number of areas where it is bare aluminum:
(The picture below is up side down, rotate around 180)
McGizmo
What is with the streak from right to left that shows a much cooler section across the whole image? I assume I am to disregard this portion of the image but why disregard this but accept the balance and pretend to understand what I am seeing? Just what am I seeing here? How am I to read this?
This "streak" is one of the wires I installed on the module, blocking the image in that area, for monitoring things.
McGizmo
GlowBug has done a number of IR images of complete flashlights and I recall one he did of a chrome Aleph that was just bunk. It seems that chrome is not a reasonable surface to get an IR image from. The chrome seems to hide the IR energy from the camera.
No, chrome doesn't really hide the IR energy, it just is a very poor radiator of heat, and thus you cannot see it. Most shinny looking metals are quite poor thermal radiators, but something as simple as Hard Anodize is many times more emissive. A very interesting thing is that you can take aluminum or titanium, and sandblast it, etch it, and scratch it all up, and in the 7-14um spectrum, it looks like a perfect mirror, as it also reflects heat. It is one of the reasons that aluminized mylar works great both for keeping heat in, and also reflecting the heat in the summer, and the properties are often taken advantage of in fire fighting suits and "space blankets".
That is why I coat items with a high emissivity material-this makes them emit all the same.
If all the surfaces were the same, one could simply adjust the thermal emissivity settings for many shots, but it still doesn't work well with bare metals (especially since they give you reflections of ambient sources). Heatsinks that are designed to radiate are even anodized black, to radically raise the emissivity (which can raise the emissivity by 30x, and in another test I did, allowed a flashlight sized object to radiate an entire 1.2 Watts of heat, causing a large reduction in temperatures), and allow a substantial amount of heat to be released into the air/space as IR radiation.
McGizmo
Newbie has stated that he coated the part with some material that will provide the same emissivity (sp) to the camera. This makes me think that the camera is imaging the surface and not the core beneath. Isn't the core beneath insulated by both the isolation layer as well as some top film? If yes, perhaps this insulation is not significant.
Actually, the material conducts heat better than Arctic Alumina, is very thin, and is not even close to being significant.
As I've mentioned before, I also had very fine gauge thermocouples on the surfaces, which was used to correlate with what the camera reads. I use fine gauge (42 ga) thermocouples, as the heat that travels down the thermocouples wires can cause the thermocouple junction to cool, giving an error in measurements.
McGizmo
I have learned from personal experience that an IR thermometer is not to be trusted for absolute temperature readings. However, an IR image is? I can imagine that an IR image is viable for relative comparison but for absolute measure I need some coaxing.
I certainly can understand why folks often have issues with IR temperature measurement systems. Having worked for FLIR Systems, I worked with the IR camera systems on a daily basis for a number of years. I also understand some of the gotchas, and how they actually work, better than many folks.
That is why I used the highly emissive coating, and had the thermocouple wire going down to the surface, to allow me to measure the actual temperatures present while the IR pictures were being taken. I'd also taken a number of other temperature measurements on various surfaces.
If you have your emissivity dialed in properly, the system used is accurate to +/- 2 degrees C, and the delta temperatures are accurate to 0.08 degrees C.
Remember, I actually worked for FLIR Systems (a world leader in IR imaging systems) for a number of years, and also worked on the AN/AAS-33 Detecting and Ranging System (FLIR imaging based) weapons systems when I was in the military for the A6-E TRAM (Target Recognition and Attack Multisensor) Intruder, so I know a little more than your average joe about IR, and have many years of actual on hands IR experience (since 1987).
McGizmo
Thanks Newbie for the added info, insight and explanations. To isolate the effect of the MCPCB, would a better comparison be one where such a MCPCB were secured to a similar plate of copper as the discrete LED and then images made of both LED's driven at the same current (assuming the LED's are close in flux bin)?
Of course, maybe even with both LEDs wired in series, on the same plate, so they get exactly the same current, and are working against the same plate temperature.
(Since it applies directly, I'll post an image here from later in the thread, of three parts that were wired in series, so they get exactly the same current-you can see the series wires even):
McGizmo
When you say the image agrees with the thermocouples, were the thermacouples measuring the coated surface of the MCPCB or the core itself? I think you are saying that the difference is not that great anyway. I am still confused here (no doubt obvious). If the laminate surface of the MCPCB is essentially the same temp as the core then the resistance through this laminate must not be too great?!?
Large error in thinking there. Around the part, on the surface of the MCPCB...think about the amount of heat being transferred through the board. The thermal resistance of the board low enough to replace what is lost to thermal radiation. There is no actual thermal "load" on it. Kind of like a battery. Take a CR2032 battery and measure the voltage unloaded. Then put a 300mA load on the battery and you will see the voltage drop. Or even a CR123 cell, which is ~3.2V open circuit, then put a 1.5A load on it and watch the cell voltage drop to 2.7V or lower. The voltage is still present inside the cell in both cases, but the internal resistance of the cell, under load, causes the voltage at the terminals to drop. Now go back and look at the temperature of the CREE body vs. the MCPCB, as well as the direct mounted ones vs. MCPCB mounted ones.
McGizmo
If the MCPCB itself were thermally relieved in a better manner (I.E. bonded to a hunk of copper) then I believe the steady state temp would be lower than is seen in the example. With a lower steady state, would the delta be as great?
Actually, the delta would increase.
(See the picture above of the three mounting methods showing this)
McGizmo
Coming from another angle, if a LED were to be thermally epoxied to an Al sink the same size as the MCPCB and then compared to the MCPCB with FLIR imaging of both driven at the same current, wouldn't this be a better means of viewing the effect of the MCPCB's composition and thermal relief? Better yet, put a thermacouple on the underside edge of both samples and the hotter unit is the more efficient?
No, there is no thermal loading, see my comment/example a few back.
McGizmo
Perhaps you are better at identifying the differences in a basket of mixed fruit than the casual reader?
When I have items in hand, it will be very easy to sort out the fruit, to make it easier to do a direct comparison between the bananas.
[CPF-McGizmo quoting me]
In reality, if you don't care much for getting great performance, and don't mind loosing some of your lumens due to die temperature rise, as well as color shift due to higher temps, I guess they work adequately.
In your A19 flashlight, the hottest spot I've been able to find, as close as I could get the thermocouple to the backside of the XR-E, was 84 degrees C after 30 minutes, at the package edge basically, by the board. BUT, I can't get to the backside under the die, but for this exercise, we will use the 84C. You have roughly 3W going to the Emitter. We know the spec for the LED is 8 C/W. Ambient temperatures were 25C. 3W * 8 C/W = 24C. So, the die temperature would be roughly, 84 C + 24 C = 108 C.
From the XR-E datasheet, the maximum die temperature is 145C, so you are good to go, as far as exceeding the specs, and if it was 50C outside, the die temperature would only rise to 133C, so you'd be okay too. You'd loose 30% of your lumen output vs. a die temperature of 25C, but you'd be just fine.
More robust, or lower thermal resistance in your path could buy one 10% more lumens- that is all I was trying to point out earlier.
More aggressiveness in the overall system thermal path to the flashlight body could buy one further gains in the lumen area, as well as using more efficient converters to reduce overall system temperatures- to get even further lumen gains.
Of course, there is another larger monkey to chase down, the reflector coating itself, which is typically in the ~20% loss range, but may be a little less for loss contribution with the CREE XR-E, as typically, more of the CREE XR-E lumens (percentage) don't hit the reflector, as compared to a Luxeon/Seoul in the same reflector. (Sapphire Lenses pose another 15-25% losses monkey to clobber(or glass lenses, and using AR coating to clobber the monkey)
Now, if the ETGTech MCPCB, had some of the CREE XR-E LEDs that were not soldered on them properly, the situation could be much worse...kind of like what Chimo showed in his pictures of the ETGTech MCPCB.
[CPF-McGizmo]
Newbie,
Thanks for pulling this back into the perspective of the overall picture. Realistically, I think all of the lights we currently have as well as lights we will make or acquire in the future will have losses in efficiency all along the train of energy conversion from stored electrical potential to photons delivered on target. These losses will add up to a percentage we wish weren't the case and this difference will continue to be a tool of marketing where some will cite the potential and others the reality.
As an exercise in theory, application of theory and in the pursuit of design goals and execution of the design in actual construction, an awareness and understanding of the nature of these losses and feasible attempts to minimize these losses should be pursued. This is my opinion but I expect it is shared by most.
There is a gap between ideal and realistic. This gap can be narrowed if not bridged by identifying its nature and understanding its dynamics and the parameters within one's control. Threads such as these are very illumination and instructive towards such a goal.
I dare say even a poorly designed flashlight is more efficient in energy conversion than we are efficient in using our brains, to their full potential. Whether by intent or not, there is always room for improvement. You just have to find that room and be willing to pay for it.
That was exactly my whole point in sharing this information with everyone, so they'd get a better feeling for the nature of things, and people who design things can think of better ways to address the issues- without driving costs up.
Okay, we mentioned thermal vias.
So, what is the effect of a thermal via?
Lets say we take a very low cost standard FR-4 prepeg material, to keep the prices down.
Lets use 100 13 mil vias, with 2 oz. copper plating.
Punching in 13 mil diameter vias, putting in 2 oz (and remembering to change the copper from mils to oz.) and 3 mil thick board, you get:
2.16 C/W for one single via.
Online calculator for this is found here:
http://circuitcalculator.com/wordpr...via-calculator/
Since we are using vias in parallel (using more than one in the board), you then just take the C/W for one via by number of vias, to get to C/W:
2.16 / 100 = 0.022 C/W
So, it gets pretty easy and very low cost, using commonly available practices, to get the C/W down to incredibly low numbers.
If you use fewer vias, placing the vias directly under the die area will typically benefit you the most.
Keep in mind, I did not include the additional C/W reduction of any solder that is inside the via barrel, nor the further reduction due to the FR-4.
The additional nice thing about the CREE XR-E, is that it's thermal pad is electrically isolated (thank you!), so there are no worries there.
[CPF-Doug S]
Speaking of vias, in the XR-E package itself, is the thermal conduction from the die pedistal to the backside of the package entirely through the ceramic material or does the ceramic material contain hidden thermal vias?
Entirely through the Alumina Ceramic. Note I didn't say Aluminum Nitride ceramic, Boron Nitride ceramic, nor Beryllium ceramic. Yes, thermal spreading resistance comes into play..
Also of note, the ESD diode is SiC.
No hidden thermal vias in the XR-E, just the ones on the corner, for the electrical contacts.
The magnification effect of the lens used on the CREE makes it look much bigger than it really is.
BTW, it is great to see you again Doug S.
IsaacHayes
You misunderstood me. The bottom of the cree I had looked like it had holes underneath the thermal pad... (center pad)
It doesn't. Those don't go through to the other side, and they are actually squares.
With the right lighting and magnification, one can see the ceramic surface through the holes.
Sorry about poor picture quality.
[CPF-Anglepoise]
I have treated mine just like a LUXIII.
I sanded the bottom absolutely flat (exposed smooth copper ) and then did the same thing to the bulkhead. Then a thin layer of AA and glue together under spring pressure till set.
Then I grind the edges to disconnect the bottom electrical connections and solder to the top pads.
Now I have no way of measuring and comparing analytically, but my feeling is that heat transfers perfectly and that this will not cause any future problems.
I feel certain that this method will move heat to the bulkhead heat sink better and more efficiently than having a poor quality MCPCB in there as well.
IMHO, the MCPCB does not help the issue at all.
[CPF-McGizmo]
Anybody who has handled these LED's or soldered to them realizes that the ceramic package of the XR-E doe a magnificent job of distributing theheat well and throughout. I believe the FLIR images also show this. SO, the perfect thing to bond a XR-E to would obviously be another XR-E!
If there were room on the Z axis, this is a perfect application for Newbie's heat pipes! I used a diamond bur to remove the trace on the top corners of the LED facing you to open the "loop" for inputs. The thermal transfer to the brass pedestal seems to be quite good!
I've been working with these CREE parts for over two years now and find the ceramic package most definitely does not do that "great" of a job for heat spreading.
In the photo below, you can very clearly see a 7 degree Celsius delta, just across the ceramic, next to the metal center, then out to the end of the ceramic pad. It is even hotter inside, under the dome- especially in the center at the die, where you cannot see (glass does not transmit IR in the 7-14um wavelength range).
Sorry, I am most definitely not going to buy into that idea, and if I did, I'd have to be quite blind and ignorant to say the least...
Then you take the same LED, and mount it to a copper slab, such that you can pull the heat out of the center, and look how the pad temperature looks much uniform:
It is the copper that is helping tremendously.
The ceramic does a decent job of transferring heat, but not excellent.
I have an old image of a CREE with the dome and ring remove, just the die on the substrate, and the poor thermal spreading becomes quite clear. I'll need to do this to an XR-E, and put pictures up. This is why it is so important to pull the heat out from the center of the die well- but the area of the whole CREE does help in theory.
Isaac-
I took some more shots of the squares in the thermal pad of the CREE, see the ceramic under them?
The square hole in the thermal pad copper:
The electrical via on the electrical connection pad:
[CPF-McGizmo}
Newbie,
In the two FILR shots where you can see the LED and its surrounds, I assumed I was seeing a rectangle that represented the whole package. It also seems that the temperature is consistent across this rectangle. In the close up you just provided, there seems to be a greater contrast in color change and the color representing 78C which before seemed outside the package and on the MCPCB is now seen to be on the package? Is this a close up of the same image or a different image?
Maybe this would help to see what I've been trying to show. Something that is obvious to me, isn't always evident to others. I've tried to "ghost" the image of the visible picture over the IR picture of the same item. Scaling isn't perfect:
>As far as soldering to the package, I see zero difference in how well they wick the heat away, as compared to the old XL7090 part.
Don,
The old XR7090 part also has a thermal resistance of 8 C/W as shown here:
http://www.cree.com/products/pdf/XLamp7090XR.pdf
The die itself is larger than the old die from the older XL7090. It is 1mm by 1mm, instead of 0.9mm by 0.9mm. This means the area of the die is increased by 1.24 times larger than the old die, which would be likely to reduce the thermal resistance. Possibly they increased the area of the SiC ESD diode that they mount the die upon, which would also help thermals.
When you solder things down, and if you only had a 5C/W difference, the temperature on the die would be 15C difference. This would work out to a 5% loss in light output. However, this die is not mounted on solid copper, and has a thermal spreading resistance. So, one could reduce the thermal spreading resistance in the system, by getting the area directly under the die area- closer coupled to the heatsink. Also, utilizing something with a very high thermal conductivity to reduce the thermal spreading resistance would help (like a thicker copper layer than 1/2 oz, or thicker than 0.0007").
As I presently understand it, the ceramic that is used is an Alumina based ceramic.
Here is a comparison chart of the thermal conductivities (higher is better) for a few metals, and the various ceramic fillers, that primarily comprise the ceramics or compressed ceramic fired forms:
[CPF-Doug S]
Jar, the pictures are great! I am, however, in the camp that is having a bit of trouble interpreting them. I have a couple of questions whose answers might be buried in this thread but I failed to see them.
1. What is the drive level for the MCPCB thermal images?
If you look back in the thread, you will see the A19 XR-E flashlight converter measured 800mA to the LED on the ETGTech MCPCB that is mounted in the A19 XR-E flashlight. (I've got two A19 GD converters, one which puts 800mA to the LED, and another that puts 945mA to the LED)
The direct copper plate soldered one is also at 800mA.(unless otherwise noted on the picture-I have a number of pictures floating around...)
[CPF-Doug S]
2. For those MCPCB thermal images is the MBPCB in turn mounted on a heatsink or is it just in free space? It would seem that the former configuration would be the one most revealing of the MCPCB performance relative to having the package mounted directly on a massive heatsink.
The A19 flashlight has an overlapping rim where the edge of the MCPCB is attached with thermal epoxy, and behind the board, they also filled the Ecan with thermal epoxy. They staked MCPCB into the Ecan by squishing the MCPCB Aluminum material edges up against the Ecan wall at sixteen points.
I have further tests underway now to learn more. On the same exact copper plate, three LEDs are wired in series, so they will each get the same exact current.
-One, direct solder to copper plate.
-One, AA thermal epoxied to copper plate, cured under heavy weight.
-One, ETGTech MCPCB AA thermal epoxied to copper plate, cured under heavy weight.
[CPF-Doug S]
3. In the thermal images is the cursor location showing the peak temperature located over a portion of the package where the coating which equalized thermal emissivity *has not* been applied?
The cursor is on the peak (85 degrees C). The peak is on a surface where +98% thermal emissivity material has been applied. Correction factors for the coated areas have been already applied. This peak temperature is on the ring, as well immediately around the copper metal lens holder at the base of the LED. As I did not want to get the emissivty material on the lens, only parts of the copper ring were coated on accident. The line across the photo is a 42 ga. thermocouple connection I made, and this wire is blocking the IR "light" and comes out towards the camera. (interesting how IR light bends around things a bit better, due to it's longer wavelengths)
See the ghosted image of the visible part overlaid upon the IR Image. Notice how abruptly the temperatures transition near the ring, and then drop on out to the edge of the electrical pad area (this is a IR image of the part mounted on the ETGTech MCPCB):
[CPF-Doug S]
4. You seem to have an almost endless supply of great Cree emitter pics! One I'd love to see if you already have it is a XR or XR-E sectioned in a vertical plane.
Thanks for sharing your great work!
I'll see if I can find the cross-sectioned device photos I have done. It was a pain, and I ended up having to use diamond to cross-section the hard ceramic.
Isaac,
As I have mentioned before, glass does not pass 7-14um wavelengths, and thus you will not see the die temperature, or an image of it. This is just one of the reasons, that attempting to use a low cost IR thermometer is nearly worthless for measuring die temperatures, and is a lesson in futility. However, you can measure the surface temperature of the dome, if you know the emissivity of the surface.
[CPF-Moat]
This is all some wonderful and interesting information, Newbie... even if I never get the opportunity to touch soldering iron to a Cree LED. Thankyou - this "nobody" lurker appreciates your efforts here, and in so many other threads over the years!!
Moat is quoting me here:
I have further tests underway now to learn more. On the same exact copper plate, three LEDs are wired in series, so they will each get the same exact current.
-One, direct solder to copper plate.
-One, AA thermal epoxied to copper plate, cured under heavy weight.
-One, ETGTech MCPCB AA thermal epoxied to copper plate, cured under heavy weight.
[CPF-Moat]
The results of this test will likely provide some very useful answers/insight for many folks here. Bravo... and looking forward to it!
[CPF-Anglepoise]
Newbie,
Look forward to see the 3 way test results.
Your hard work on this is appreciated
Below is a section of an XR-E.
What looks like a copper connection between top and bottom in the photo
is just the copper 'smearing'. Second photo is a little clearer.
There is no visible to me connection between the die and the bottom rectangular copper pad.
Here is the setup with no emissivity coating, the temperatures are *HIGHLY INACCURATE*
Here is the same setup, with a high thermal emissivity coating on all parts, so we can see the actual temperatures accurately (NOTE, TEMPERATURE SCALE ON SIDE HAS CHANGED!):
The parts that were mounted with Arctic Alumina were bonded under weight for over 12 hours.
The copper sheet metal that the parts were mounted to was placed upon another plate to help get rid of the ~9W produced.
As you can see, the Arctic Alumina Thermal Epoxy to the copper plate nearly works as well as soldering directly to the plate. The ETGTech MCPCB doesn't work nearly as well as the other two options.
The AA Thermal epoxy XR-E has a dome temperature of 42 degrees C.
The direct solder XR-E has a dome temperature of 39 degrees C.
The ETGTech MCPCB has a dome temperature of 54 degrees C.
Notice the wire going from the MCPCB to the direct copper soldered one, and how the wire is conducting heat from the MCPCB mounted XR-E, and how it fades along the wire length.
McGizmo
Newbie,
Thanks for your work and effort here. In this test set, what would you estimate the relative light output differences to be between the LED's? I can't find a graph on the XR-E in any of the data sheets I have showing the reduction in relative light output based on junction temperature. In a possibly related graph I have access to, there seems to be a 3% reduction in output per 10 degrees of C. Does that sound about right?
Using my calipers on the graph off their website datasheet, I see ~4% per 10 degrees.
Keep in mind, the case temp is only relative to the die temperature. And we cannot see the case temperature directly underneath the die. (and the die is even yet hotter)
The best thing to take away from this is to note the differing case temperature from LED to LED, and note the changes in case temperature at different points on the LED.
On the photo with the thermal emissive coating (the only accurate one), the dome hot spot is 54C. The average temp of the ceramic base is roughly 44C.
The delta here is 10C. (don't get mislead on the LED case, due to the solder pads on the MCPCB).
On the direct solder one, the dome hotspot is about 39C. The ceramic base temp is about 34C. The delta here is 5C.
Odd...the power input is nearly the same, within 2%, accounting for differing Vf and equal currents.
If you think about it a bit more, if there was no spreading thermal resistance, the deltas should have been about the same, with the same power input. But they are not. This would lead me to consider the idea that the die is even more proportionally hotter on the MCPCB mounted one, than what the LED case temperatures are showing.
The copper sheet metal temperature is about 31.5C.
When I get a chance at some point in the future, and I have plenty of extra XR-Es, I have some 42 gauge K-type thermocouples, and it might be interesting to place them directly on the dies.
With everything already mounted on the copper sheet metal (oops), soldering on the MCPCB one was immensely easier to solder on, as compared to the other two.
KWillets,
Your technique works great for amber, decent for red, okay for green, but blue die used in the white LEDs do not shift their wavelength that much with temperature. An example, for one of the Luxeon power type LEDs dies at ~15.5C the peak wavelength of the blue was 463nm, but at 82.2C it was 469nm. One would need a method of measuring rather fine shifts, as it works out to only 0.135nm per degree C. This is an entirely different matter as compared to Amber LEDs which shift all over the place (or even red LEDs in comparison). If you had a full optics lab at your disposal, one could probably accomplish this, or build up a diffraction grating/prism, some known precise spectral sources, and take advantage of distance across a room (or optics), in order to calibrate and then measure the shift. Now, if you characterized a particular lot of LEDs, you could do what Nandaren(sp) did, as the phosphor helps amplify this, when looking at the whole spectrum. One could use the CIE co-ordinates or Kelvin temperature(less accurate). You'd do a very narrow duty cycle, to minimize heating, measure that LED every 5C change in ambient temperature (after allowing the temperatures to stabilize), and build up a chart with the LED and a thermal chamber. Not all LEDs track the same though, so there would be some errors if you didn't use the same LED. One could also use the old HP method, where you look at the Vf change (they stated something like 2.8mV change per degree C, if memory serves correctly, for blue). fyi, the wavelength shift is only in the range of 0.04nm per degree C for the blue die, such that a 10C rise would only be 0.4nm of shift)
Each of these methods is a project by itself to do properly.
It isn't too hard to actually do, it just takes time and care. I'd love to read the write-up, look at the photos, and see the results- if you'd like to take that project on.
As it stands, we were just looking to see if the MCPCB works as well as direct soldering, and how well Arctic Alumina epoxy the emitter to a copper plate works, when compared to direct soldering.
Results are pretty simple, MCPCB is the worst, and direct soldering is the best, with AA epoxy being close to soldering. No surprises here.
Do not forget, that these measurements do not include heat generated by converters, heat generated by batteries, and the various thermal resistances typically found in an actual flashlights. (a good example, would be in a titanium flashlight which has over 25x higher thermal resistance than aluminum)
Anyhow, it is the next day here, and it is time to hit the sack now.
[Chimo]
Great work Newbie! I was waiting for this one. It's nice to see the comparison between the three.
You've already answered a question I had re power to each LED. They seem to be fairly closely matched (2%). The heat flow on the interconnect wire is quite telling as well.
On the MCPCB, is there any thermal compound between it and the copper sheet?
BTW, thanks for doing this.
Paul
[CPF-Kinnza]
Good Job
Newbie!
Yes, result are how previously expected, but it measures accurately the differences, so each one can decide the best way to mount the XR-Es, as the thermal behavior is opposite to mounting comfort, and each person can decide depending on the application.
I'm glad the AA not penalize thermal transfer too much in relation to direct solder, when the AA layer is thin.
In the first pic, without high emissivity coating, there is two cold areas at the sides of the direct soldered area. I suppose its where is the kapton. With the coating, it dissapear, so it means the kapton has little influence in overall temp, but have little emisivity, very near the LED, so i think it would be better retire the excess kapton after soldering, especially when the thermal path between the copper plate and heatsink isn't perfect.
For me, your comparison is enough. If anybody wants to do the same but with accurate die temperature measurement, i believe the best way is Vf checking. But its a tough work for little increase in knowledge, as having accurate measurement of lead's temperature allows to compute with little error margin the die temp (knowing the power used (If+Vf) and junction-board thermal resistances, both well known).
For estimating board temperature more accurately, a pic of the copper plate in the other side would be very helpful.
Kinnza Quoting me:
If you think about it a bit more, if there was no spreading thermal resistance, the deltas should have been about the same, with the same power input. But they are not. This would lead me to consider the idea that the die is even more proportionally hotter on the MCPCB mounted one, than what the LED case temperatures are showing.
[CPF-Kinnza]
I didn't read well this paragraph. Nice observation. People not used to FLIR analysis, as me, don't notice this.
So some of my previous statements can be wrong. Maybe the tough work of further research on accurate die temp measurement worth the effort
[CPF-Kinnza]
Good Job
Thank you
[CPF-Kinnza]
I'm glad the AA not penalize thermal transfer too much in relation to direct solder, when the AA layer is thin.
Keeping it thin as possible is key. I put a good amount of weight on it, to make it squish out, to make it thin as possible. I used a piece of pipe with a flat lapped end, over the XR-E, to avoid weight on the dome. Then I put the mass of weight on top of that.
[CPF-Kinnza]
In the first pic, without high emissivity coating, there is two cold areas at the sides of direct soldered. I suppose its where is the kapton. With the coating, it disappear, so it means the kapton has little influence in overall temp, but have little emisivity, very near the LED, so i think it would be better retire the excess kapton after soldering, especially when the thermal path between the copper plate and heatsink isn't perfect.
Actually, it is the Kapton that has much higher emissivity than solder, copper, or aluminum. There is a pre-tinned area on the copper sheet metal, a band that runs left to right. So, if you are trying to radiate the heat, the Kapton works much better. Most bare metals are extremely piss poor thermal radiators at this range of temperatures. In the picture, the Kapton is in the shape of the letter I. I've taken another picture, under different operating conditions, and labeled it (which I had to redo for the later photos, since I found a reflection of me off the surfaces which affects the image). Bare metals also make wonderful mirrors in the true IR regions. See more items labeled below.
[CPF-Kinnza]
For me, your comparison is enough. If anybody wants to do the same but with accurate die temperature measurement, i believe the best way is Vf checking. But its a tough work for little increase in knowledge, as having accurate measurement of lead's temperature allows to compute with little error margin the die temp (knowing the power used (If+Vf) and junction-board thermal resistances, both well known).
I'd definitely have to agree, especially for the flashlight hobbyist folks. The relative comparisons are very useful for checking out different mounting techniques and the relative worthiness of each approach.
[CPF-Kinnza]
For estimating board temperature more accurately, a pic of the copper plate in the other side would be very helpful.
Already tried that, it doesn't work well, as the copper, being a great thermal spreader, you see maybe a 1 degree C delta total, once you have a high emissivity coating. Remember, I am using thicker copper sheet metal, at 0.165" (4.191mm). Otherwise you only see a nice mirror (without coating). By the time you get to the backside, on thin sheet stock aluminum, it works decent. What you end up seeing, on previous testing, is the one that has the highest thermal resistance shows cooler spot when looking at the backside.(since the heat is not being transferred as well)
I can't go too much deeper on things/ideas in this area, as I start getting into proprietary information that I use in my designs at work. Lets just say that I've spent years looking at things, comparing stuff, testing, and I have to be kind of vague on a lot of stuff, or I'm just handing out information to competitors for free.
(And no, I do not work in the flashlight, general lighting, or other related industries. Nor do I have investments or connections in this area)
I've just been spending time here as a "hobbyist", sharing information. knowledge, and ideas with folks to advance the "State of the Art" in flashlights. It is a great way to unwind and relax from much more technical work.
[CPF-McGizmo]
What I take presently from this thread is the consideration that it is likely my present plan of using MCPCB's mounted with XR-E LED's in some lights carries a likely cost of about 5% loss in photometric output as compared to other more ideal means of LED hosting.
Yes, if one takes a very huge leap and tries to assume that case temperatures = die temperatures.
As I pointed out, there are certainly some very major issues with this assumption.
As far as the ring and thermal spreading, take a gander at this picture, realizing that there is quite a bit of magnification of the die image in the XR-E due to the lens effect. The die is only 0.1mm larger in the XR-E vs. this image of the XR7090. Notice how tiny it actually is, the die is the item mounted on top of the much larger ESD diode:
Adding this picture, I cleaned the part up a little:
Oh, I forgot to mention...
This test is at 700mA.
If you drive it beyond that, the differences become even greater, and there is proportionately more light loss due to the extra heat rise caused by the thermal resistance.
Conversely, as you drive them below 700mA, the loss is less.
Please note on the XR-E datasheet, that the light output drop with temp is done at only 350mA. Keep that in mind.
Figured I'd light up the LED shown above, for anyone that is interested:
[CPF-Doug S]
Jar, are you intending to imply that the percentage photometric loss with increasing junction temperature would differ significantly at differing drive currents?
I don't recall ever seeing a reference that suggested this.
Well, lets think about it a bit.
We all know that LEDs get less efficient at higher current levels, and they produce less light at higher currents, and more of the energy leaves the LED die as heat, instead of light.
This is quite apparent in LEDs that are less efficient, such as the Luxeon K2, and the older generations of the OSRAM OSTAR. The light output vs. current curve starts flattening earlier, than a die mounted in a package with lower thermal resistance.
Or, if the LED itself in the system is mounted such that the thermal resistances are higher in relation to ambient (which causes the heat to "accumulate"). Even the thermal emissivity of the heat "radiator" surface comes into play, as it all is part of the system.
Some times the equation changes, sometimes a lot, like in a small flashlight, where if you hold it in your hand, your own body acts as a pretty decent liquid cooling system, to pull heat out of the flashlight, but then you set it down on the counter, floor of the tent, or whatever, where there isn't that much convection nor conduction of the heat, and you have a flashlight with a polished metal finish (low emissivity), and the little light gets amazingly hot.
So, going back, if less light is leaving the die due to lower efficiencies at higher currents, quite obviously the die will be producing more heat.
In the past, where the leading LED efficiencies were rather low, the effect of the additional losses was quite low, since the majority of the power put into the LED left as heat. As LEDs now and especially in the future, get more and more efficient, the contribution of losses in the die at various currents starts to affect the amount of heat generated, which has to travel out of the LED through a given thermal resistance.
The older CREE 7090 chips set records back in 2005, when it was verified at NIST (National Institute of Standards and Technology) they had in fact achieved the 65 lm/W barrier.
http://www.netl.doe.gov/SSL/highlights_cree2.html
Then a little later in SEPTEMBER 2, 2005 it was then announced they had even surpassed that, managing to improve the LED such that they were hitting 70lm/W.
http://www.cree.com/press/press_det...i=1143571750984
If you go back to the first one, where the Department of Energy announced that CREE had hit 65lm/W.
"A key modification to Cree's experimental LED chip design resulted in a 17-20% increase in brightness and, in addition, the demonstration of packaged blue LEDs with external quantum efficiency of 40%."
The packaged blue LED (white LEDs utilize blue LED die in them), in the finished package is actually hitting a 40% quantum efficiency! (yes, I know there are some phosphor losses due to the Stokes effect and other losses in White LEDs)
Several scientists/authors use the maximum perfect theoretical efficiency of a YAG Phosphor + blue LED based White LED (the kind we all use in flashlights) to be 330lm/W. At one of the conferences, they estimated by applying a few known techniques, and with the development of some improvements, white LEDs will reach 155 lm/W- and they felt this was actually realistic.
Anyhow, CREE is getting 70-90 lm/W on parts they are shipping now. Okay, so, why is this important? Well, lets take 80lm/W and divide it by 330 lm/W and you quickly realize the XR-E is running in the range of 24% efficiency!
As a point of reference, if you managed to hold the die temperatures of the first Luxeon I devices down at 25C (not going to happen in a typical flashlight) we were actually seeing efficiencies in the 20lm/W range. 20 lm/W divided by 330 lm/W results in an efficiency of only 6%. Down at these levels, minor changes in the efficiency of the die had very little effect on the overall performance. Even when you start driving the K2 parts at their rated 1.5 Amps you start getting back into the 20lm/W range very quickly (the previous OSRAM OSTAR LEDs driven at spec has much of the same problem).
However, with the CREE XR-E, with it's 24% efficiency, things that used to be minor insignificant items really start to stand out. As the future brings even better devices, with yet higher efficiencies, some of the assumptions that were quite valid and true in the past (since they didn't add up to diddly squat), all of a sudden become outdated and lead folks down the wrong path (a number of old wives tales started this way...)
So, in a way, yes, we need to begin to start and think about a more complex model, if one really want to take full advantage of everything possible. Failure to do so will start leading to extra errors from the assumptions, which can....
[CPF-Kinnza talking about maximum theoretical efficiency of White LEDs]
I already calculated it. The plot of the XR, tint XO, have a luminous efficiency of 310,7 lm/w (507.5 nm centroid wavelength) (about 3% margin error).
So at 75,4 lm/w (reported by NIST in continuos mode) , mean efficiency of 24,25%. At 85 lm/w, which Q2 bins probably reach, means 27,35%.
I think this is not just relevant when considering the slope of the lm degradation at each current. Its very relevant when designing the thermal path. Until now, all LEDs manufacturer consider the light emission negligible when calculating the total thermal load, because it was below 10%, but when efficiencies reach 25%, it means 1/4 less heat to dissipate, and probably more, as the blue led is emitting at higher efficiency, as part of its emission is lost at phosphor conversion.
Very nice!
Thank you very much for all the effort.
Wavelength precision ±0.3nm (median wavelength: 546.1nm Hg lamp)
Wavelength resolution 0.9nm/pixel
Repeatability (σ )
(For Illuminant A)
Normal Mode Luminance: 0.1%, +1 digit
Chromaticity x y: 0.0002 over the Luminance range
The relative shape is correct here, but not the absolute value. This is in WATTS/sr*m^2*nm (NOT Photopic numbers, so you'll need to adjust for that)
380 8.24E-05
381 3.64E-06
382 2.14E-05
383 0.00E+00
384 3.90E-05
385 4.48E-06
386 1.55E-06
387 6.45E-07
388 2.60E-05
389 1.49E-05
390 2.22E-05
391 2.99E-05
392 7.21E-05
393 0.00E+00
394 0.00E+00
395 0.00E+00
396 0.00E+00
397 0.00E+00
398 0.00E+00
399 0.00E+00
400 0.00E+00
401 0.00E+00
402 0.00E+00
403 9.19E-06
404 1.28E-05
405 0.00E+00
406 7.39E-05
407 1.01E-04
408 2.12E-05
409 1.41E-04
410 2.30E-04
411 4.15E-04
412 5.01E-04
413 7.24E-04
414 9.76E-04
415 1.36E-03
416 1.70E-03
417 2.17E-03
418 2.82E-03
419 3.59E-03
420 4.51E-03
421 5.73E-03
422 7.28E-03
423 9.00E-03
424 1.08E-02
425 1.28E-02
426 1.51E-02
427 1.76E-02
428 2.06E-02
429 2.40E-02
430 2.75E-02
431 3.15E-02
432 3.57E-02
433 4.05E-02
434 4.55E-02
435 5.10E-02
436 5.68E-02
437 6.30E-02
438 6.95E-02
439 7.65E-02
440 8.40E-02
441 9.21E-02
442 1.01E-01
443 1.09E-01
444 1.19E-01
445 1.29E-01
446 1.40E-01
447 1.51E-01
448 1.63E-01
449 1.74E-01
450 1.86E-01
451 1.97E-01
452 2.07E-01
453 2.15E-01
454 2.22E-01
455 2.27E-01
456 2.29E-01
457 2.29E-01
458 2.27E-01
459 2.22E-01
460 2.16E-01
461 2.08E-01
462 1.98E-01
463 1.87E-01
464 1.76E-01
465 1.66E-01
466 1.57E-01
467 1.48E-01
468 1.39E-01
469 1.31E-01
470 1.24E-01
471 1.19E-01
472 1.14E-01
473 1.09E-01
474 1.04E-01
475 9.96E-02
476 9.53E-02
477 9.11E-02
478 8.72E-02
479 8.34E-02
480 7.97E-02
481 7.61E-02
482 7.27E-02
483 6.97E-02
484 6.70E-02
485 6.46E-02
486 6.25E-02
487 6.07E-02
488 5.92E-02
489 5.80E-02
490 5.70E-02
491 5.62E-02
492 5.55E-02
493 5.49E-02
494 5.46E-02
495 5.45E-02
496 5.46E-02
497 5.49E-02
498 5.53E-02
499 5.59E-02
500 5.67E-02
501 5.77E-02
502 5.87E-02
503 6.00E-02
504 6.15E-02
505 6.29E-02
506 6.47E-02
507 6.63E-02
508 6.80E-02
509 6.99E-02
510 7.18E-02
511 7.36E-02
512 7.55E-02
513 7.74E-02
514 7.93E-02
515 8.12E-02
516 8.30E-02
517 8.49E-02
518 8.65E-02
519 8.83E-02
520 9.00E-02
521 9.17E-02
522 9.32E-02
523 9.48E-02
524 9.63E-02
525 9.78E-02
526 9.91E-02
527 1.00E-01
528 1.02E-01
529 1.03E-01
530 1.04E-01
531 1.05E-01
532 1.06E-01
533 1.07E-01
534 1.08E-01
535 1.08E-01
536 1.09E-01
537 1.10E-01
538 1.10E-01
539 1.11E-01
540 1.12E-01
541 1.12E-01
542 1.13E-01
543 1.13E-01
544 1.13E-01
545 1.14E-01
546 1.14E-01
547 1.14E-01
548 1.14E-01
549 1.14E-01
550 1.14E-01
551 1.14E-01
552 1.14E-01
553 1.14E-01
554 1.14E-01
555 1.14E-01
556 1.14E-01
557 1.14E-01
558 1.14E-01
559 1.14E-01
560 1.14E-01
561 1.14E-01
562 1.14E-01
563 1.14E-01
564 1.14E-01
565 1.13E-01
566 1.13E-01
567 1.13E-01
568 1.13E-01
569 1.12E-01
570 1.12E-01
571 1.12E-01
572 1.11E-01
573 1.11E-01
574 1.11E-01
575 1.10E-01
576 1.10E-01
577 1.09E-01
578 1.09E-01
579 1.08E-01
580 1.08E-01
581 1.07E-01
582 1.06E-01
583 1.06E-01
584 1.05E-01
585 1.04E-01
586 1.04E-01
587 1.03E-01
588 1.02E-01
589 1.01E-01
590 1.01E-01
591 9.98E-02
592 9.90E-02
593 9.82E-02
594 9.73E-02
595 9.64E-02
596 9.56E-02
597 9.47E-02
598 9.39E-02
599 9.30E-02
600 9.21E-02
601 9.13E-02
602 9.04E-02
603 8.96E-02
604 8.87E-02
605 8.78E-02
606 8.70E-02
607 8.61E-02
608 8.53E-02
609 8.45E-02
610 8.38E-02
611 8.31E-02
612 8.22E-02
613 8.14E-02
614 8.04E-02
615 7.94E-02
616 7.85E-02
617 7.76E-02
618 7.67E-02
619 7.59E-02
620 7.50E-02
621 7.42E-02
622 7.33E-02
623 7.24E-02
624 7.15E-02
625 7.06E-02
626 6.98E-02
627 6.89E-02
628 6.79E-02
629 6.70E-02
630 6.61E-02
631 6.52E-02
632 6.42E-02
633 6.32E-02
634 6.23E-02
635 6.13E-02
636 6.03E-02
637 5.94E-02
638 5.85E-02
639 5.76E-02
640 5.67E-02
641 5.58E-02
642 5.49E-02
643 5.40E-02
644 5.31E-02
645 5.22E-02
646 5.13E-02
647 5.04E-02
648 4.95E-02
649 4.86E-02
650 4.77E-02
651 4.68E-02
652 4.59E-02
653 4.51E-02
654 4.44E-02
655 4.41E-02
656 4.33E-02
657 4.25E-02
658 4.17E-02
659 4.09E-02
660 4.01E-02
661 3.94E-02
662 3.86E-02
663 3.80E-02
664 3.72E-02
665 3.65E-02
666 3.57E-02
667 3.50E-02
668 3.43E-02
669 3.36E-02
670 3.29E-02
671 3.23E-02
672 3.16E-02
673 3.09E-02
674 3.03E-02
675 2.97E-02
676 2.91E-02
677 2.85E-02
678 2.79E-02
679 2.73E-02
680 2.68E-02
681 2.62E-02
682 2.57E-02
683 2.51E-02
684 2.45E-02
685 2.40E-02
686 2.36E-02
687 2.31E-02
688 2.27E-02
689 2.21E-02
690 2.16E-02
691 2.11E-02
692 2.05E-02
693 2.01E-02
694 1.96E-02
695 1.92E-02
696 1.88E-02
697 1.85E-02
698 1.81E-02
699 1.77E-02
700 1.72E-02
701 1.68E-02
702 1.65E-02
703 1.62E-02
704 1.58E-02
705 1.55E-02
706 1.51E-02
707 1.49E-02
708 1.45E-02
709 1.41E-02
710 1.38E-02
711 1.35E-02
712 1.31E-02
713 1.28E-02
714 1.25E-02
715 1.22E-02
716 1.19E-02
717 1.16E-02
718 1.14E-02
719 1.11E-02
720 1.10E-02
721 1.07E-02
722 1.04E-02
723 1.02E-02
724 1.00E-02
725 9.83E-03
726 9.58E-03
727 9.41E-03
728 9.19E-03
729 8.92E-03
730 8.72E-03
731 8.61E-03
732 8.39E-03
733 8.21E-03
734 8.01E-03
735 7.86E-03
736 7.71E-03
737 7.49E-03
738 7.42E-03
739 7.25E-03
740 7.09E-03
741 6.93E-03
742 6.75E-03
743 6.61E-03
744 6.47E-03
745 6.29E-03
746 6.16E-03
747 6.10E-03
748 5.98E-03
749 5.87E-03
750 5.74E-03
751 5.52E-03
752 5.54E-03
753 5.44E-03
754 5.32E-03
755 5.14E-03
756 5.10E-03
757 4.87E-03
758 4.90E-03
759 4.84E-03
760 4.73E-03
761 4.58E-03
762 4.51E-03
763 4.47E-03
764 4.46E-03
765 4.32E-03
766 4.31E-03
767 4.24E-03
768 4.14E-03
769 4.03E-03
770 3.97E-03
771 3.79E-03
772 3.82E-03
773 3.86E-03
774 3.77E-03
775 3.64E-03
776 3.70E-03
777 3.50E-03
778 3.55E-03
779 3.58E-03
780 3.50E-03
If you get the conversion correct, the 2 degree CIE observer should put you at x= 0.3105 and y= 0.3241, Kelvin Temp 6660.
[CPF-Kinnza]
I calculated again with the more accurate data you provided, Newbie. I obtain 276,5 lm/w of luminous efficacy. I don't know if the last data correspond to a slightly different spectrum. I used a pic of a XR-E spectrum with a color temp of 6402K, and obtained the 310,7lm/w figure, but getting the data directly from the graph (obviously, less accurate). If i understood well, the new data is from a XR-E with a 6600K color temp, corresponding to 276,5 lm/w, so for this more bluish color, same photopic emission correspond to higher efficiency.
http://www.ecse.rpi.edu/%7Eschubert...hromaticity.jpg
This is a pic showing the luminous efficacy obtained depending of chromaticity coordinates. Mixing it with each tint coordinates can provide the range of luminous efficacy of any tint.
I made a Excel sheet to compute the luminous efficacy. Can anybody suggest me a good file server to put it? Anyway, i can send it for mail to anybody wanting to check the procedure used (or just to get the CIE photopic curve per nm values).
BTW, yesterday i saw this: New LED junction temperature tester.
At the bottom, there is a link to the product page, which explains the procedure used.
If you poke around on the Aglient site (it may have moved over to Avago's site now), they have a paper on how to measure the internal junction temperature with an electrical setup.
Found it:
http://www.molalla.net/~leeper/ledtherm.pdf
Another method:
http://www.elecdesign.com/Articles/...ArticleID=11676
BTW Anglepoise, I wanted to thank you for sacrificing that LED! Nice
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