German Modder Vinz uses self-made diamond based thermal glue. It has 85% synthetic diamond content. The diamond has a thermal conductivity of 3300 W/(m·K). It theoretically has a better thermal conductivity than copper. He doesn’t use it for the central thermal pad though. He uses normal DTP copper pcbs and a solder with a high silver content, Mundorf MSolder Silver Gold. This solder is very expensive unfortunately (50€ for a 100g roll). MSolder Silver Gold Supreme has an even higher Silver content (9.6g instead of 3.8g), but it’s twice as expensive.
I would prefer we talk about more fundamental changes. Using better solder will not increase the luminance by visible amounts. How do we get from 300cd/mm2 to 500 or even 1000?
I would expect Indium-Silver to have better conductivity than pure indium, but according to Indium Corp that’s not the case:
Too bad MSolder doesn’t list conductivity of their solder….though Indium Corp shows a similar 96.5Sn3.5Ag to have 33 W/mK. And this one at 78 W/nK :person_facepalming:
This “almost” is 7.4 °C for XHP35 at full power. It’s hard to look at the Cree charts, but to my eye it’s very roughly half bin upgrade. For Blackie the difference would be 4 °C. 2% flux difference? Not a big deal, but if I were chasing records and could verify purity, I would spent the $10 without a blink.
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Well, though without knowing solder joint thickness that we get with our methods, the numbers above may be significantly off in any direction.
Yes, in that case it’s worth it to do every little thing. That’s why Vinz does it. His Mjölnir light used to have an XM-L2 which ran at 7.5A for 30s (after that the drivers reduces to 7A). Nobody “pushed” more current through that LED!
I have added the Luminus SBT-70 because it's unique in that it has many of the right features (large solder pad, low thermal resistance, no dome, cool-white low cri), but is hindered by it's low efficiency (43.7 - 46.7 lm/W at max brightness). I still like it though because of it's unique beam when used with aspheric lenses and the high light quality of the WDH (cool white, high-cri, high R9) version.
Getting those values was a lot of work.
Here sma measured the luminance of an SBT-70 from 2012 in an Olight SR-95S UT host. It did 71cd/mm^2 at 10.6A. Back then the LED had just come to the market and Olight couldn't have gotten the best bins which were available in the following years. Unfortunately they don't state the used bin in the description of the light. This promotional picture says "up to 1700 lumens". I checked an older datasheet and it has a Bin which goes up to 1710 lumens at the maximum current of 10.5A, the NA-Bin. In the latest datasheet version the best Bin is the PB-Bin. LEDs in this bin are 22.8% brighter compared to those in NA-Bin. So now we are at 87.2cd/mm^2. Now we need to find out at what current the LED reaches it's maximum brightness and how much brighter it becomes. Unfortunately there are no real tests of this LED. DB Custom has reported that it does 18.75A in direct-drive with a 26650. I took a closer look at the brighness curve in the datasheet and also compared it to the SST-90 (slightly larger 9mm^2 die) which is rated up to 18A. From 3.5A to 10.5A the SST-90 becomes 125% brighter and the SBT-70 only 122%. This makes sense because it has a smaller die. I concluded that the maximum current must also be lower. By extrapolating the curve I could see that it reaches it's maximum at around 15A and 3.91V. Other people and also myself have measured much lower Vfs compared to the datasheet values (which are measured at 25°C though...). So I assume a Vf of 3.6V at 15A and a brightness increase of 20% from 10.5A to 15A. That gives us 105cd/mm^2, 15A, 54W, the values I put into the table.
I really wonder why the brightness curve is so flat. At 54W and 25°C heatsink temp it only has junction temperature of ~64°C. The main reason why the newer CFT-90 is so much better is because it can handle almost twice the temperature.
My guess is that a new generation of 445nm laser pumped white light diodes will probably come out at some point that increase the luminance by a few 100% there should be not that much of a problem to produce this in a similar package than the LEDs are now
Yes, I agree that lasers can be very small as well, although I don’t think this it too important. They are small enough already. The problem with lasers is that they are less robust and require better cooling compared to LEDs.
I just had the idea that one could seperate the phosphor of an LED from the die by using a piece of short glass fiber. This could result in higher output.
That depends. How hot does the Phosphor get when it is part of a LED? Is it hotter or cooler than the die? Does it heat up more because of the heat emitted by the blue die or by the inefficiency of the conversion process?
At first I dismissed this comment. After all, we BLFers won’t have our own custom LED. But then I started thinking…LED construction may be too hard for us amateurs, but there are quite a few companies which have all the skills and tools. Especially that we don’t need to build everything from scratch. Companies like Cree sell individual dies or phosphors.
Now the question is: what are R&D costs? What are unit costs? What volume would be needed to make this possible?
I have no idea what are the answers to any of these questions. I’d like to have it.
I don’t know. I would imagine that it is unbelieveably expensive.
The LED I mention above would probably need to be made by Luminus or maybe Osram. As far as I know only they offer direct mounted LEDs. Those LEDs are different compared to Cree, Nichia etc.
Theoretically, if the LED has no dome or flat dome they will all have the same spatial distribution following cos(theta)
However I have calculated the lm/mm^2 of many LEDs and it does not match up at all with the measured cd/mm^2 so there is definitely some other variable(s) affecting the intensity.
Real world testing is the most accurate method atm.
I added the new Osram Square Flat. Together with the Luxeon Z ES it’s the only XP-G2 sized LED which comes without a dome. It has a low thermal resistance, only the XP-G2 is even better.
If you list pad size to 3 decimals, your number for Osram Square Flat KW CSLPM2.PC is wrong.
You missed that the thermal pad corners are rounded, so the pad is 2.629 mm².
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Also, there’s some controversy regarding Osram Ostar LE UW Q8WP NB, so the listed luminosity may be too high.
You are correct, thanks. I guess I was too lazy for that:)
I agree regarding the fact that there is controversy, but I would prefer actual throw measurements with a reflector to back those values up.
I will also add Köf3’s mneasured values of the Luxeon V.
