Future development of the maximum luminance of LEDs

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.

ADDED:
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.

I know this post is a bit old but I wanted to mention that diamond is 2200W/mk not 3300, and that thermal compounds made of diamond do not actually work very well.
ICdiamond only has ~10w/mk.
The way to get the best thermal connection is to use liquid metal such as coolaboratory liquid ultra/pro or thermal grizzly conductonaut.
The pro and conductonaut have ~76W/mk.
Using this is a better choice than solder because being a liquid it can contact all the small cracks and crevices.
If you tried to solder a copper MCPCB to a copper heatsink it would be almost impossible to get a perfect joint due to the large area and how fast the heat moves away.
High silver content in solder also gives a higher thermal conductivity, about 70-80 IIRC, but it makes pretty much no noticeable difference.
I use 3% silver/tin solder for all of the stuff I do.

Applying and removing the liquid metal is actually really easy to do.
Having an easily removable MCPCB is great, I don’t recommend people solder their MCPCBs to a heatsink.

There are 2 problems with Conductonaut though:

  • it is rated to 140 °C, so you can’t use it together with soldering (although I don’t know what happens once you exceed that temp).
  • it is fluid which means there’s a risk of run-out. Or pump-out.

The LED should never exceed 140C.
If you use liquid metal there is no need to solder anything, that’s the entire point of using it instead of soldering.
If you mean soldering the LED to the MCPCB, you do that before you put the MCPCB on the heatsink and apply thermal compound.

Also if you apply it correctly there is nothing that comes out.
If you overapply and some comes out around the MCPCB you can just wipe it off.
Nothing else from below the MCPCB will come out so it is completely safe.
This is assuming the MCPCB is securely screwed down of course.

I meant using it on the thermal pad of a led while joining electric pads otherwise. If the other joining method is soldering - LM seems off the table. If it’s glueing heat is not a problem.

There was quite a number of people reporting how Conductonaut leaked and caused shorts inside their laptops. That’s why people recommend CLU there - it’s thicker.

I don’t know where he got the number, different places state different things. A range makes more sense to me than a single value. The highest I have read is 2500.

I do find it interesting though that you stated that it doesn’t work that well because this one company can’t or won’t do it that good.

In the end polishing the surfaces will reduce the effect of the paste anyhow. Vinz preferred this stuff especially for potting his lights.

I think it could be used for replacing a DTP pcb. That would be interesting.

Oh I see.
Yeah liquid metal wouldn’t be ideal to use so close to the LED pads.
For stuff like the synios LEDs though the thermal pad is also the cathode so it needs to be soldered anyway.
Using conductonaut between the MCPCB and heatsink is fine, it does not seep out the sides.

I just double checked, the 3300 is for single crystal artificially made synthetic diamonds. Apparently moissanite also has a high thermal conductivity close to diamond.

Still, diamond isn’t fluid so the best that can be done is grinding it into powder and putting it inside another thermal compound.
Due to the surface tension of liquid metal, I doubt it the diamond dust would mix well with that while still allowing good contact between the fluid and solid grains.

This is most likely why the only diamond thermal compounds are regular viscous pastes and not liquid metals.
Instead of having a uniform mixture it has to go mediocre thermal compound -> diamond grain -> mediocre thermal compound -> diamond grain over and over again, which likely leads to the bad performance.

Did you perform drop tests?

Uh, no, if I dropped a $2000 11lb light I would have much bigger problems than a tiny drop of liquid metal.

But just from looking at it, the gap between the mcpcb and heatsink is so small that the liquid metal can’t run out.
The only runout happens if you apply too much initially, it can seep out when you tighten the MCPCB down, but as I said you can just wipe that off.

I meant that this tiny drop can damage your $400 reflector.
And also that I simply don’t like general statements like “Using conductonaut between the MCPCB and heatsink is fine, it does not seep out the sides.” as they may not be always applicable.

You could put expoxy or similar around the sides of the pcb to seal it off.

Or you could grind and polish both surfaces to perfect flatness. Are you gonna do that?

The liquid metal simply rolls off of a surface unless it is purposefully rubbed in using the swab it comes with.
Kinda like mercury where it just forms small balls that don’t stick.

The only concern using liquid metal is that it is conductive and can short stuff which is why you need to be very careful using it in a PC.
Here, worst case scenario is that a $5 LED driver gets fried.

But no, I can say that there is certainly not going to be any liquid metal coming out from between the MCPCB and cooling block, there is literally a few microns of space and it is impossible for a fluid with such high surface tension to seep out.
This is like being concerned that regular thermal paste will leak out from between a CPU and heatsink due to them not being perfectly flat together. It simply never happens. The only stuff that can possibly come out is during the initial application.

The block is faced on a lathe and the MCPCB is perfectly flat as far as I can tell.
Any polishing I try to do would make things worse.
The liquid metal already gives a large improvement over thermal paste, and that only results in slightly higher current handling.
The only thing which would possibly be of any further improvement is directly lapping both surfaces together, but that would take tens or hundreds of hours for basically 0 improvement (in temperatures).

It’s extremely corrosive to aluminium.

Yes, exactly. Get liquid metal on any aluminium part and that part will be gone soon. The aluminium will simply fall into pieces :smiley:

Also Copper + Copper might be a more eternal joint than you would hope, although there is no danger of the copper being corroded away by the liquid metal. If the copper is gold plated like on most boards, this won’t be a problem though.

Yes I have always known that liquid metal reacts with aluminum.
The MCPCB and block are both copper.
As I said before, there is no risk of any liquid metal coming out anyway, there is a fraction of a gram compressed between the two pieces of metal and not enough space for it to exit.
And again, as I said before, even if there is a drop, it forms a ball just like mercury that rolls off of a surface, it does not stick.
It would not cause any damage to the aluminum on the reflector unless it was rubbed onto the surface such that it broke the surface tension and made contact. This would also require a lot more liquid metal than is even applied in the light.

It’s honestly not as scary as people make it out to be.
You even get a ton of applications with the 1g syringe, like more than 10.

I have updated the table because more practical tests have shown that the Synios LEDs are not quite as good as we thought. The luminance of the CFT-90 is also not certain yet. Vinhnguyen54 got 1.58Mcd in a BLF GT and 900kcd in a TN-42 at sub-maximal current. I don’t know of any other values.

He said he got just 20 amps in GT. Frankly, it beats me why so low.
Maybe he posted it as a conservative number that any modded light will reach with much used batteries, but anyway he has a lot of headroom.

Maybe there are too many losses in the main springs.
It’s also a DD light. It’s difficult to base anything off of those kinds of measurements. Measuring high currents obviously needs to be done correctly, otherwise the measurement will reduce the actual current.