# Oil cooled LED



## marcopolo (Dec 12, 2009)

Has anyone tried or thought of filling the front end of an LED light with oil to cool the LEDS? Obviously it would have to be sealed well from the back end round cables etc...but if it was possible and any case design is good so that the residual heat is still dissipated to the air then it would cool the LED's much more efficiently.

Marco.


----------



## Illum (Dec 12, 2009)

I've once proposed of potting the electronics and filling a light and its internals with pure, de-ionized water turning the internal effectively as a heatsink. Still air is a good insulator, which occupies most of the reflector assembly.

Mineral oil could be a potential medium, it should prevent airborne oxidation but may inhibit mechanical interaction in terms of metal contacts, focusing assemblies, or switches.

Like all things too, prepare for a little positive pressure as all things expand when heated.


----------



## balou (Dec 12, 2009)

One thing to consider is the change in optical properties when switching from air to oil.
I just don't know if the changes would be for better or for worse.


----------



## Illum (Dec 12, 2009)

balou said:


> One thing to consider is the change in optical properties when switching from air to oil.
> I just don't know if the changes would be for better or for worse.



well... I find that lambertian radiation pattern, batwing, and side emitting all looked the same under water, so yes...focus would be different, if there were bubbles [or air bells] in the fluid expect a heavy loss in lumens


----------



## saabluster (Dec 12, 2009)

marcopolo said:


> Has anyone tried or thought of filling the front end of an LED light with oil to cool the LEDS? Obviously it would have to be sealed well from the back end round cables etc...but if it was possible and any case design is good so that the residual heat is still dissipated to the air then it would cool the LED's much more efficiently.
> 
> Marco.


It has been proposed here more than once. I seem to remember even seeing research into that idea not too long ago.


----------



## Burgess (Dec 12, 2009)

Illum said:


> I've once proposed of potting the electronics and filling a light and its internals with pure, de-ionized water
> turning the internal effectively as a heatsink.
> 
> Like all things too, prepare for a little positive pressure as all things expand when heated.


 

I can tell you live in *Florida*. 


Here in the "Real World", we have COLD temperatures,
which would turn that pure water into pure ICE.


Thereby generating more than a little positive pressure.




Still, an interesting concept.


----------



## jtr1962 (Dec 12, 2009)

It doesn't make any sense to do this from a thermal or manufacturing standpoint. This would be harder to make than something with a traditional aluminum heat sink. If you make the liquid container out of glass, you lose one of the primary selling points of LED lamps-namely durability. And ultimately, you're limited by the form factor of the bulb, which in turn limits your surface area. In the end it doesn't matter whether you use metal or liquid to move the heat away from the LED, the fact remains that you need surface area to dissipate this heat. An A19 bulb form factor has a very limited amount of that unfortunately. This concept actually sounds much more promising than using liquid.


----------



## Lynx_Arc (Dec 12, 2009)

I don't think I would want an oil filled light, nothing like having it leak oil all over you.


----------



## Roger Sully (Dec 12, 2009)

Lynx_Arc said:


> I don't think I would want an oil filled light, nothing like having it leak oil all over you.


 
and then your batteries choosing that very moment to go vent..with flame


----------



## SemiMan (Dec 12, 2009)

Of course there is the fact that almost all the heat comes out the back of the LED into the mounting point.

Semiman


----------



## blasterman (Dec 13, 2009)

Actually an oil / liquid filled fixture works against cooling. A sphere of liquid, even if it were theoretically molten metal with high thermal conductivity, has far less surface area than radiating fins occuyping the same space.


----------



## saabluster (Dec 14, 2009)

blasterman said:


> Actually an oil / liquid filled fixture works against cooling. A sphere of liquid, even if it were theoretically molten metal with high thermal conductivity, has far less surface area than radiating fins occuyping the same space.





SemiMan said:


> Of course there is the fact that almost all the heat comes out the back of the LED into the mounting point.
> 
> Semiman



I wonder if there is a misunderstanding here. Since the title of the thread is "Oil cooled LED" I took this to mean that he was referring to the liquid flowing over the die itself. And it doesn't sound like he is talking about liquid cooling replacing the normal cooling via conduction through the back to a heatsink. 



marcopolo said:


> Has anyone tried or thought of filling *the front end* of an LED light with oil to cool the LEDS?


(Emphasis mine)

Radiating fins on the front of the die is laughable to say the least. The idea of cooling the front of the die has merit. It also does not preclude the normal heat path as well. Alas there are massive hurdles with the idea that would most likely make it something only worth doing in a lab to show off.


----------



## znomit (Dec 14, 2009)

Oh here we go, hydralux.







http://www.treehugger.com/files/2009/07/whats-so-special-about-hydralux.php

CPF thread.


----------



## marcopolo (Dec 14, 2009)

Hi guys ther does appear to be a small amount of misunderstanding. Take a light case, any case with fins etc......Fill the front end of the case with oil and seal up. That is the end with the optics LED's mounted on MCPCB etc...Seal up any holes to the back of htecase ie that wires pass through to driver switch etc...

The heat would be radiated far faster to the fins on the case.

When I do temperature measurements so set cut off etc..I place the temp probe on the FRONT of the LED. This shows just how much heat is also radiated from the front of the LED and so why I think it would benefit from cooling in CONJUCTION with a standard finned case.


----------



## jtr1962 (Dec 14, 2009)

marcopolo said:


> When I do temperature measurements so set cut off etc..I place the temp probe on the FRONT of the LED. This shows just how much heat is also radiated from the front of the LED and so why I think it would benefit from cooling in CONJUCTION with a standard finned case.


No, the temperature probe gets hot because the visible light from the LED is converted to heat when the temperature probe absorbs it, not because the LED is emitting heat out the front. LEDs emit nothing in the infrared. What comes out the front is visible light, and remains visible light unless absorbed by an object and converted to heat. By putting oil or anything else in front of an LED you're actually absorbing some of that visible light, and converting it to heat. This isn't helping to cool the LED one bit. All it's doing is decreasing the visible output.

In short, it's great you're thinking outside the box, but in fact if this idea had any merit the LED industry would have been all over it years ago. Same thing with using peltiers to cool LEDs. Every few months we get another thread on that. Now I just copy and paste my answers from the last thread into the present one.

The Hydralux bulb uses oil for a different reason-namely as a conduction medium between an internal heatsink and the outer surface of the bulb. Still a pointless idea as the flat bulb has less surface area to ultimately dissipate the heat than a traditional finned heat sink. The claimed "benefit" is that the oil spreads the light out past 180°. I personally don't see how this is a benefit as a light source with a spread of 180° or _less_ is ideal, provided it's mounted face down on a ceiling. Any light past 180° ends up being partially or entirely wasted inside the fixture. So even here it isn't really a great idea. Not to mention that the Hydralux bulb lacks one of the major benefits of LED lighting-namely durability.


----------



## saabluster (Dec 14, 2009)

marcopolo said:


> Hi guys ther does appear to be a small amount of misunderstanding. Take a light case, any case with fins etc......Fill the front end of the case with oil and seal up. That is the end with the optics LED's mounted on MCPCB etc...Seal up any holes to the back of htecase ie that wires pass through to driver switch etc...
> 
> The heat would be radiated far faster to the fins on the case.
> 
> When I do temperature measurements so set cut off etc..I place the temp probe on the FRONT of the LED. This shows just how much heat is also radiated from the front of the LED and so why I think it would benefit from cooling in CONJUCTION with a standard finned case.


Well if thats what you mean then that is not such a great idea. Sorry. Heavier, prone to catastrophic failure, ineffective, lumen reducing. That's just off the top of my head. You cannot conduct enough heat through an LED's package to be of any benefit to the LED itself.


----------



## wapkil (Dec 14, 2009)

jtr1962 said:


> No, the temperature probe gets hot because the visible light from the LED is converted to heat when the temperature probe absorbs it, not because the LED is emitting heat out the front. LEDs emit nothing in the infrared. What comes out the front is visible light, and remains visible light unless absorbed by an object and converted to heat. By putting oil or anything else in front of an LED you're actually absorbing some of that visible light, and converting it to heat. This isn't helping to cool the LED one bit. All it's doing is decreasing the visible output.



I'm not sure if I understand you correctly but the LED's dome can also become quite hot. I guess the reason is mainly conduction, not radiation but either way lowering the thermal resistance from the dome to ambient should lower the LED temperature, shouldn't it? 

The glass in Cree LEDs, for example, is a poor conductor when compared to metals but a really good one compared to the surrounding air. Filling the light head with oil doesn't seem to be a good idea but I think that it should somehow improve the heat transfer and lower the LED temperature :shrug:

EDIT: What was most surprising for me, was the idea that the probe gets hot because of the radiation it absorbs. I always thought that when I touch the thermocouple to the LED dome, what I measure is the actual dome temperature, not the massive amount of radiation that would be needed to rise the probe temperature...


----------



## blasterman (Dec 14, 2009)

> but in fact if this idea had any merit the LED industry would have been all over it years ago.


 I also have a suspicion it has a lot to do with oil being cheaper than a block of aluminum or a custom designed heat-pipe.

So far, Evolux seems to have the only practical option with retrofits in just using a high duty fan.


----------



## saabluster (Dec 14, 2009)

wapkil said:


> I think that it should somehow improve the heat transfer and lower the LED temperature :shrug:


Nope. It will not make an appreciable difference in junction temps. Junction temperature is all that matters not the surface temp of the package.


----------



## bshanahan14rulz (Dec 14, 2009)

Although somewhat off-topic, technically the rebel has cooling on the front of the die.... right?

And what if the oil were to act as a heat spreader instead, and it pumped into a radiator, a la steampunk artsy stuff?


----------



## jtr1962 (Dec 14, 2009)

wapkil said:


> EDIT: What was most surprising for me, was the idea that the probe gets hot because of the radiation it absorbs. I always thought that when I touch the thermocouple to the LED dome, what I measure is the actual dome temperature, not the massive amount of radiation that would be needed to rise the probe temperature...


You can vividly demonstrate this by putting a piece of black electrical tape over the dome of a Rebel or an XP-E/XP-G. The tape will start smoking almost immediately. On the other hand, do the same with a piece of white paper or clear tape, and nothing happens. This is telling me the dome doesn't get that hot in normal use. Rather, it is the emitted light energy being absorbed which makes some ( but not all ) objects placed near the dome get hot. And if you physically think about this it makes sense. Today's emitters can emit upwards of 100 lumens of light from a very tiny surface area. The efficacy of the emitted spectrum is around 330 lm/W, so 100 lumens equates to 100/330, or about 0.3 watts, of light energy. Think how a small component like a surface mount resistor gets when it dissipates 0.3 watts. And if you put a probe or black tape or your finger over the dome it will absorb roughly that much power. This is a relatively new, interesting phenomenon. A few years ago LED domes were much larger, and they emitted far less light, so the temperature rise experienced by objects in proximity to the dome was negligible.

But the fact remains that nearly 100% of the heat an LED produces is conducted to the thermal pad. Oil cooling of the dome will accomplish absolutely nothing.


----------



## wapkil (Dec 14, 2009)

jtr1962 said:


> You can vividly demonstrate this by putting a piece of black electrical tape over the dome of a Rebel or an XP-E/XP-G. The tape will start smoking almost immediately. On the other hand, do the same with a piece of white paper or clear tape, and nothing happens. This is telling me the dome doesn't get that hot in normal use. Rather, it is the emitted light energy being absorbed which makes some ( but not all ) objects placed near the dome get hot. And if you physically think about this it makes sense. Today's emitters can emit upwards of 100 lumens of light from a very tiny surface area. The efficacy of the emitted spectrum is around 330 lm/W, so 100 lumens equates to 100/330, or about 0.3 watts, of light energy. Think how a small component like a surface mount resistor gets when it dissipates 0.3 watts. And if you put a probe or black tape or your finger over the dome it will absorb roughly that much power. This is a relatively new, interesting phenomenon. A few years ago LED domes were much larger, and they emitted far less light, so the temperature rise experienced by objects in proximity to the dome was negligible.



The light undoubtedly conducts energy but as I understand, we are talking about a small, fraction of a cubic millimeter size, thermocouple head. It also usually has a shining, metallic surface. It's hard for me to imagine how much radiation would have to be emitted around to significantly rise its temperature.

When I was measuring LED dome temperatures, the readings were starting to rise rapidly only after the thermocouple physically touched the dome. Moreover, after the light was turned off the measured temperature didn't drop rapidly as it would if the thermocouple was heated by radiation. I still suspect that it was a result of a simple heat conduction. It is probably sufficient to touch the dome after the light is turned off to see that it becomes quite hot 



saabluster said:


> Nope. It will not make an appreciable difference in junction temps. Junction temperature is all that matters not the surface temp of the package.





jtr1962 said:


> But the fact remains that nearly 100% of the heat an LED produces is conducted to the thermal pad. Oil cooling of the dome will accomplish absolutely nothing.



I think I have to agree with you here. Even if I'm right that the dome is not exactly an insulator (AFAIR glass has thermal conductivity comparable to thermal pastes) it is definitely much worse than aluminum. What is worse, if I'm correct one should fill up the head with glass instead of water or oil to effectively transfer the heat in a relatively transparent medium and even with glass, in a properly designed flashlight the gain would probably be negligible.


----------



## jtr1962 (Dec 14, 2009)

wapkil said:


> The light undoubtedly conducts energy but as I understand, we are talking about a small, fraction of a cubic millimeter size, thermocouple head. It also usually has a shining, metallic surface. It's hard for me to imagine how much radiation would have to be emitted around to significantly rise its temperature.


Again, think about the physics of this. What really causes the temperature to rise here is the _intensity_ of the light falling on the probe. Very close to the dome this can be two orders of magnitude higher than full sunlight! Granted, the probe may be small and not a perfect absorber. Nevertheless, it is still subject to the same light intensity at any given distance from the dome as black electrical tape. And because it has a small mass, it doesn't require as much energy to heat up. I already have noted this effect with my outdoor thermometer probe. It's white and therefore doesn't absorb much light. Nevertheless, in full sunlight it can be as much as 20°F higher than the shade temperature. Sunlight has a large component of infrared contributing to the heating, so this isn't a totally fair comparison. Nevertheless, I think visible light contributes at least 1/3 to the temperature rise, so if you want to correct for this you might say the probe rises up to 6°F due to visible light absorption. Close to the dome of a small power LED the visible light intensity can be two orders of magnitude greater than full sunlight. So that's potentally 100 times as much temperature rise. In reality it's less, because as an object heats up, it also starts convecting and radiating away some of the energy. The temperature it ultimately stabilizes at depends upon how well it absorbs energy versus how well it loses it as it heats up. Anything black and with low surface area (i.e. flat ) will get very hot in sunlight. Something like an aluminum heatsink with lower absorption and more surface area will experience far less temperature rise.



> When I was measuring LED dome temperatures, the readings were starting to rise rapidly only after the thermocouple physically touched the dome. Moreover, after the light was turned off the measured temperature didn't drop rapidly as it would if the thermocouple was heated by radiation. I still suspect that it was a result of a simple heat conduction. It is probably sufficient to touch the dome after the light is turned off to see that it becomes quite hot.


That's the inverse square law. A mm from the dome the intensity might only be 1/3 as much as actually touching the dome. And the temperature didn't drop rapidly because of the thermal mass of the probe. Yes, it may be a small mass, but it also is a very small surface area from which to conduct away heat in order to drop in temperature. Besides that, there is very poor thermal conductivity between the probe and dome, even if they are touching. There would still be a lot of tiny air gaps and such without thermal paste. Because of this, any rapid temperature increase the probe experiences when the emitter is turned on is primarily due to it absorbing emitted light. I'll grant that the dome rises somewhat above ambient as it's not perfectly transparent. But certainly not too hot to touch. If anyone has a non-contact IR thermometer then perhaps they can help here. Measure the temperature of the dome immediately after the LED has bee turned off. That will negate any possibility of errors just in case the IR thermometer responds to visible light. It shouldn't, but then again I've never used one.


----------



## wapkil (Dec 14, 2009)

jtr1962 said:


> Because of this, any rapid temperature increase the probe experiences when the emitter is turned on is primarily due to it absorbing emitted light. I'll grant that the dome rises somewhat above ambient as it's not perfectly transparent. But certainly not too hot to touch. If anyone has a non-contact IR thermometer then perhaps they can help here. Measure the temperature of the dome immediately after the LED has bee turned off. That will negate any possibility of errors just in case the IR thermometer responds to visible light. It shouldn't, but then again I've never used one.



Unfortunately I don't have an IR thermometer but I just tested a dome temperature of an MC-E LED driven with ~2.5A in a limited run L-mini II MC-E. After it ran for ~1 minute, I turned the light off, took a thermocouple showing the room temperature (22 deg. C) and touched it to the dome - it read ~50 deg. C. It took me around one second between turning off the light and touching the dome so the dome temperature was probably significantly higher immediately after the current was cut off...

EDIT: It also took some time before the thermocouple reading stopped rising. Obviously at the same time the dome temperature was falling, making the difference between the reading and the dome temperature when the light was on even higher.


----------



## jtr1962 (Dec 14, 2009)

Yes, the dome temperature probably fell a bit before the temperature stabilized, so perhaps it was 60° or 65°C when the LED was running. That actually sounds reasonable to me, and about in line with some of my other observations. For example, when I took an XR-E down to around -25°C with a thermoelectric module, the moisture condensing on the dome didn't freeze when the LED was running at 2+ amps, but did freeze when it was turned off. So the dome was probably 30°C or so higher in temperature than the heat sink. A smaller dome, being closer to the die, or a higher-powered LED with a large dome, like the MC-E you tested, would be higher in temperature still, perhaps as high as 65°-70°C at room temperature. This makes sense from a physical standpoint. Even if the dome only absorbs a few percent of the emitted energy, that's enough to heat it to those sorts of temperatures. But I wouldn't consider temperatures like this quite hot. I just ran a test on some P7s I had set up. I let them run a while, then shut them off and touched the dome. It's warm but not hot-I'd say maybe 50°-55°C. I can keep my finger on it indefinitely. However, if I keep my finger on the dome of one ( or just above it ) while it's turned on after about 20 seconds it's too hot to keep there. So it is indeed the radiation doing this heating, not the dome being too hot to touch. The instant I turn the LEDs off, my finger no longer feels hot. If the dome had been getting hot enough to burn my finger, then it would take a finite time for the burning sensation to go away as the dome gradually cooled.

What kind of temperatures do you get if you keep the probe on the dome and leave the LED on? I'd guess you'll be getting much higher temperatures.


----------



## MarineBeams (Dec 16, 2009)

I have been testing an oil filled light for the past 10 months. 3 cree R2's in a IP68 sealed acrylic enclosure running 24/7 @500ma. The light was 5 feet underwater in my canal the whole time. The oil was 100% mineral oil and it completely surrounded the heatsink (a very small and thin aluminum flat-stock, no fins).

My theory: 1. Constant fresh water would cool the oil filled housing much better than air ever could, and the cool oil would keep the lights happy. 2. the oil makes the unit less likely to crush at extreme depths. 3. Water could not enter unless oil was expelled, making leaks less likely and a very small bit of water intrusion would not equal immediate death to the electronics.

*The light just failed last week*. I haven't cracked it open yet but can see a serious black buildup on the solder points, shorting the gap. 

What I figure is that although the oil was 100% pure, impurities from the electronics and solder caused a slight electrolysis effect. Should have soaked them better with alcohol I guess.

I learned a lot from the experiment and have some idea's I may incorporate into another prototype.


----------



## jtr1962 (Dec 16, 2009)

MarineBeams said:


> I have been testing an oil filled light for the past 10 months. 3 cree R2's in a IP68 sealed acrylic enclosure running 24/7 @500ma. The light was 5 feet underwater in my canal the whole time. The oil was 100% mineral oil and it completely surrounded the heatsink (a very small and thin aluminum flat-stock, no fins).
> 
> My theory: 1. Constant fresh water would cool the oil filled housing much better than air ever could, and the cool oil would keep the lights happy. 2. the oil makes the unit less likely to crush at extreme depths. 3. Water could not enter unless oil was expelled, making leaks less likely and a very small bit of water intrusion would not equal immediate death to the electronics.
> 
> ...


Try clear epoxy next time instead of oil. Most liquids eventually get through the packages of electronic parts, causing them to fail. The epoxy will harden, protecting everything against moisture and pressure.


----------



## MarineBeams (Dec 16, 2009)

jtr1962 said:


> Try clear epoxy next time instead of oil. Most liquids eventually get through the packages of electronic parts, causing them to fail. The epoxy will harden, protecting everything against moisture and pressure.




That was my first choice, but finding a non-yellowing epoxy with no air bubbles and good (great) transparency was a stumbling block. If you know where to get some I will give it a try!


----------



## Daekar (Dec 16, 2009)

I was considering using mineral oil to create a non-conventional heatsink solution for modding a very old sheet-metal incan. While the spirit of the light moved me to lean in the direction of hotwire, I don't see why oil couldn't have helped in the absence of other heatsinking solutions, particularly when there was so much surface area to conduct to. Oil solutions seem to work extremely well for PC overclockers, too.... just immerse everything but the hard drive in mineral oil, hook up a remote radiator and pump, and they're good to go.

It is good to hear (although I'm sorry about its untimely demise) about possible stumbling-blocks revealed by your light, MarineBeams. I wonder if the combination of more thorough alcohol cleaning combined with a thin epoxy coating over most of the solder joints would prolong the lifespan of the system?

I don't think an oil-light is necessarily a good solution for all light designs and purposes, but in non-traditional designs it seems like something worth considering.


----------



## wapkil (Dec 16, 2009)

jtr1962 said:


> Yes, the dome temperature probably fell a bit before the temperature stabilized, so perhaps it was 60° or 65°C when the LED was running. That actually sounds reasonable to me, and about in line with some of my other observations. For example, when I took an XR-E down to around -25°C with a thermoelectric module, the moisture condensing on the dome didn't freeze when the LED was running at 2+ amps, but did freeze when it was turned off. So the dome was probably 30°C or so higher in temperature than the heat sink. A smaller dome, being closer to the die, or a higher-powered LED with a large dome, like the MC-E you tested, would be higher in temperature still, perhaps as high as 65°-70°C at room temperature. This makes sense from a physical standpoint. Even if the dome only absorbs a few percent of the emitted energy, that's enough to heat it to those sorts of temperatures. But I wouldn't consider temperatures like this quite hot. I just ran a test on some P7s I had set up. I let them run a while, then shut them off and touched the dome. It's warm but not hot-I'd say maybe 50°-55°C. I can keep my finger on it indefinitely. However, if I keep my finger on the dome of one ( or just above it ) while it's turned on after about 20 seconds it's too hot to keep there. So it is indeed the radiation doing this heating, not the dome being too hot to touch. The instant I turn the LEDs off, my finger no longer feels hot. If the dome had been getting hot enough to burn my finger, then it would take a finite time for the burning sensation to go away as the dome gradually cooled.
> 
> What kind of temperatures do you get if you keep the probe on the dome and leave the LED on? I'd guess you'll be getting much higher temperatures.



The temperatures I would get if I kept the probe on the dome would be something around 20-30 deg. C higher. I agree that the radiation can heat up the dome - all the radiation has to travel through it and probably a few percent is converted to heat. What I'm still not sure about is how much the radiation alone can rise the temperature of the thermocouple.

It's an interesting topic for me because the LED dome is frequently the only place on the LED that can be easily measured in an assembled flashlight. The question is, whether it can be used to estimate the junction temperature. 

When I was measuring the dome temperature in an MC-E LED powered with ~10W, the comparison to the junction temperature estimated from the theoretical junction temp./brightness relation suggested that the difference between the junction and the dome is only ~20 deg. C. It was surprising for me, because I believe there shouldn't be such a low resistance thermal path between the junction and the dome. 

Maybe the temperature rise due to the radiation absorbed by the dome can be the answer? It is also possible (although seemed unlikely to me) that the thermocouple doesn't show the actual dome temperature if it is indeed additionally heated by the radiation. I haven't investigated it further and I don't know the answers.


----------



## jtr1962 (Dec 17, 2009)

wapkil said:


> The temperatures I would get if I kept the probe on the dome would be something around 20-30 deg. C higher. I agree that the radiation can heat up the dome - all the radiation has to travel through it and probably a few percent is converted to heat. What I'm still not sure about is how much the radiation alone can rise the temperature of the thermocouple.


Radiation at the intensity existing at the dome can easily raise the temperature of the thermocouple 20 or 30 degrees C. Like I said, it's up to two orders of magnitude higher than full sunlight. We all know how being in the sun can raise the temperature of things above ambient. Same mechanism applies here.



> It's an interesting topic for me because the LED dome is frequently the only place on the LED that can be easily measured in an assembled flashlight. The question is, whether it can be used to estimate the junction temperature.


Interesting question, but I can tell you right now dome temperature and junction temperature are not really related.



> When I was measuring the dome temperature in an MC-E LED powered with ~10W, the comparison to the junction temperature estimated from the theoretical junction temp./brightness relation suggested that the difference between the junction and the dome is only ~20 deg. C. It was surprising for me, because I believe there shouldn't be such a low resistance thermal path between the junction and the dome.


There isn't a low resistance thermal path between the junction and dome. The primary mechanism through which the dome heats up is absorption of some of the LED's emitted light. If the dome were perfectly transparent then it would be more or less at ambient temperature, perhaps a few degrees above. The dome is thermally coupled to the LED case, but it's relatively poor coupling because the dome material is a poor thermal conductor relative to the other materials in the LED case ( usually alumina ceramic and copper pads ). It's sort of like if you put a piece of styrofoam insulation on a hot metal plate. You can easily touch the styrofoam even if the plate is 100°C. The LED dome isn't as insulative as styrofoam, but the same general idea applies here. It wouldn't be much warmer than ambient if it didn't absorb some light ( and it absorbs only a few percent at most ).



> Maybe the temperature rise due to the radiation absorbed by the dome can be the answer?


That is definitely the answer. It would be nice if there were some external way to measure junction temperature but unfortunately there isn't.


----------



## wapkil (Dec 17, 2009)

Thank you for the explanations. I'd have to check but I think that with 10W power even a few percent of the radiation absorbed may translate to a few hundred milliwats heating the dome.

Technically there has to be some relation between the junction and the dome temperature but it may be much too complicated to be useful. For example if it works as you described, in the same setup a lower junction temperature could lead to a higher emission and a higher dome temperature  

On the other hand, if in a particular setup this relation could be established, it could probably also be used to estimate the junction temperature, e.g. in my L-Mini measurements it seemed pretty consistent with theoretical temperature/brightness values. I'm not sure though if what I did there was completely correct - I'll have to add a link to this discussion in that thread.

BTW, do you know any better way of estimating the junction temperature in an assembled flashlight than measuring the changes in brightness?


----------



## jtr1962 (Dec 17, 2009)

MarineBeams said:


> That was my first choice, but finding a non-yellowing epoxy with no air bubbles and good (great) transparency was a stumbling block. If you know where to get some I will give it a try!


I haven't tried it yet, but this stuff looks pretty good.


----------



## Freeze_XJ (Dec 18, 2009)

Then still the heat transport would be low. Oil absorbs quite some heat, but sucks at transmitting it. To get effective cooling, you would want to circulate the stuff (completely impossible with epoxies), which isn't funny if we're talking oil. Just a little bit of flow tremendously increases cooling capabilities, but non-moving oil (or water, for that matter) is almost as horrible as air. 
Just for your referencing :
Conductivity of air : 0.024 (W/mK, Watt per meter per kelvin)
Aluminium : 250
Oil (olive) : 0.17
Oil (machine stuff) : 0.15
Glass : 1.05
source
So if you really want to have static oil : use glass instead. 
Or even better : make your entire substrate out of metal, and call it the anode  Isolate a small patch to the backside as kathode, and connect your anode to the outside of the light. Best conductivity you can possibly get.


----------



## JFD140 (Dec 18, 2009)

there is some secret trick to using the clear max clr... i returned the container i ordered because its damn near impossible to get all the air bubbles out of it. Which leaves you with a bubbly covering.
The epoxy also throws off the optics of the LEDs dramatically reducing brightness.


----------



## Illum (Dec 18, 2009)

Freeze_XJ said:


> Then still the heat transport would be low. Oil absorbs quite some heat, but sucks at transmitting it. To get effective cooling, you would want to circulate the stuff (completely impossible with epoxies), which isn't funny if we're talking oil. Just a little bit of flow tremendously increases cooling capabilities, but non-moving oil (or water, for that matter) is almost as horrible as air.



Considering there are miniature PC fans that are IP55 and IP21 rated it wouldn't necessarily be impossible to mount a fan in the "oil cell" and flood it with oil


----------



## kidsonp (Jul 16, 2012)

MarineBeams - have you got any further with your experiments of running an LED in oil? It' s been a while but i'm still interested.

Ta


----------



## Norm (Jul 17, 2012)

kidsonp said:


> MarineBeams - have you got any further with your experiments of running an LED in oil? It' s been a while but i'm still interested.
> 
> Ta



:welcome:

Unfortunately MarineBeams doesn't appear to have visited CPF in almost three years.

Norm


----------



## blasterman (Jul 17, 2012)

There was a liquid parafin cooled LED prototype being talked about awhile back.

Same problem - once you heat the liquid up, you then have to remove the heat from the liquid.


----------



## wquiles (Jul 17, 2012)

blasterman said:


> Same problem - once you heat the liquid up, you then have to remove the heat from the liquid.



+1

It is "always" the same problem. The more power in the LED, the more heat you have to remove (somehow).

The process is pretty much also always the same:
- LED heats up
- the LED efficiency drops, the output of the LED starts getting lower, 
- the vf lowers and the current goes up *(unless you have a current regulated power source)
- thermal energy travels directly or via MCPCB to heatsink
- heatsink heats up
- thermal energy travels from heatsink to body or head of light

-> at this point only you now have just two ways to transfer heat outside of the body:
- the poor transfer from body to the external air
- to the blood of the person holding the light

Either way, as the LED keeps running, the system (flashlight by itself in air, or flashlight in the users' hand) will reach a steady state temperature.

The higher the power being fed to the LED and the smaller the host, the quicker the person holding it will find the host too hot to handle comfortably for long periods of time. The larger the host, the longer it takes for this to happen, plus there is more surface area to help dissipate some of the heat (but again, thermal transfer to air is terrible as air is a good thermal insulator).

NOTE: The thermal resistance at the various junctions delays the transfer of heat, but the thermal energy still needs to travel and be dissipated (somehow). Yes, Copper is more efficient, but you are just moving it quicker to the body - Copper is not somehow "eliminating" the heat - it still needs to be dissipated (somehow). So it maters not if you have Al, Copper, fluid, etc.. - the amount of energy that needs to be moved is "still" the same. You are just delaying the steady-state system temperature.

Will


----------



## Walterk (Jul 17, 2012)

wquiles said:


> ....you are just moving it quicker to the body ....You are just delaying the steady-state system temperature.



Heat travelling faster makes more heat leave the room to make space for new heat from the led, that's heat flux. 
 At first it shows by the time when the systems arrives at the steady state temperature,
and at second it shows by having a higher or lower steady state temperature.


----------



## wquiles (Jul 17, 2012)

Walterk said:


> Heat travelling faster makes more heat leave the room to make space for new heat from the led, that's heat flux.


Yes, lower thermal transfer makes for a more efficient system. And we should always try to have as good thermal transfer as possible.

The problem is that now-a-days, in our eternal quest for "more power", the LED's is releasing significantly more heat than what the body/light can remove - that is precisely why the temperature of the body/light keeps increasing with time and why the efficiency/lumen output drops. Once you are in a situation where you are generating more heat than what the body can dissipate, the material used is no longer the important factor - the more critical factor is the surface area of the light. Since our flashlights have a fixed surface area, then we have an intrinsic limitation: the smaller the body, the hotter it's steady state temperature will be (assuming the LED is being driven at the same levels).

In the best case scenario, the blood of the person holding the light "is" the cooling system, unless:
- you are moving in air (such as in the case of a bike light housing with fins while the bike is moving). Here the effect is that of having a "fan" blowing colder air over the surface of the light. Of course when you stop moving, the temperature of the housing/body will go up again ...

or

- you are using the light under water (like in diving). Under water, the water surrounding the body/light can remove heat from the light much more efficiently than air or even the hand holding. Since for all practical purposes the thermal capacity of the water when diving is infinite (at least relatively to the puny power in a high power LED), the equilibrium point will give a significantly lower steady state temperature than outside of the water. The water basically helps us a lot to remove heat from the body/light much more efficiently.


Those of us old enough in the forum remember one of the very first LED lights from Surefire (L4 I think it was called): that tiny SureFire CR123 body used a 5 Watt Luxeon LED (on a star, thermally attached to the head which was also the heatsink - all one piece). You could not hold it in your hands after 3-4 minutes. I even remember creating a post here in the forum and asking if it was "normal" 

And even today, with my Titanium Sunwayman V10R (again, a fairly small body), when using a 4.2V LiIon cell driving a 3watt Nichia 219 LED - if I leave it on a desk on HIGH for just a couple of minutes, it becomes "very" uncomfortable when I go grab it (and forget I left it on HIGH!).

Will


----------



## saabluster (Jul 18, 2012)

wquiles said:


> Since our flashlights have a fixed surface area, then we have an intrinsic limitation: the smaller the body, the hotter it's steady state temperature will be (assuming the LED is being driven at the same levels).


I don't have time right now for in-depth responses but I have to say that this is not true. You can engineer around this. Just takes a little out-of-the-box thinking.


----------



## Th232 (Jul 18, 2012)

saabluster said:


> I don't have time right now for in-depth responses but I have to say that this is not true. You can engineer around this. Just takes a little out-of-the-box thinking.



Active cooling?


----------



## saabluster (Jul 18, 2012)

Th232 said:


> Active cooling?


That's one. There is one other way though. Passive to boot.


----------



## RoGuE_StreaK (Jul 18, 2012)

Active finning - think porcupine! 

As things are going a little sideways here anyway, anyone know where to get small cheap fans for active cooling, say in the order of 25mm? Cheapest I've found have been one-off buys for $5+ each.
If I knew more about driving piezos, I'd try to engineer a piezo air pump - those suckers are expensive!


----------



## wquiles (Jul 18, 2012)

saabluster said:


> That's one. There is one other way though. Passive to boot.



That would be cool. The more efficient we can make things the better 

Will


----------



## Steve K (Jul 18, 2012)

wquiles said:


> .... Since our flashlights have a fixed surface area, then we have an intrinsic limitation: the smaller the body, the hotter it's steady state temperature will be (assuming the LED is being driven at the same levels).
> .....



I think I'd argue about the "fixed surface area" part of the statement. It's likely that there are practical limitations, since few people want to carry a flashlight the size of a baseball bat. Heatsink fins can be engineered to provide quite a bit of surface area, albeit at the cost of ruggedness and manufacturing expense. Adding a small fan is another solution, with obvious disadvantages. 

In a lot of ways, it's similar to the problems of getting heat out of laptops. Ultimately, the most desirable solution is to get a CPU or LED with higher efficiency, thereby reducing the need to dump heat while improving battery life (or reducing battery size). 

The development of LEDs that can run at 85C offer some advantages. I can see that they make design easier for fixed lighting (inside of buildings). I haven't run the numbers to see if it would help with flashlights, unless people are willing to wear oven mitts when using their flashlight. 

Steve K.


----------



## blasterman (Jul 18, 2012)

Back to the liquid thing............I'm pretty sure aluminum or copper has orders of magnitude better thermal conductivity than most liquids, excluding some weird things like mercury. So, I would guess that if you immersed a star mounted emitter like an XP-G or XM-L in liquid, and hit it with enough current, you'd likely boil the liquid and quickly kill the emitter. Also going by the chart (below) regular water has better thermal conductivity than paraffin, or any petroleum based liquid for that matter. 

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

Flashlights share a lot of the same thermal problems that standard light bulb retrofits have, and the solution in both cases seems to not deviate much from a standard cylinder. A big difference though is LED light bulb retrofits, and even higher end fixtures tend to use lots of 1watt and smaller LED's to help spread the load. 

Obviously adding fins helps with convection area, but the positive thermal effect of fins limits very quickly in a passive cooled environment. Plus, the fins need to be thick and preferably radiate from the entire surface area of the immediate slug or plate catching the initial heat. Not sure why custom flashlights can't be CNC'd with thicker and broad fins immediatley behind the LED slug (??) or is it an aethestic thing?


----------



## AnAppleSnail (Jul 18, 2012)

Passive cooling fins are quite different from what you guys are envisioning. For the most part, a passive heatsink cools by conduction/convection to air and radiation to things.

1. Heat air. The air is then at the flashlight temperature and cannot absorb more heat, until... that air rises away, drawing in cooler air. This requires open air, much like a tailstand on a tabletop. Conventional design includes stubby fins with the vanes pointed 'up' in normal orientation. Unconventional design would be a hyperboloid tower.

2. Radiation. Radiation cools directly to surrounding surfaces, and is mostly based on (Tlight - T(walls, floor, ceiling, sky)). Fins DO NOT help with radiation, except to increase the diameter of the radiator. Radiating is, well, radial. Fins sticking out face each other and cannot radiate to each other, so radiating heat is best done by a few long vanes. Conventional design includes high-emissivity coatings (Black anodize, copper, etc), 'bold' cooling features (Big cooling ribs, etc). Unconventional design would be to attach a matte-black half-inch-thick plate to a flashlight's heat rejection.

Passive cooling without the help of a hand is limited by heat rejection. This is mostly improved by:

More conduction to air (Higher surface temperature)
More radiation to air (Higher emissivity)
More conduction to non-air things (Hand, water, fans)


----------



## AnAppleSnail (Jul 18, 2012)

blasterman said:


> Back to the liquid thing............I'm pretty sure aluminum or copper has orders of magnitude better thermal conductivity than most liquids, excluding some weird things like mercury. So, I would guess that if you immersed a star mounted emitter like an XP-G or XM-L in liquid, and hit it with enough current, you'd likely boil the liquid and quickly kill the emitter. Also going by the chart (below) regular water has better thermal conductivity than paraffin, or any petroleum based liquid for that matter.


Paraffin coolers don't work quite that way. Consider an ice flashlight, 300 joules per gram of melt. If I want a flashlight to run for (t) seconds at (W) power, I can plan on a safe thermal load. But the ice heat-sink (A true heatsink, not a block of metal that absorbs some heat and radiates it) will NOT give me great runtime - it's only for sprints.

Suppose I modify my Torchlab H3 triple with 30cc of ice (About 1 fluid ounce). When it has sat in a freezer overnight, this gives me (300*30) joules of melting before the flashlight reaches 1 degrees C. That is 9000 watt*seconds of heat that can be absorbed - or I can run it at (3.7v * 4.5A) = 15W for (9000/15) about 10 minutes before the ice will all melt.

These paraffins are chosen for practical melting points. They may melt at 50C, with a lower heat of fusion - so that in peak running the heat is absorbed to be released later.


----------



## deadrx7conv (Jul 18, 2012)

Liquid cooling isn't too feasible for small or handheld lights. Its not worth even talking about it. For thought, research sodium filled engine valves and CPU heat pipes. But, I do notice that the head of my flashlight is seriously hotter than the tail. So, if there is a way to move the heat across the entire flashlight, we might benefit with longer run times before not being able to handle the flashlight. 

Where liquid 'centralized' cooling would benefit is either multiple lights, or very high power lighting, when neither have a surplus of heat sinking area either due to a lack of space, or by trying to make the light visually appealing. 

A tiny heat sink with coolant tubes might be easier to integrate into wall/ceiling lighting. Can you picture a single small fan cooled rooftop radiator with a loop of antifreeze:water running to:fro all LED ceiling/wall/floor fixtures? No more worrying about trying to hide those 5lb aluminum finned heat sinks in your interior decorations!

Another example would be a 100w LED mounted on a 1/2" pole. Would you want the basketball sized aluminum finned heat-sink on the top of the pole? Or, tuck a couple cooling lines up the internals of the pole with a radiator/sump/pump mounted elsewhere. The thought of multiple 8000 lumen lights, with no noticeable heat sinks, across a large yard, mounted remotely or on small diameter poles, could be interesting for someone. 

No bugs to work out. There are plenty of CPU liquid cooling solutions. There are plenty of automotive type cooling(antifreeze/oil/ATF/PSF...) And, many houses have run radiant or forced hot water type heating systems for years. You'll just need competence to make it leak and sweat proof. 

So, whatever happened to Switch Lighting and EternaLeds Hydralux?


----------



## blasterman (Jul 18, 2012)

> Paraffin coolers don't work quite that way. Consider an ice flashlight, 300 joules per gram of melt.


I think we're talking about two different applications. I was referring to LED retrofits like those below that use liquid filled capsules that do *something*, but we're not sure what it is:

http://www.switchlightingco.com/
http://www.candlepowerforums.com/vb...-LED-Globe-A-Shape-Bulb-Eternaleds-HydraLux-4

The idea of using state-change to absorb heat in short run applications sounds totally feasible to me. Anybody who's taken HS chemistry understands how this works when you graphed the amount of energy it took to melt ice, or wax, or mothballs, etc. The one caveat I would though, and I'm sure you've thought of it, is once you converted the solid to a liquid you would then have to wait longer for the now liquid to realease it's energy and resume a solid state -vs- using a conventional design.



> Fins DO NOT help with radiation, except to increase the diameter of the radiator



Not entirely true....even in a vacuum fins aid in radiating thermal energy away from the source. Best example is cooling fins on the RPG used by space probes. But yeah, I get what you're saying and agree. I'm constantly telling people to avoid high performance CPU coolers for passive cooling Bridgelux because the thin and dense fin arrangements actually trap more heat than short, stubby ones. For flashlights though my visual would be a wide collar of thick fins radiating with a square length to height ratio around the LED contact area. This is very similiar to some LED retrofits and 1watt laser pointers I'm seeing. This allows you to use both convection and hand thermal transfer. While a stationary flashlight obviously has the convection problems you mentioned the reality is that most of the time you're moving a flashlight around, etc. Not sure if the fins would yield a 1% improvement or 20% improvement, but at worse it's extra mass to absorb heat.

What would be really cool is if you were able to use carbon fin heat piping on a flashlight, and then polish it.


----------



## idleprocess (Jul 18, 2012)

saabluster said:


> That's one. There is one other way though. Passive to boot.


Clever use of a heat pipe comes to mind - helps move the heat away faster than sinking it into a block of metal - but only achieves so much.



deadrx7conv said:


> Where liquid 'centralized' cooling would benefit is either multiple lights, or very high power lighting, when neither have a surplus of heat sinking area either due to a lack of space, or by trying to make the light visually appealing.
> 
> A tiny heat sink with coolant tubes might be easier to integrate into wall/ceiling lighting. Can you picture a single small fan cooled rooftop radiator with a loop of antifreeze:water running to:fro all LED ceiling/wall/floor fixtures? No more worrying about trying to hide those 5lb aluminum finned heat sinks in your interior decorations!


This has occurred to me as well, although I suspect it would not be practical on the small scale of most residential / commercial arrangements where fixture size isn't a problem so long as the per-fixture power is reasonable. Hobbyists will likely just use a fan if heat removal / sink limitations are real issue ... commercial applications will use highly-engineered thermal design.

Worked really well for the flying searchlight, albeit the fluid seemed largely to be for speed of heat removal and aerodynamic convenience.



deadrx7conv said:


> So, whatever happened to Switch Lighting and EternaLeds Hydralux?


I barely remember Hydralux ... Switch Lighting is going on 12 months past their original estimate on retail availability, although they seem a great deal more serious about launching a generally-available product.


----------



## saabluster (Jul 18, 2012)

idleprocess said:


> Clever use of a heat pipe comes to mind - helps move the heat away faster than sinking it into a block of metal - but only achieves so much.


OK. So you have the implement. Now what is the implementation? Sorry if I'm being coy. Just trying to stimulate the minds here rather than just blurt something out. Although it is true that what I am referring to "only achieves so much"(that applies to pretty much everything) it achieves much more than what I think you are thinking.


----------



## Th232 (Jul 19, 2012)

Heatpipe stretching to the other end of the flashlight, normally the coolest part? That will help evenly distribute heat instead of having some kind of a thermal gradient from one end to another (how steep that gradient is to begin with is another question). That combined with finning the entire body would be interesting to see, as would holding it. Assuming you've designed the fins correctly and with enough space around them. Might actually end up more like a pin type heatsink than one with fins.

I've never seen a flashlight where the body was completely finned. Maybe it should be called the Porcupine.


----------



## RoGuE_StreaK (Jul 19, 2012)

I'd previously investigated doing that (heatpiping along the body to the rear), but couldn't find much info on DIY-level heatpipe construction; the wicking materials, and somehow filling and sealing the pipes under vacuum seemed beyond reach. But if I'm more than happy to be shown a way!
My latest redesigns have quite extensive finning, will have to finish them off to see how they affect machining costs - not to mention whether it'll actually _do_ anything...


----------



## MikeAusC (Jul 19, 2012)

Heat pipes are so cheap there isn't much point trying to match the performance of wick-lined Heat Pipes. Try Element 14 or Farnell.


----------



## idleprocess (Jul 19, 2012)

saabluster said:


> OK. So you have the implement. Now what is the implementation? Sorry if I'm being coy. Just trying to stimulate the minds here rather than just blurt something out. Although it is true that what I am referring to "only achieves so much"(that applies to pretty much everything) it achieves much more than what I think you are thinking.



That's about as far as the thought went ... expertise in thermodynamics is something I lack.

My thinking was that even in situations where you have a massive heatsink, the heat will only travel so far - as many have witnessed with C/D maglite mods where only the head of the flashlight gets appreciably hot while the tail might be close to room temperature. 'Seems that if you were to transport that heat faster ala the phase change that heat pipes allow for, you could realize more utilization of your heat sink's mass and surface area.

As far as implementation ... not so sure. Simplest seems to have an interface to another heatsink in the tail, although clever implementation could perhaps use the heatpipe more like a passive radiator, with the heat dumped periodically along its length as opposed to at its terminus (my ignorance comes into play here - I don't know if they can be made to work this way). Another thought was some triple-walled battery tube arrangement - where the battery tube itself acts as the heat pipe - but that would be tricky to execute and likely troublesome since it would contain the fluid within a thin-walled construct that's also a structural part.


----------



## saabluster (Jul 20, 2012)

Th232 said:


> Heatpipe stretching to the other end of the flashlight, normally the coolest part?


Although this idea does have merit it is not exactly out of the box. That is the obvious solution but ultimately not the best when trying to combine super high current in a small package without burning the user's hand. In fact it may, at certain current levels, do quite the opposite. 



idleprocess said:


> That's about as far as the thought went ... expertise in thermodynamics is something I lack.
> 
> My thinking was that even in situations where you have a massive heatsink, the heat will only travel so far - as many have witnessed with C/D maglite mods where only the head of the flashlight gets appreciably hot while the tail might be close to room temperature. 'Seems that if you were to transport that heat faster ala the phase change that heat pipes allow for, you could realize more utilization of your heat sink's mass and surface area.
> 
> As far as implementation ... not so sure. Simplest seems to have an interface to another heatsink in the tail, although clever implementation could perhaps use the heatpipe more like a passive radiator, with the heat dumped periodically along its length as opposed to at its terminus (my ignorance comes into play here - I don't know if they can be made to work this way). Another thought was some triple-walled battery tube arrangement - where the battery tube itself acts as the heat pipe - but that would be tricky to execute and likely troublesome since it would contain the fluid within a thin-walled construct that's also a structural part.



Well I don't consider myself an expert in thermodynamics either. I have done a lot of thinking and testing in that area though. At least as it relates to flashlights. The conclusion? That a great many lights today are being designed all wrong. There are two instances where you need to reconsider traditional flashlight design. 1When flux density reaches a level that the heat from steady state operation rises above comfortable user tolerance. 2. When creating a larger sized light but still want the flashlight form-factor. 

Case in point. The Olight SR90. Now this is just my opinion mind you, but I think that light reeks of poor design. All they did was take a normal flashlight and hit 300% enlarge on their printer and call it a day. The result is a bloated beast. The scaling-up process of the traditional form-factor only works so far. At a certain point you have to rethink it. 

The solution is something I call a "thermally decoupled heatsink". Instead of the whole flashlight being the heatsink only a small portion in my design is used for heatsinking. Even if the rest of the light is metal the heatsink is thermally insulated from it. Normally this would be a bad thing. In fact there are a few lights out there that by default have what appears to be a similar idea but when you scratch the surface a little more you will see that this idea is a bit more novel. At least in the flashlight world. Some lights are made primarily of plastic and so to get rid of heat they add a little heatsink. The end result is completely the opposite of what I am talking about though. They actually have to _reduce_ power with this design and here I am talking about _increasing_ power. 

The key is to use a heatsink that in and of itself is a phase change device. It would rely not on heat conduction to a hand but radiation and convection. The higher the temperature difference between the heatsink and ambient the more heat can be disposed of and the more efficient these forms of moving heat become. The key of course is to do this while keeping junction temps down. Which is why the use of a phase change element is absolutely crucial to the design. I won't get into all the specifics of my design but I assure you this idea is not pie-in-the-sky and that it does indeed work. I don't have the resources to commercialize it but if Surefire or the like want to get with me we can make some magic happen.


----------



## idleprocess (Jul 20, 2012)

saabluster said:


> The key is to use a heatsink that in and of itself is a phase change device. It would rely not on heat conduction to a hand but radiation and convection. The higher the temperature difference between the heatsink and ambient the more heat can be disposed of and the more efficient these forms of moving heat become. The key of course is to do this while keeping junction temps down. Which is why the use of a phase change element is absolutely crucial to the design. I won't get into all the specifics of my design but I assure you this idea is not pie-in-the-sky and that it does indeed work. I don't have the resources to commercialize it but if Surefire or the like want to get with me we can make some magic happen.



I'm going to guess that this is a considerably more involved than heat pipes and a remote heatsink.

I know the feeling on ideas that you can't develop - got a few myself that would require a bit of proving out and considerable patent research before I could consider trying to monetize them.


_EDIT_: OK, so I need to read more carefully ... heatsink *itself* is a phase-change device. Sounds a bit more elegant than running heat pipes to auxiliary heatsinks. But I'm drawing a blank on how this is going to passively remove world-beating amounts of heat. But maybe that's why it's sufficiently novel as to be worth licensing to industry.


----------



## SemiMan (Jul 21, 2012)

Phase change heat transfer for LED has been bandied about for some time. Hopefully you have something new as you are likely to run into patent issues. This one alone goes back to 2000

http://patft.uspto.gov/netacgi/nph-...&f=G&l=50&d=PALL&RefSrch=yes&Query=PN/6452217

Semiman


----------



## saabluster (Jul 21, 2012)

SemiMan said:


> Phase change heat transfer for LED has been bandied about for some time. Hopefully you have something new as you are likely to run into patent issues. This one alone goes back to 2000
> 
> http://patft.uspto.gov/netacgi/nph-...&f=G&l=50&d=PALL&RefSrch=yes&Query=PN/6452217
> 
> Semiman



Yes of course they have been both talked about and used in lighting systems for years. The patent you linked does not cover what I have. Not exactly anyway. Although it clearly mentions using a phase change device with lighting. But then so do a million other patents. I certainly wouldn't be surprised if some patent somewhere did cover it with as broad a stroke as they brush in those patents. What I am talking about doing goes a couple steps further than anything I have seen although admittedly I have not scoured the patents to see what prior art is out there.


----------



## bshanahan14rulz (Jul 23, 2012)

I'm currently working on a phase change / liquid heat exchange system whereby the end user bolts the copper MCPCB directly to the biological substructure of the frontal cranium. At low current levels, the inherent fluid in the bone isolation layer directly below the MCPCB will wick heat away from the LED, while at higher currents, certain volatile components within this inherently present and circulating liquid will vaporize. These volatile components' levels may be tweaked by the user, by indirectly introducing a solution of ethanol into the system. There are a few setbacks, such as runtime, that need to be addressed. The test subjects ran out of the heat exchange fluid because of imperfect connections when puncturing the bone isolation layer with the screws.


----------



## saabluster (Jul 23, 2012)

bshanahan14rulz said:


> I'm currently working on a phase change / liquid heat exchange system whereby the end user bolts the copper MCPCB directly to the biological substructure of the frontal cranium. At low current levels, the inherent fluid in the bone isolation layer directly below the MCPCB will wick heat away from the LED, while at higher currents, certain volatile components within this inherently present and circulating liquid will vaporize. These volatile components' levels may be tweaked by the user, by indirectly introducing a solution of ethanol into the system. There are a few setbacks, such as runtime, that need to be addressed. The test subjects ran out of the heat exchange fluid because of imperfect connections when puncturing the bone isolation layer with the screws.



That's awesome. You might try incorporating a closed-loop condenser into the system. That should up the runtime considerably.


----------

