Oil cooled LED

[marcopolo]

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]

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]

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]

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]

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]

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]

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]

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

 

[Roger Sully]

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]

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

Semiman

 

[blasterman]

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]

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.

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.

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]

Oh here we go, hydralux.

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

CPF thread.

 

[marcopolo]

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]

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]

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]

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]

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]

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]

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?