# Interesting passive liquid cooled LED bulb



## liveforphysics (Sep 18, 2009)

Many of the incan LED replacement bulbs are limited by the ability to reject heat. This product offers a unique solution, and uses the liquid as an optical transmission medium to minimize optical loss. Much like the gel under the dome of the Cree LEDs. 

Larger sizes with perhaps 9 of the XP-G series leds could make for a very practical bulb for household lighting . 

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

Enjoy!
-Luke

PS: Sorry if this is a repost! I didn't find anything when I searched.


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## clint357 (Sep 18, 2009)

I've wondered how well water would transfer heat instead of solid aluminum or copper. I know the thermal conductivity of water is quite low, but I believe that is for still water, not taking into account the natural movement that occurs between warm and cool areas.


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## qwertyydude (Sep 18, 2009)

Unless there was a way to dissipate the heat all that will happen is the water takes a long time to get hot. Passively oil cooled computers face the same problem, the oil prevents hotspots but without a radiator you end up with a tub of really hot oil, takes a long time to heat up but it will heat up, same will be with this bulb. And the round outside does not offer much surface area to radiate the heat, you're better off with a very high surface area heatsink and an active fan, you can easily put a silent fan that doesn't move much air but with a lot of surface area the heat will easily dissipate. I can easily push about 1.4 amps through my led spotlight since it has a solid copper heatsink with a small fan and I don't get any angry blue led and the heatsink stays almost ambient temperature.


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## xenonk (Sep 19, 2009)

> When the light emitted by the light source module penetrates through the liquid, it is diffused to spread the lighting angle, and the total reflection between the liquid and the container may have light focusing effect and increase the brightness.


Wait, what?


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## liveforphysics (Sep 19, 2009)

The cooling advantage comes not from the increased specific heat*mass of the fluid, but rather in the ability to reduce the delta-T between LED die and the outside of the bulb being exposed to the air surrounding the bulb envelope. Exposing the LED directly to the air around it does the same thing of course, but this does it with an increase in surface area of perhaps 100-200x.


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## Chongker (Sep 19, 2009)

qwertyydude said:


> Unless there was a way to dissipate the heat all that will happen is the water takes a long time to get hot. Passively oil cooled computers face the same problem, the oil prevents hotspots but without a radiator you end up with a tub of really hot oil, takes a long time to heat up but it will heat up, same will be with this bulb. And the round outside does not offer much surface area to radiate the heat, you're better off with a very high surface area heatsink and an active fan, you can easily put a silent fan that doesn't move much air but with a lot of surface area the heat will easily dissipate. I can easily push about 1.4 amps through my led spotlight since it has a solid copper heatsink with a small fan and I don't get any angry blue led and the heatsink stays almost ambient temperature.


 


Yes, but this set-up would go against the whole purpose of the module, to act as a viable low consumption light source. Having active cooling such as with a fan would probably greatly increase the price of the module, and also, any gains over incandescents for efficiency in the LED itself would be diminished by the energy used to power the fan. This really seems like a neat, innovative idea to make a simple (maybe cheap) non-flourescent high efficiency lamp module.


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## Mr_Light (Sep 19, 2009)

If you search on hydralux you will find the other threads on this subject.


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## LEDninja (Sep 19, 2009)

Mr_Light said:


> If you search on hydralux you will find the other threads on this subject.


https://www.candlepowerforums.com/threads/236844
https://www.candlepowerforums.com/threads/237368

BTW
It uses Parafin Oil as the liquid.
Not water which would would cause a short circuit.


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## qwertyydude (Sep 19, 2009)

liveforphysics said:


> The cooling advantage comes not from the increased specific heat*mass of the fluid, but rather in the ability to reduce the delta-T between LED die and the outside of the bulb being exposed to the air surrounding the bulb envelope. Exposing the LED directly to the air around it does the same thing of course, but this does it with an increase in surface area of perhaps 100-200x.



Only problem there is the die doesn't directly contact the cooling fluid. It will still have to go through the silicone blob and possibly the glass lens covering it if it's a cree. Whereas traditional cooling pulls the heat out through the back of the led where there is a direct heat path to a heatsink. This makes more sense so yes as I've said it will eliminate hotspots but you'll still need a way to get rid of the heat and a round sealed plastic bulb will not do it. The computer in an aquarium that I've read about eventually got up to about 160F which is pretty much the junction temperature of the processor, and that's when the processor starts climbing in temperature even higher. And I imagine the bulb will get to the same situation without a proper cooling system for the liquid.


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## gadget_lover (Sep 19, 2009)

The other problem (once the heat gets out of the bulb) is the lack of air circulation in many lamp designs. Your typical funnel shaped desk lamp has small ventilation holes in the top to let air through, but the air surrounding the bulb and socket is still very hot. If you want to dissipate 10 watts of heat, you generally need air or fluid movement.

The point is... the liquid (oil, in this case) does not make heat disappear, it just moves it around. The heat stays in the bulb until it is moved to the air touching the bulb (directly or via a light fixture). 

While the oil is a neat gimmick, the difficulties of creating a bulb with integrated heat sink is greatly exaggerated.

Daniel


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## BentHeadTX (Sep 20, 2009)

The oil stabilizes the temperature across much more mass
The heat goes to the socket base as a direct connection
Heat naturally rises and draws in cooling air from the bottom

We are talking 4 watts! Consider that at least half a watt is going to be directly converted to light, that is 3.5 watts of heat that needs to go out of the thing. Old CPUs back in the 386 days would dump that level of heat and they lived. My dual core Atom processor has a passive heat sink that is very small and I would say the oil cooled light bulb probably has much more area. 

I'll get one of those bulbs once I know the XR-G LED is inside


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## qwertyydude (Sep 21, 2009)

Don't be too amazed at the heatsink on your atom processor. The atom processor is a new generation of ultra low power processors. The single core is only 4 watts dual core is only 8 watts and you'll still need a fan in your computer to keep the air moving to cool the processor much like the light bulb would be more compact with a fan rather than hoping a bulk of fluid will transfer enough heat to a small heatsink junction base or to the surface of the bulb.


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## blasterman (Sep 21, 2009)

> the difficulties of creating a bulb with integrated heat sink is greatly exaggerated.


 

Somewhat.

The real issue is trying to find the most efficient way to radiate heat from the conventional form factor that LEDs bulbs like this are trying to fit into.

The liquid isn't exactly a 'gimmick', but it doesn't fix the issue that you need to get read of the heat you create and all the liquid does is transport it. When it comes to heatsinks, thermal resistance is thermal resistance. Using liquid parafin or heat pipes or unobtanium for that matter doesn't get around the fact you need to get rid of the heat you are creating. If you work it backwards, and start with a requirement for 1000-800 lumens of light, there's no way you're going to reach it in this form factor without either active cooling or a monster heat-sink.
Or, we can wait for LEDs to hit 300 lumens per watt efficiency.

It's a 4-watt LED bulb, which means it's yet another over-priced gimmick to produce near *useless* levels of light. I also fail to see the real innovation of 360 degree light. Using three LEDs in a triangle does the same thing.


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