Flashlight's head filled with fluid!

[okarina]

Hi!

I was thinkin about to make an LED flashlight, and fill the head with fluid, especially Glycerin!

The reasons:
1. For better cooling
2. For better light output

Glycerin has nearly the same refraction index like glass. http://www.youtube.com/watch?v=anJuZdL_vsw
So if you fill the head with glycerin, the LED's dome, the front glass and the space between these(which is now filled with glycerin) will act like one big glass.

Why doesn't anyone tried this yet?

 

[John_Galt]

Waterproofing the elctronics/sealing the head from everything else can be an issue. Also, it makes the head heavy, potentially unbalancing the light (though to be fair, many high output lights have pretty heavy battery compartments).

Also, the reflectors may be damaged by the liquid in the head, and filling the head w/o air bubbles could be problematic...

Off topic... Isn't glycerin explosive (as in nitro-glycerin)?

 

[Lynx_Arc]

sounds easy but probably isn't. first you have to have better seals that normal to keep the liquid in. second you have to make sure nothing inside the head will combine with the liquid or create debris that would float around inside of it. third the cooling on LEDs are mostly at the back plates which are heatsinked to the body of the light and if this is done properly the heat is already transferred to the case and uses the air inside the head to dissipate heat and your hand and outside air. I don't see this adding much heat transfer and could be a possible mess if you were to drop the light and damage a seal. Also air tends to transmits light better than liquids so in effect you are actually reducing output slightly by inserting it between the LED and lens.

 

[Mnementh]

Why doesn't anyone tried this yet?

Probably because they read the MSDS sheet.

From the MSDS:
Special Remarks on Reactivity:
Hygroscopic.
Glycerin is incompatible with strong oxidizers such as chromium trioxide, potassium chlorate, or potassium
permanganate.
Glycerin may react violently with acetic anhydride, aniline and nitrobenzene, chromic oxide, lead oxide and fluorine,
phosphorous triiodide, ethylene oxide and heat, silver perchlorate, sodium peroxide, sodium hydride.

I'm not sure about the rest of that, but chromium trioxide is used in chrome plating. Having NO idea how reflectors are made, nor what their made of, I'd recommend finding out before filling the head of the flashlight with Glycerin. A google search did bring up a link of using it on LED flashlight reflectors.

Also, how much heat is given off by the LED? Glycerin has a flash-point in a closed cup of 160C.

 

[okarina]

Waterproofing the elctronics/sealing the head from everything else can be an issue. Also, it makes the head heavy, potentially unbalancing the light (though to be fair, many high output lights have pretty heavy battery compartments).

Also, the reflectors may be damaged by the liquid in the head, and filling the head w/o air bubbles could be problematic...

Off topic... Isn't glycerin explosive (as in nitro-glycerin)?

Does Glycerin conduct electricity?

Okay, if it's conduct, do it with Cedar oil. It has near the glass refraction index too and it's dielectric, but I think glycerin is that too. Somebody may tell us.

Many computer modders use oil cooling. They fill the whole, I say whole computer with oil.

I think it won't be any chemical reaction, so it won't damage the reflector and the LED.

You right, Nitro-Glycerin is explosive, but glycerin isn't. It's in soap and many cosmetics.

When you assemble the light, you fill it, with a hypodermic syringe and you close the head with something like glue, I don't know.

What do you think?

 

[John_Galt]

Isn't water the best thing for cooling, though? Why "oil" cooling? I'm assuming because it doesn't conduct electricity.

And, as Lynx_Arc pointed out, LED's are mostly cooled through the back plate. Realistically, I think filling the head with fluid would do nothing but increase the complexity of construction, and ruin any balance, as well as reducing output (even slightly). Time and energy would probably be better spent figuring out how to add more heatsinking (either through increased thermal mass, or increased surface area) to your light.

We had a thread on a similar topic a long while ago, but IIRC, it didn't work out very well: was extremely complicated...

 

[okarina]

sounds easy but probably isn't. first you have to have better seals that normal to keep the liquid in. second you have to make sure nothing inside the head will combine with the liquid or create debris that would float around inside of it. third the cooling on LEDs are mostly at the back plates which are heatsinked to the body of the light and if this is done properly the heat is already transferred to the case and uses the air inside the head to dissipate heat and your hand and outside air. I don't see this adding much heat transfer and could be a possible mess if you were to drop the light and damage a seal. Also air tends to transmits light better than liquids so in effect you are actually reducing output slightly by inserting it between the LED and lens.

If you put an LED flashlight close to your face, you can feel that it emits heat, and then you can be sure, it can be heated in the front.

Okay, air transmits light better, it's true. But! The light comes out from the emitter. And it goes through 3 materials. The LED's dome, the air and the front glass. So much of the light is blocked.
When you fill it with a glycerin or cedar oil, it will act like a big glass or a big dome on the LED. These fluid also removes the litle scratches and bumps on the LED's dome.

 

[John_Galt]

If you put an LED flashlight close to your face, you can feel that it emits heat, and then you can be sure, it can be heated in the front.

Okay, air transmits light better, it's true. But! The light comes out from the emitter. And it goes through 3 materials. The LED's dome, the air and the front glass. So much of the light is blocked.
When you fill it with a glycerin or cedar oil, it will act like a big glass or a big dome on the LED. These fluid also removes the litle scratches and bumps on the LED's dome.

Well, yes, the photons hitting your skin, and the glass (or polymer) dome and glass/plastic lens will be in enough quantities that some will be turned into thermal energy. LED's may also emit some slight amount of infra-red wavelength (but probably not much).

 

[okarina]

Isn't water the best thing for cooling, though? Why "oil" cooling? I'm assuming because it doesn't conduct electricity.

And, as Lynx_Arc pointed out, LED's are mostly cooled through the back plate. Realistically, I think filling the head with fluid would do nothing but increase the complexity of construction, and ruin any balance, as well as reducing output (even slightly). Time and energy would probably be better spent figuring out how to add more heatsinking (either through increased thermal mass, or increased surface area) to your light.

We had a thread on a similar topic a long while ago, but IIRC, it didn't work out very well: was extremely complicated...

The oil cooling: http://www.ubergizmo.com/15/archives/2005/08/liquid_cooled_c.html

 

[okarina]

Well, yes, the photons hitting your skin, and the glass (or polymer) dome and glass/plastic lens will be in enough quantities that some will be turned into thermal energy. LED's may also emit some slight amount of infra-red wavelength (but probably not much).

The LED generates heat. Heat is thermal radiation and thermal radiation is an electromagnetic radiaton. http://en.wikipedia.org/wiki/Thermal_radiation

Fluids conduct heat better than air, so I really don't know why you doesn't believe in it.

 

[Linger]

many problems with this idea
- yes you feel 'heat' out the front but that's a good thing, for radiated heat out the front has obviously been radiated out the front so those aren't the problem joules of energy that are heating up the back. The issue isn't the joules radiated out the front, its the overwhelming percentage of them that are not radiated out the front that we'll concern ourselves with here.

In short, you don't really seem to understand the problem: passing current through an LED produces heat. The unwanted heat is cleared from the emissive surface via thermal pathway terminating in the metal slug you see at the bottom of all high-powered led packages. Optimizing flashlight performance via improved thermal management concerns enhancements to clearing this heat away from the metal slug at the bottom of the emitter, so your solutions (filling the head with fluid) is really off base.

Fluids conduct heat better than air, so I really don't know why you doesn't believe in it.

(italics are Linger's emphasis)
The main fault in your plan is that you provide nothing for the fluid to conduct heat too.

See problem with any competent design isn't heat INSIDE the flashlight, it is clearing heat outside and away from the light. Getting something inside the light to act as a big heatsink (which is still not what your mis-application would do) is still not solving the problem. Emitter in-efficiency from rising temp is addressed by transfering heat from the outside of the case, either to surrounding air, to the water(for dive lights) or to you hand or mountin system.

>>>Tell you what, you go fill up a big bowl of the stuff and shine a light throught it. Then come back and say if you'd rather the light shine through open air or through the bowl of the stuff.
:RE glass -- have you ever looked through 3" of glass? It isn't pretty. Lots of transmission issues, its just we don't usually notice them b/c we use really small sections. Which is also why leet manufacturores don't use 1" thick lenses and say they are unbreakable - use CPF'ers would get on there and say that transmission losses from that thick a piece are knocking x% off lumens OTF

 

[Linger]

Probably because they read the MSDS sheet.

From the MSDS:

Brilliant application of safety legislation to ward off arm-chair speculation. That was awesome Mnementh, quoting the MSDS...

 

[Mnementh]

Brilliant application of safety legislation to ward off arm-chair speculation. That was awesome Mnementh, quoting the MSDS...

Just advising caution.

 

[John_Galt]

many problems with this idea
- yes you feel 'heat' out the front but that's a good think, for radiated heat out the front has obviously been radiated out the front so it isn't the problem heating up the back.

In short, you don't really seem to understand the problem (heat generated with-in the emitter and transfered out the the bottom slug), so your solutions (filling the head with fluid) is really off base.



See problem isn't heat INSIDE the flashlight, it is clearing heat outside of the light. Getting somethign inside the light to act as a big heatsink (which is still not what your mis-application would do) is still not solving the peoblem, which is actually transfering heat from the outside of the case, either to surrounding air, to the water(for dive lights) or to you hand or mountin system.

>>>Tell you what, you go fill up a big bowl of the stuff and shine a light throught it. Then come back and say if you'd rather the light shine through open air or through the bowl of the stuff.
:RE glass -- have you ever looked through 3" of glass? It isn't pretty. Lots of transmission issues, its just we don't usually notice them b/c we use really small sections. Which is also why leet manufacturores don't use 1" thick lenses and say they are unbreakable - use CPF'ers would get on there and say that transmission losses from that thick a piece are knocking x% off lumens OTF

To okarina

Read this... And go re-read my post. It's not a matter of "believing" in thermal energy, it's that you're trying to address an area that won't yield any good results, will needlessly over complicate a flashlights design over a non-issue, and may not even work to begin with...

By your logic, all the diving lights in the diving-light sub forum should be made so that they flood with water! Think of all the extra cooling the LED's, batteries and electronics will get if they were totally immersed! Heatsinks and housings could be tiny... completely forgetting that electronics will not work very well while immersed in slat water (which will conduct electricity), and Li-ion batteries are likely to explode from the insta-short.

 

[Lynx_Arc]

If you put an LED flashlight close to your face, you can feel that it emits heat, and then you can be sure, it can be heated in the front.

Okay, air transmits light better, it's true. But! The light comes out from the emitter. And it goes through 3 materials. The LED's dome, the air and the front glass. So much of the light is blocked.
When you fill it with a glycerin or cedar oil, it will act like a big glass or a big dome on the LED. These fluid also removes the litle scratches and bumps on the LED's dome.

let me get this straight, if you can feel the heat coming out the light (via light emission) then it is not being trapped in there (by oil) and adding to the heat in the light itself. Think about it.. if you are trying to get rid of heat would you want a liquid filled incan light or not since it also radiates heat out the front?

 

[asfaltpiloot]

There is a catch.
What to do when the oil, glycerin, fluid has heated up.
How to cool it? Can the fluid be kept cool?
Can the flashlight be used when the fluid is hot?

Robert.

 

[Skyeye]

Are the lights on deep diving submersibles filled with fluid?

 

[SFG2Lman]

i think you would also have to leave a fairly large gas bubble in there otherwise once the oil got heated up pretty well it would expand and blow out the o-rings or the lens with no where to go. I personally don't want a light that pees boiling oil on me...perhaps cutting some channels inside the light like in a motor, and filling and sealing those with water, the heat alone should be enough to keep the water moving slightly...probably a nightmare to machine though.

 

[lloydh]

There is a catch.
What to do when the oil, glycerin, fluid has heated up.
How to cool it? Can the fluid be kept cool?

Robert.

Liquids are better conductors than air. In the same way that heat from LEDs currently radiates and (inefficiently) conducts to the head through air, a submerged LED would more efficiently conduct heat to the head where it could dissipate. Regarding why LEDs are currently heats-sinked from behind - well, I think that's blindingly obvious. And the same thermal constraints you allude to apply to metal heat-sinks.

The theory behind the improved heat dissipation is sound. I'm more sceptical about increased light loss, potential for discolouration / contamination, leakages and the boiling point of glycerin (which I'm not too familiar with).

Honestly I think that heat-pipe and active cooling (particularly the former) provide better solutions to current thermal thresholds.

 

[skyfire]

i think you would also have to leave a fairly large gas bubble in there otherwise once the oil got heated up pretty well it would expand and blow out the o-rings or the lens with no where to go. I personally don't want a light that pees boiling oil on me...perhaps cutting some channels inside the light like in a motor, and filling and sealing those with water, the heat alone should be enough to keep the water moving slightly...probably a nightmare to machine though.

theres a certain high powered LED light that uses a non-conductive cooling grease. the design also called for tiny vent holes, and there have been some reports of the grease coming out the vent holes onto the reflector, glass, and LED. just something to consider during your design.

i think you could be on to something, and if you have a good and thorough design idea, you should give it a try!