Flashlight's head filled with fluid!

[csa]

You might actually improve light output slightly by lowering the difference in refractive index between the surfaces of the light. Since you have several surfaces (the inside of the lens, the dome of the LED, the reflector itself), you could see a very minor benefit which might (at worst) offset the loss of light in the liquid.

 

[petersmith6]

liquids will expand when heated so will force its way out

 

[Unicorn]

It might work for a little while on some super hot wire mod, but unless you have some sort of cooling device for the oil, it won't last for long. The oil itself will heat up and that heat will have nowhere to go. The same problem has happened with some people who tried out using mineral oil for cooling PCs. The oil would take hours to heat up, and did a tremendous job of keeping the CPU, GPU, RAM, etc cool for that time, but eventually it did heat up. To make it worthwhile having some sort of radiator would still be needed.

 

[Roger999]

liquids will expand when heated so will force its way out

This. No one wants a sign on the bezel saying "lens may explode when over heated".

 

[McAllan]

This. No one wants a sign on the bezel saying "lens may explode when over heated".

Well, since there's no air that will not be the case. Yes it can crack the lens but it will not explode as the fluid cannot compress. The pressure is released as soon as the glass crack and there is no further pressure to get the glass flying.

It's an interesting idea. Don't know how practical however. A bubble design is not optimal but a design with an expansion chamber like on heater systems might work great. Made out of the same metal as the vacuum can (aneroid cell) in aneroid barometers as it's has been proven very resistant to resist metal weakening for decades or even centuries. And it doesn't "rot" like rubber would. That way you could full fill the need for expansion of the fluid as it heats up while avoiding the need to have a bubble.

 

[McAllan]

It might work for a little while on some super hot wire mod

Wouldn't you want the surface of a halogen bulb to get hot?
After all that's the whole principle in a halogen bulb. Otherwise it'll get black very quick.
The principle is that the metal that evaporates from the hot wire cannot composite on the glass but re-composites on the hot wire.

See the halogen cycle on Osram/Sylvanias homepage.

 

[gcbryan]

I'll just throw out what I know.

Glycerin has a higher boiling temp than water (I know that from a past company I worked for where the assembly people tested a switch meant for truck engines and needed a higher temp than they could get by boiling water).

People have put mineral oil in flashlights to make them dive worthy. You don't have to worry about water coming in if you fill the entire flashlight (including battery compartment) with oil.

It's the salt in salt water that causes the circuits to short out.

I think it's got to degrade the light output going through oil rather than air however. It's messy. Especially in the way it was done with dive lights since the battery compartment was filled as well. It's messy changing batteries. If it leaks that's messy as well.

It is a quick and easy way to turn any flashlight into a dive light.

In the particular application we're talking about in this thread it doesn't seem like the best solution to the problem.

Certainly just filling the head doesn't do much. If you fill the entire body as mentioned it would work for a while but so would a proper heat sink and a tight fit to the aluminum body to conduct heat from the inside of the body to the outside of the body and then away from the light.

If we're talking about really powerful emitters I think it would be easier to put vent holes in the body, forget about it being water resistant and install a micro cooling fan in addition to a proper heat sink design.

 

[Johan13]

You might actually improve light output slightly by lowering the difference in refractive index between the surfaces of the light. Since you have several surfaces (the inside of the lens, the dome of the LED, the reflector itself), you could see a very minor benefit which might (at worst) offset the loss of light in the liquid.

The refrative index doesnt actually lower the output. The speed of light will be slower in substances of higher RI. For example, the glass will slow down light slightly, but it will pick up speed once it reaches air again.

The liquid, unless completely pure can act to reflect light. This would hurt your output. Having a bunch of liquid, would be like having a really fat glass lens which isnt very good. This is one of the reasons why telescopes use mirrors rather than glass lenses. For a large lens, it must be very thick at the middle to focus the light. It is very hard to have glass perfectly pure when it gets thicker.

Just a little bit of physics ive learned this term :)

 

[Mr Bigglow]

Magnetic compasses of any sort of quality are usually oil filled and I've had a fair bit of trouble with them leaking after being dropped etc. Changes in air pressure also will have to be considered, esp when flying. A common compass thing is an air (or is it a vacuum?) bubble forming inside the oilfilled compartment when the outside pressure drops, even with normal weather changes- would not want that drifting around in my light. I do commend the noble effort. Give it a try!