waterproof LED

[hahnmeister]

<a href=showthread.php?s=&postid=10954327#post10954327 target=_blank>Originally posted</a> by daven
But in this case there is a difference. MH is more of a point source and the heat they generate is concentrated in a single place and so it is more likely to transfer the heat to the water. The T5 spread the same amount over a larger area and therefore may be less likely to transfer the heat.

Now if Bean put both in the tank they would both heat the tank equally. Or they would electrocute him.

Just thought I would chime in on this... for the most part Bean is right. But there is a mistake in the above assumption. For conduction and convection, the greater the area means the more heat is transferred. I covered this in another thread a while back where people were debating heat from T5s vs halides (again and again). The fact that halides take up less of the surface area of a tank actually means they have less area to transfer conductive and convective heat across, so the T5s are actually worse in this regard... something I can attest to first hand. The 'thermal pocket' that T5s can create over a tank is much worse than a halide. Now, since if you are at all concerned about the heat in your tank, you are also likely to use fans, this shouldnt be an issue, BUT, radiant heat transfer is another story. The thing is, in most cases, the smaller area that a halide uses above the tank leaves much more open for convective cooling.

With the LED's, yes, LED's arent as efficient as people think. They are just good at focusing that output into a narrow beam for maximum intensity, like a laser. Even the most efficient light sources like a HQI 3000K halide still have about 75% of their electricity converted to heat energy (still waiting on those diode lasers! lol). So those 20w LED's are about the same as an 18watt heater in the tank. The other 2 watts is going to light energy. Now, in a closed system, that would mean its going into the tank... but our tanks are not closed systems (or else we wouldnt be able to see anything inside the tank because no light would escape)... so some of that light stays in the tank, yes, heating it, and some of it escapes... but for all we care, 18w vs. 20 watts is nothing to debate about in the grand scheme of all the energy transfer that is going on in our systems. A 20w heater would put almost all of that 20w into the system as heat. A 20w speaker would not though... unless you were somehow able to capture all the sound and kinetic (from the moving diaphragm) energy it makes inside the system. A 20w motor, if the water it moves is kept within the system, then yes, all of its 20w is really going to heat. Sure, only 10w of it might be actual heat from the pump, but all the work done to the water adds energy to the water (kinetic), and heats the water. This is why some people winter over their ponds by using airstones in the water... the movement of the water heats it and can prevent the pond surface from icing over, even on the coldest of days.'

As I read on though, it seems that others have already covered this information.

 

[G-man17]

Exactly. If you have 20W of LEDs working at 20% efficiency, then you would have a little over 16W of heat transferred into the tank.

LEDs aren't the new big thing because of their efficiency. It's because they can be made to NOT strongly radiate in the IR, they are small and cheap, they are low voltage, and they have a long lifetime. Think about maintenance; you don't necessarily have to change the 1 LED out of 100 to make your lighting fixture work.

Also, when referring to a “small amount of energy leaks out” remember that this is an “eye of the beholder” type argument. 20% can be really high depending on what exactly you are talking about.

Now if you take a 20W laser and put it in your aquarium, you could burn a hole in you fish, make your eyeball explode right before vaporizing a hole in your head, and burn your name into your titanium heater all in a matter of seconds…

 

[G-man17]

On a side note, if your looking for moonlights, the LED can be really low power (relative to a heater) to get the effect you are looking for.

 

[BeanAnimal]

hahn FWIW a loudspeaker is VERY innefficient. A typical loudspeaker is about 1% efficient at turning electrical energy into sound energy. Most of the energy ends up as heat in the voice coil and magnet assembly. If the loudspeaker is in a box (sealed or ported) the compression of the air in the box also accounts for a lot of the energy (this is a complex system.. but very well documented). Sound waves are also very good at exciting the materials around them and turning into heat. So actually a 20W speaker underwater puts almost all of the heat directly into the water. Like the light, some sound will escape, but the energy is rather low.

 

[liveforphysics]

G-man17 - Thank you for your knowledge in this specialized area of studdy. However, I do think you are over estimating the amount of light that would leave the system in this application. If the LED's were pointing straight up and unobstructed, yes a good deal would leave the water. The LED's would also be essentially purposeless in this situation.

My current LED setup uses 40 x 3w CREE XR-E 460nM blue LEDs mounted to the underside of my T5 reflector assembly over my tank. My lighting is mounted to an arm which pivots in the corner to let my lights rotate off the top of the tank.

With the LED's on and the lights rotated to the side, the whole room is bright blue from the roughly 1800lumens of 460nm light. When I swing the lights back over the tank, the tank appears blue, yet the room is a very weak dim blue. I attribute this to a large deal of the light not making it back out of the tank to illuminate the room.

Reguarding lasers in reefkeeping, I sometimes play with my 35mw 405nM nUV solid state laser in my tank. Clownfish see the nUV laser VERY clearly, and nearly all fish are attracted to it. They seem to see the nUV much better than our own eyes. I also have a 250mw DPSS green, and a 200mw 670nM red. The 532nM wavelenth of the green would be pretty useless to the corals. The 670nM red could perhaps be useful to the corals if connected to a simple 2 mirror (galvo) scaning device setup to scan over the entire tank every second or so. It draws around 380mA @ 3.1V, and only makes 200mw of 670nM light, which makes it only about 17% efficient. Are there visible spectrum LD's with 70% efficiency, or only long wavelegnth IR?

To get back to the original intent of the post, useing a few low power LEDs under water will be perfectly fine.

Best Wishes,
-Luke

 

[BeanAnimal]

To the OP

How do you plan to use these things? To add accent lighting and shadows from behind or under rock structures or just as funky disco lights in the tank?

 

[RumLad]

After reading this far, I have totally forgotten what the OP was all about :lol:
Good reading though nonetheless.

 

[95accord]

ok...this is all fine and dandy....but we still havent solved the main issued of getting some waterproof LEDs....lol .... whats a good way to turn regular LED and add a flexible waterproof coating? any aerosol plastic or something that would do the trick?

 

[einsteins]

OReilly outo parts sells an LED kit for attaching to your windshield wipers. They are conpletely water tight.

I have them hanging over my tank for moonlights.

just get an old 12v transormer and wire em up.

I think they were either 15.00 or 19.00

super simple solution to watertight LEDs

Good luck
einsteins

 

[liveforphysics]

I mentioned it above all ready. It worked great. Smear silicone around the connection area of the LEDs. Cheap, flexible, and effective.

 

[xtm]

<a href=showthread.php?s=&postid=10963739#post10963739 target=_blank>Originally posted</a> by 95accord
ok...this is all fine and dandy....but we still havent solved the main issued of getting some waterproof LEDs....lol .... whats a good way to turn regular LED and add a flexible waterproof coating? any aerosol plastic or something that would do the trick?

Solder a clump of LEDs on a PCB and pour fiberglass resin over the module. This is a tight seal.