waterproof LED

[BeanAnimal]

<a href=showthread.php?s=&postid=10951671#post10951671 target=_blank>Originally posted</a> by easttn
You girls crack me up.

95accord,

There are three basic routes to go for sealing an electronic circuit.

3. Acrylics - readily available, typically not UL approved - but they do have aerosol cans that will protect an LED for our application. Same here with the masking. Last choice imo.

Why not just cast your little project in ACRYLIC resin. You can find the stuff at any crafts store

Now if they guy does not want to DIY his project.. then those lights listed above would work great. Then again one of those LED pool lights you designed would be an eye opener!

 

[BeanAnimal]

I suggest this as required reading for anybody who wants to talk about LEDs in comparrison to other lighting technologies.

http://www1.eere.energy.gov/femp/pdfs/energy06_mccullough_7a.pdf

 

[easttn]

<a href=showthread.php?s=&postid=10951715#post10951715 target=_blank>Originally posted</a> by BeanAnimal
Then again one of those LED pool lights you designed would be an eye opener!

Fair enough. This substrate lived in Saltwater for over a year - tank died first. I reattached the cheesy wires to show operational status. This was an expirment for a customer in the traffic light industry; it out lived my job, the customer, and my tank. :lolspin:

 

[BeanAnimal]

You got your soldering iron out just for me

Now I do feel special!

I wish you would find more time to waste here on RC, it is always fun! You still out of the hobby and living vicariously through us?

 

[Lucky Strike]

beani do agree with you, and not really trying to pour gas on a fire, but everyone thats into t5 always slams MH because of heat, even if there running the same amount of wattage over there tank in t5...

 

[BeanAnimal]

Partly for good reason... partly due to not understanding.

If you look above at the chart above you will see that MH lamps do radiate slightly more energy into the tank, both in the form of useable light and in the form of UV and IR. So in theory they could impart slightly more heat into the water via radiation.

In reality there are very similar. T5s just appear to run cooler becasue the heat is spread out over a larger area. This makes it feel cooler to the touch and also allows convection to remove more heat from the entire unit per volume of air that moves over it. Surface area and convection/conduction go hand in hand.

 

[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.

 

[BeanAnimal]

Umm no... They would be hooked to GFCIs

 

[easttn]

Jeeeeeezzzzzz 10+ hours of bickering- who gives a shi-. The amount of wasted energy spent by an LED in your tank is infinitesimal.

I'll go play in another thread.

 

[liveforphysics]

My very first reef used strings of UV and 460nm blue LEDs solderd to strands of cat5 cable with a smear of silicone over the outside for insulation. I layed them all under the sand pokeing out under the little caves and things. I used a variable current power supply with a little knob I could turn them up and down with. It was kinda neato.


Reguarding the LED's and heating the water thing, Bean is correct here. I am an engineer specializing in fluid dynamics and thermodynamics.

Excluding the light energy which leaves the tank in the form of light, it would act just like a heater of whatever wattage the LED's draw. The amount of energy the leaves in the form of light would be under 5% in the very best case circumstances.

Remember, in something we model as a closed system, energy in always has to equal energy out.

In the case of MH vs T5HO for heating a tank, the quartz plasma chamber of an MH gets warm enough to radiate large amounts of IR at a wavelegnth which water absorbs. The reflector also reflects this IR radiation into the tank water further heating it. A T5HO does not have any part of the bulb become warm enough to radiate IR. This means a T5 must warm the air around the bulb and then transfer that energy into the water from contact between the warm air and the surface of the water. This heat transfer stage involves lots of losses as the warm air often is able to escape rather than transfering that energy into the water. MH is able to directly radiate thermal energy (heat) in the form of IR directly into the water. This is a large part of why people often no longer require chillers when they upgrade from MH to T5HO.

I tried to keep this in as basic of terms as possible, I hope I didn't bore everyone :/

Best Wishes,
-Luke

 

[95accord]

cool.....good info everyone....too bad im not using LEDs to heat my tank....i have a heater for that

 

[goldmaniac]

ok, I will heartily acknowledge that there are others posting on this forum who have more background on this than I do. I'm always willing to listen and learn. So maybe someone can explain the fault in my thinking here:

Bean's Power Conversion Chart, page 1, shows wattage being converted into radiant energy by different 'white' light sources. But it shows that the percentage of energy released into heat varies between 19% and 85-90% by different sources.

Yes, all of the wattages equal 100%. Energy in = energy out. But there are different amounts of the 100% being turned into heat. That's the diffence between the conversion efficiencies of different sources of light, for lack of a better term. Which is what I'm *meagerly trying to* argue in the first place. Am I wrong?

and again, I think the small amount of heat released by LEDs underwater to create moon lights, dim lighting, makes any heat released a non-issue, anyway.

I was, however, very surprised to see how less efficient LEDs are than I thought. good to know.

Can someone explain the fault in my logic? that 20w delivered to a device does not necessarily ALWAYS result in 20w of pure heat? I am considering light released as NOT a source of heat, or at least not 100%?

Am I wrong in the assumption that light released is not simply an intermediate step between power source and heat dissapation? (sp?) These are not incandescent heat lamps, after all.

I am genuinely interested in finding the flaw in my logic.


G.

 

[BeanAnimal]

The chart shows what form the energy takes after being used (transformed) by the device.

Notice that the LEDs actually produce more RAW heat than MH or FL (in the form of conduction and convection). The heat is carried away via the LED die and/or attached heatsink.

Notice the the Incandescent bulb produces more RADIANT heat than any of the others.

Anyway back to your basic question. Energy is Heat. When that light is absorbed by the mass around it, it turns to heat. Now some of it may cause a chemical reaction (photsynthesis) that in turn adds biomass to the tank. But rest assured when that biomass dies, it will release the heat Again this is a very small percentage anway and not really worth talking about esp in the context of a few watts of LED light.

So you need to rethink your understanding of "pure heat". Stand in front of a sun filled window and feel the warmth on your skin. The light is striking your skin and being transformed into heat.

Yes, your are correct a few LEDS in your fish tank are not going to be a problem. The point was that if you put 20W worht of LEDs into the tank, you should expect somewhere close to 20W worth of heating. As shown by the table above 85%-90% of the energy consumed by the LED is transformed directly to (to use your terminology) PURE HEAT and will be siphoned off by convection and conduction into the tank. That leaves 10%-15% that is leftover for light. Out of that 10%-15% only a fraction of the energy will leave the tank or be used for photsynthesis, the rest will be absorbed as heat by the mass of the tank.

 

[goldmaniac]

ok, I think I see the difference in thinking...

I was incorrectly considering the conversion to light as the final stage of energy, where you're saying that even though some energy is turned to light, that light is only an intermediate step before eventually producing heat. I don't want to misquote, this is what you're saying? In that aspect, you're right; I'm wrong.

Additionally, take this aspect, and combine the LEDs (in)efficiency of 85-90% heat production during power conversion into light, and you're right again. 20W going into LED's will produce 85-90% of 20W worth of heat, and that's not even considering the radiant heat produced by the light of the LEDs themselves. That difference is too small to argue.

Thanks for not being a jerk during this argument. friendly arguments get too ugly on RC too often.

 

[BeanAnimal]

All forms of energy are at an intermediate step before being converted to heat

As you can see one of the nice things about LEDs used in fixtures (like the SOLARIS) is that less heat is RADIATED from them. So if you can remove the conducted and convected heat before it is transfered to the water, then you get very little heat transfer to the water "cold light" per say. The UV and IR are not there to radiate into the tank. However, where most peoples understanding breaks down is that the 400W MH and 400W LED system both put the same NET amount of heat into the room.

We put LowE coatings on our house windows to block the UV and keep the sun from heating our homes while still providing light. The LowE coating reflects the UV away from the glass on the outside but also reflects UV and IR on the inside to keep a warm house warm in the winter.

Learn a little about energy and it explains a lot of the world around you.

 

[kgolem]

I too was thinking along the same lines as goldmaniac. After a bit of research and further reading of this thread I see what you are saying and follow your thought process BeanAnimal.

It would be interesting to have a container that could entrap all forms of energy and not allow anything to escape. I was thinking that the light from the lamps would not be counted, likewise the kinetic energy from rotating motor shaft. My mental model had the shaft connected through the box to an external mechanical load. I also pictured sound escaping from the box by transference of pressure waves through the box walls by flexing the box structure.

This is why I didn't agree with your statements. I was considering a more practical as opposed to theoretical situation.

This, from Wikipedia... I like the conciseness of this paragraph.

As the universe evolves in time, more and more of its energy becomes trapped in irreversible states (i.e., as heat or other kinds of increases in disorder). This has been referred to as the inevitable thermodynamic heat death of the universe. In this heat death the energy of the universe does not change, but the fraction of energy which is available to do work, or be transformed to other usable forms of energy, grows less and less.

Peace?

 

[G-man17]

Although I don’t post much (since others are usually experts on a topic that I am not), I am finishing my PhD focusing on semiconductor quantum optoelectronics (read as I make lasers and LEDs) and feel obliged to chime in. I do not google search my comments. These are all from training, experience, and research.

Some commercial LED manufacturers are now boasting >20% efficiency in their visible spectrum LEDs. Which still means that around 80% of the power used will be converted to heat. Putting the LED in water should slightly increase the overall "optical extraction" efficiency due the LED being able to radiate more light externally compared to when it is in air. Even so, most of the power still goes to producing heat. I agree with Bean on this part (as I do with almost all of his technical teachings).

However, it is incorrect to say that only a small fraction of the light will leave the tank. Seawater is not that absorptive in the lower part of the visible spectrum (<0.1/m from a paper in the journal “Applied optics" vol 20 pp 177. use e^(-0.1*length in meters) to get % absorbed). Most of the generated light will not be absorbed and turned into heat; it will come out of the tank. Think about the fact that you are seeing the LED. If most of the light is absorbed you wouldn't see it. To say that all radiated EM energy is turned into heat it not necessarily true. For it to result in heat, it has to be absorbed or excite vibrations in the atoms through which it passes. IR radiation (like what the sun produces) excites a lot of vibrations, which is why we think of it as radiant heat. Visible light (particularly below the red wavelengths) in saltwater doesn't do so much. To EM radiation, your aquarium is very far from being a closed system.

Now if you want to be dangerous and light up your tank with diode lasers, you can get >70% efficiency.

sorry for the rant
-Tony

 

[BeanAnimal]

G-man thanks for your post.

I should have qualified a "small fraction" by stating that the escaping energy is a small fraction of what is pumped in. I would agree that a significant portion of emitted light does find its way out of the tank at some wavelengths. My point was that those same wavelengths that make it out of the tank do not account for much energy.

I would also agree that an aquarium is certainly not a closed system. For the sake of our conversation it is close enough for the bulk of the energy (at least in my opinion). I would argue the same holds true for the room that the equipment is in.

 

[cannarella]

<a href=showthread.php?s=&postid=10957649#post10957649 target=_blank>Originally posted</a> by G-man17

Now if you want to be dangerous and light up your tank with diode lasers, you can get >70% efficiency.

sorry for the rant
-Tony

Would that be "Sharks with Freakin' lasers on their heads?"

Sorry couldn't resist.

 

[goldmaniac]

if we're going to go back to Theory as opposed to LEDs and aquariums, then the escaping light from LEDs illustrates my point that not all Wattage is converted into heat in the aquarium. Some energy leaves the aquarium, and the equation.

But my newly-learned inefficiency of LEDs prohibit any sane argument. The vast majority of wattage goes into heat loss in the first place, and only a small % of the energy is converted to light, anyway.

Any light escaping the tank keeps the energy in = energy out equation from balancing. But it's insignificant. If I wanted to be a jerk I'd keep arguing this point, but that's not productive.

But I don't think you can argue for both Theory and Real World situations at the same time, here. they vary and I think that's where this discussion becomes pointless.