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Tony: An LED question.

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sfsuphysics

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So I asked the other day, somewhere else, why they don't incorporate fans into LED fixtures since they're really touchy if it gets to hot. Now I understand the argument of if the fan dies you don't want the LEDs to go belly up so you want it to be able to passively cool itself. But to me sounds like you can do that, AND add fans simply to kick it up a notch reducing temperatures even further.

Well one response I got was this...

"The reason LEDs are designed into fixtures that don't require fans is that LEDs are solid state technology and therefore they are designed to operate with passive heat dissipation instead of fans. Designing LEDs into packages which require fans would defeat and undermine the whole purpose of solid state technology."

Now to me it seems a bit like hogwash, or just poorly misworded, the whole "undermine the purpose of solid state technology"?? I thought the purpose of the LEDs was to have high output light at low wattage, period. Now it took a lot for me to to argue back, because for once I might be wrong :D So Tony, what say you o' expert of the diode that is lit!
 
that's interesting! solid state technology is such a bad buzzword, it describes nothing.

I see a lot of LED light bulb replacements with big heatsinks on them, but no fans. On aquarium LED fixtures, I see fans. It'd be great if LED solutions required no fans so that there would be no extra noise.
 
The solaris and aqua illuminations fixtures both have active cooling built in. The elos doesn't. Familiar with other systems.
heat kills LEDs. without active cooling (required in almost all applications we are interested in), high power LEDs can function, but they will exceed their "max" junction temperature drastically lowering their life.

"is that LEDs are solid state technology and therefore they are designed to operate with passive heat dissipation instead of fans."
is absolute ad utter bullshit. Technically speaking, passive or active isn't the issue. Staying below threshold is the issue. You won't operate high power LEDs below threshold in the density we use without active cooling .

There are SOME cases where active cooling in our applications isn't necessary, that that may be for an adequately heatsinked moonlight/accent light. This is because either the density of LEDs are low and/or they aren't driven as main lights (ie,not at 700-1000mA)

here are a couple of useful links (including chars/studies on heatsinking options) on thermal management from the people who actually make the emitters
www.cree.com/Products/pdf/XLampThermalManagement.pdf
www.philipslumileds.com/pdfs/AB05.pdf
 
couple things to keep in mind when thinking of passive cooling:

Convection IS your "active" fan. If you don't have GOOD confectiveflow, then surface area doesn't help you much

A large heatsink without heat transport out, more or less just takes longer to get really hot compared to a smaller thermal mass.

It is much easier to passively cool a high power LED running at 350ma than at 1000mA
 
Thanks Tony, pretty much what I was thinking, however I didn't want to go on tirade and point out "umm you're wrong" too many times :D

Another was an article in the latest Advance Aquarist where the article writer stated the reason for tides is because the Moon has a stronger gravitational pull than the Sun... now that one I had to comment on :D
 
http://www.advancedaquarist.com/2009/9/short

Article is actually about dry exposure of corals (i.e. carrying them in your pocket on planes as opposed to inside of a bag of water)
 
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