L.E.D. vs HALIDE/T5/VHO

[OceanicCorals-Eugene-]

Originally Posted by sphelps

Proper design of a heat sink could maximize the inductive heat transfer eliminating the need for fans. Fans are needed in the current fixtures because the heat sinks are simply standard units not designed specifically for LEDs and therefore requiring addition convective cooling. Designing the heat sink to concentrate additional surface area at the LED locations would be the first step. There are also different grades of aluminum or other materials which offer higher inductive properties than what is probably being used. Fans simply cut the cost of the heat sink dramatically which is why they are used. Eliminating the fans would actually increase quality and reliability since fans often fail or become restricted over time which could result on over heating. Also using fans will result in an uneven heat distribution meaning some LEDs will run warmer than others. These two problems could explain why fixtures have suffered from LED failure, I can't imagine any fan lasting for 10 years over a SW aquarium. Eliminating the need for fans would definitely increase reliability.

If you look closely at well designed heatsinks they all incorporate fans to dissipate the heat and thats because most components work better at lower temperatures. One of the things that you see heatsinks on mostly are computer parts, there are heatsinks that are "silent" and require no fan but run the processor at 10-20C higher than the same heatsink with fans. The design of the heatsink itself is definitely going to help with the heat dispersion but if these units are run without a fan you/we can all expect them to never meet the 50,000hr that the manufactures claim. The main reason is heat, the lower the heat you can keep on the LEDs the more efficient they run, and the slower the intensity drop on the LEDs as well. If you want to see an example, wire some 5mm leds and put them in isolated environments of room temp, 50C, 80C you will no doubt see the 80C intensity drop along with a major color shift as well.

If manufactures actually source out reliable fans for there fixtures, like those found into computer cases, low RPM high CFM fans the units will be near silent yet still provide the cooling needed for the LEDs. Some companies will still try to build fanless LED fixtures, elos is one that comes to mind, but they dont drive the LEDs to its full capacity in those fixtures. But again it all comes down to what the company wants to do with the units, so i think what needs to be understood is how to channel the air flow inside the fixture itself to provide efficient cooling so that all emitters get cooling thats somewhat the same.

[Ron99]

I think it is not only heatsink design but the overall fixture design as well. Convection cooling can work if the heatsink is open to the air and visible. if you want to enclose it in a housing then you need fans to help move air. And even if open to the air fans will help keep the LEDs cooler than convection cooling alone.

My fixture is enclosed in a housing and I am running 3 low RPM computer fans. I cannot hear the fans at all (well maybe if I put my ear right next to them) and my heatsink is very cool. So I expect very long life out of my array with no noise. The fans should last as they are low rpm thus putting low stress on the bearings and are on top of a closed housing. Unless the location of your aquarium is excessively humid or you frequently splash water up and over your light fixtures I don't see fan reliability being a huge problem.

If you look at the Solaris fixtures that suffered LED failures it was not likely due to the fans but to the fact that there were no real heatsinks to help draw heat away. The heatsink setup of the Solaris units was completely inadequate and I do not think it is representative of what should and could be done with LEDs.