Thursday, October 15, 2009
LED Planted Aquarium Lighting: Part 2
In the first part of the series on LED lighting in the planted aquarium, I discussed whether or not LED lighting would work for growing live freshwater plants, and if so, why hasn't anyone made a fixture you can buy yet that isn't $1,000+. Now if you're either brave and the DIY type or have some deep pockets and want to give LED lighting a try, but need that extra justification to give you a push, here are some quick pros and cons of LED lighting in the planted aquarium:
First, the pros, and there are lots of them. You'll find that most come with some caveats though.
The first one that jumps into many people's minds is their lower energy consumption. Most high powered LEDs (the sort you use for growing plants) only use 2-4 watts of electricity and pump out anywhere from 100 to 300 lumens (for comparison a 70 Watt metal halide bulb produces around 5000-6000 lumens). So depending on the size of the aquarium and the quality of LEDs that you buy, you could see a slight drop in power consumption. However, this drop is not huge, contrary to popular belief. If power saving is your main qualification, I'd lean more towards T5 fluorescents (these usually put out about 2000 lumens for a 24 watt bulb).
Another benefit of using LEDs is that they don't emit quite as much heat as high temperature metal halide lamps do. Again, there have been misconceptions about LEDs thinking that they don't create much heat at all. Regular low powered LED's don't really, but high output LEDs do. Substantial heat. So much that you need heat sinks and fans to keep them cool. Granted, they don't get quite as hot as metal halide lamps, but they require more robust cooling systems than any fluorescent fixtures. And heat is critical determinant to how long an LED lasts, which brings me to my next point.
LEDs last a long, long time if they are treated right. This is a huge benefit over fluorescent bulbs that dim or shift their spectrum and need to be replaced every 8-12 months. I just shelled out $70 for two new bulbs for my 2 x 96 Watt CF fixture and will need to do so every year. LEDs should last the life of your aquarium (or at least 50,000-100,00 hours) provided their temperatures are controlled. You see, the lifespan of an LED is directly linked to its operating temperature. The hotter they run, the sooner they burn out. This is why heat sinks and cooling fans are necessary.
Another big difference between bulb type lighting (fluorescent and metal halide) and LEDs is that LEDs do not require fancy reflectors. They emit all of their light in one direction via highly efficient internal reflectors, and therefore eliminate inefficiency due to light bouncing off the reflector and back into the bulb or off into the room instead of into the tank. If you are putting together your own DIY fixture, this means that buying a reflector isn't always necessary (depending on your LEDs) and can save on costs and space a bit.
LEDs are small, and produce a lot of light in a very small space. Only metal halides pack as much light in a small space. Try lighting a nano tank to levels that qualify as high light with a flourescent and you'll see why this is awesome. In order to be high output, fluorescent bulbs need length...and that won't work on a tiny tank (except spiral CF bulbs). You can't really put a 70W metal halide over a nano tank either, unless you're planning on boiling some water. This small space footprint also brings up another benefit of LEDs, although it is purely aesthetic.
LEDs produce that ever-illusive shimmer effect. You know, the glimmer in the water that sun casts that just looks so awesome. Until LEDs, only metal halides could do that, since they were the only other point-source (meaning all light is emitted from a small area) fixtures available to planted aquarium keepers. As stated before, metal halides don't really work over smaller tanks for obvious reasons. Now those of you with smaller tanks can bask in the shimmering glory as well!
Finally, LEDs can produce exactly the wavelength of light needed by plants. There are very specific wavelenghts that plants use for photosynthesis, and if you didn't care much about how the planted tank looked to the human eye, you could buy LEDs that only emitted these wavelenghts. Of course, that wouldn't look very pretty...or natural, since it would be only red and blue light. But the point is you can control the wavelengths present in your lighting, instead of a wide range produced by other types of lights.
There are a few cons to LED fixtures, the largest being cost. LEDs are just too expensive still to use for large aquariums and provide the light necessary for plant growth. At approximately $10 an LED, not including controllers and cooling systems, the costs quickly add up. It's easy to see how commercially produced fixtures like this one sell for $700-$1000. Eventually, the costs will come down as high output LEDs are put into more and more applications, but for now, we're stuck with paying for this new technology.
Another downside of LEDs is that they still produce a large amount of heat. They aren't the ideal solution for aquariums that are highly sensitive to heat, or in hot climates where keeping the tank cool can mean running a chiller or blasting the air conditioning. They don't quite reach the temperatures of metal halides though.
And finally, considering there are only a few large commercially produced LED fixtures available, if you want to light a smaller tank, or if you can't afford the large fixtures, you'll probably have to make your own using parts bought online. This requires soldering, wiring, and constructing a housing that can effectively cool the LEDs. It's no small undertaking, but it is possible and fairly straightforward.
Final verdict: If you have a small tank (too small for most fluorescent tubes and metal halides), some electrical DIY experience, and don't mind putting together a cooling system, a small LED fixture is probably your best option for high output lighting.
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