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Name: Michael
Status: other
Grade: other
Location: FL
Date: May 2007

Question:
We are building a saltwater reef aquarium and have hit problem trying to create the correct lighting fixture. We need to generate 130-150W of light to keep corals. We found 50W halogen lights but have been told that Halogen lights emit white light which has the wrong spectral qualites necessary for corals to photosynthisize. Will placing filters (colored glass) over a Halogen light change the spectral quality of the light or will it merely change the visible color?



Replies:
A colored filter will only remove some parts of the spectrum; it won't add any wavelengths missing from the original light source. So yes, it will change the spectral makeup of the light, but if the corals require some wavelengths missing from that light, a filter won't help.

C. Perkins


Just guessing, don't know about corral in detail, but... Putting a pale bluish or blue-greenish filter that blocks some of the red and much of the IR might do the job. However I think your tungsten-halogens with filter will be less electrically efficient than the right fluorescents or Mercury or Mercury-Halide. You''l be paying twice the electric bill, making twice as much "global warming", and generating twice the waste heat over your tank. Who knows, maybe have twice the probability of starting a fire, because being narrower tubes they run intensely hot. They also don't last nearly as long as the other lamps I mentioned.

Being a technical sticker, I call it tungsten-halogen instead of just "halogen", because it's a tungsten-filament lamp just like other incandescent lamps. A little added Halogen in the tube is just a gimick that allows it to run a little hotter without burning out a lot faster. that makes it somewhat more efficient and somewhat less yellowish, improves the amount of blue for your filters to pass thru to the coral.

Filtered tungsten-halogen will be more nearly a smooth, evenly-filled, natural-sun-like spectrum than the others. But I'm not sure the fish and coral care about color rendition quality as much as people do.

I suspect that cutting off of UV at some short wavelength might also help coral a little, whatever your lamp. To much UV or too short a wavelength is hard on all living organisms.

Jim Swenson


Hi Micheal -

The lighting for your reef tank, as you know, is extremely important for keeping the corals alive. The issue is this - to really answer the question one needs to know what type of corals you have (hard or soft), how deep your tank is, how large your tank is, etc. I would recommend this - go and find a privately owned aquarium store (not a large chain pet store) and talk to the owners or people who work there about the type of tank you have, what corals are in it, etc, and then buy what they suggest. I promise that the lighting will be the most expensive part of the set up - but it's the most critical.

Good luck!



Susannah Sample
University of Wisconsin Vet. Med.



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