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 Thu Apr 10, 2008 11:05 pm GMT Reply
Depth makes a big difference as all wavelengths of light start to fall off as the water gets deeper and as they are falling all, there intensity and most imporantly, where photosynthetic corals are concerned, the photo active radiation reduces the deeper the light has to penetrate.
Watts per gallon is an obsolete formula when trying to apply to a coral reef. For example, consider all these light setups have the same Kelvin rating. A 65watt PC fixture will produce considerably less PAR(photo active radiation) than a 54watt T5 HO fixture and a 54w T5 HO with individual reflectors will produce considerably more PAR than the same T5 HO fixture that does not have individual reflectors.
Watt for watt, a single ended or double ended Metal Halide will produce more par than a T5 HO.
4.5 wpg of PC lighting is nothing compared to 4.5wpg of Halide when considering actual intensity and PAR. PAR is what corals that host Zooxanthalae need to live and grow.
PC lighting can be sufficient though, like you say, in a shallow tank or if the higher light demanding coral is kept closer to the top of the tank. You could easily keep mushrooms and Zoa's and some leathers. Some LPS like Torch or frogspawn could survive in that low a light. Just because a coral can survive, though, doesn't mean you could get good growth or even good coloration.
To answer your question simply, wattage per gallon is a useless reference to apply to photosynthetic coral.
Which coral are you interested in?
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