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Suggested Reading on Lighting and Photosynthesis:
(1) Photosynthesis 4th Edition, D.O. Hall and K.K. Rao, New Studies in Biology, Institute of Biology, London, 1987.
(2) Light and Photosynthesis in Aquatic Systems, John T.O. Kirk, Cambridge University Press, 1983.
(3) The Biology of Marine Plants, M.J. Dring, Contemporary Biology, Edward Arnold, 1983.
(4) Primary Productivity in Aquatic Environments, Charles R. Goldman, University of California Press, 1974.
As well as many other books dealing with photosynthesis in macro and other type of algae.
12.2 REQUIREMENTS:
Premise 1: To provide lighting that is beneficial to all lifeforms kept in an aquarium, not just a few, we must provide more than a narrow spectral band of light, or light skewed towards a particular part of the spectrum.
Using specialty lighting does not meet the above premise and is, as a result, not recommended. It is not the best type of light that the hobbyist can use over his, or her, tank. It may not do any harm as such, but the hobbyist can do better. As an analogy, it is a bit similar to taking only one type of vitamin when, in fact, you should be taking a multivitamin supplement.
Premise 2: If, as we have seen in the introduction, intensity is important because of the modern interpretation of light energy that quantity can be more important in photosynthesis than the type of light offered, lighting that can provide very high intensities seems very desirable, and fits the requirement.
Specialty lighting, which includes actinic lighting, does not usually offer strong intensities and does not fit this premise either. Certain types of other lighting offered, e.g. regular fluorescent tubes does not fit the picture either, unless many bulbs are used. Because several types of fluorescent tubes can be obtained in an H.O. variety (high output), such bulbs can be used, as long as enough of them are placed over the tank, as in such a case they will fulfill premise 1. Newer aquarium light fixtures can now house multiple bulbs, are to be preferred.
Premise 3: If we are believers that, whatever works over a natural reef is what we should use over our own tanks, then certainly, day light type spectra should be strongly favored, as such is the spectrum of sunlight.
The daylight spectrum is defined as a 5500 Kelvin degree spectrum. Many fluorescent tubes with daylight ratings exist, for example Vita Lites, Spectra-Lites and so on. Such bulbs are excellent for use over the reef tank.
Conclusion: Putting the three premises that I have suggested together, it becomes clear that what we need is a very high intensity of light, with a 5500 K rating. If a bulb meets these criteria it will include the blue and actinic spectrum as well, because day light does.
Such bulbs exist. They are of the metal halide type. They are the bulbs that I have been advocating for a long time. They are now finally available in North America from a U.S. manufacturer: Coralife. I suggest you seriously consider using them. Certain Osram Power Stars also fit the picture, but are presently not available in North America in the 5500 K rating.
Alternatively, use fluorescent tubes with a 5500 K rating, and use as many of them as you can, as the intensity premise needs to be fulfilled as well. This sometimes poses problems because of the limited amount of space available above a tank.
Using high output (H.O.) bulbs is certainly better because you will typically gain 25% to sometimes 50% more light. Unfortunately the V.H.O. bulbs (very high output) change their spectrum too rapidly, although they can be used for yet an additional gain in intensity. You must, however, replace them frequently to compensate for the spectrum loss. Usually every 4 to 5 months.
Two options are available as you can see. Pick the one that suits both your situation and your budget.
12.3 REMARKS ON INSTALLING LIGHTING:
Not all lifeforms kept in a reef tank need the light intensities that were discussed so far in this chapter. Some may need only moderate amounts, and others may be night type corals, requiring even less.
You must try to identify which ones you have placed in your tank. One easy way to do so is to look at your tank after the lights have been out for some time. Any coral that opens more, or wider, while the lights are out obviously does not require very strong lighting and should be placed in a protected area of the tank. Ledges can be built using pieces of rock, or coral, to accommodate such lifeforms. Leaving them in strong metal halide or fluorescent lighting will quickly damage them. As a result your tank must have a high and a moderate to low lighting zone.
To prevent strong lights from heating the aquarium water, you must ensure that hoods are equipped with fans, and that pendant lights are hung about 12 to 15 inches from the water level. Make sure too that all lighting equipment is firmly in place so it cannot fall in the water. Protect yourself, it happens, believe me, especially with children around the house.
Certain types of metal halides, e.g. halogen quartz iodine lights, may need to be protected by a U.V. filtering glass. If you do not place such a barrier between the light and the tank corals may be burned by the ultraviolet radiation. Osram Power Stars need such shields. Coralife's and Venture lighting bulbs do not.
You may have read in certain articles that metal halide lighting "burns" corals. This can only happen if you are using a bulb that needs a U.V. shield, and omit to install it. Other bulbs may result in some corals taking on a brownish color. This is not coral burn! It is a normal occurrence: symbiotic algae are growing inside your coral and giving it a browner color than it used to have.
Changing over from regular fluorescent lighting to the much stronger metal halide type should be done in steps. Do not switch from a low wattage setup to a very strong one overnight. Acclimate the tank to more and more light progressively. Do so by restricting the number of hours the lights are on, and/or the amount of bulbs that are on at one time. Take several days to a week to complete the change over. As with all changes made to the reef tank, you must go slowly.
How many hours should your lights be on? I recommend a total of 12-14 hours, depending on how much intensity you are providing. If yours is a tank with about 3 watts per gallon, leave the lights on a little longer, perhaps as much as 14 hours. If however you provide close to 5 watts per gallon, 12 hours will do.
Try to stagger the on and off of the lights, especially if you are using three or four of them. In a four light set up with the lights called A, B, C, D, the pattern would be as follows, (this is an example and you can substitute your own times):
Of course, many variations exist, especially if you are using a different number of bulbs. Work out your own lighting schedule based on the number of bulbs and intensity used.
12.4 CONCLUSION:
The last word on lighting has not been said. As time goes on more evidence pointing in the direction of 5500 K metal halides will become available, and make those skeptics out here believers, the way I am, and have been, after many years of using such lights, first European imports and then the U.S. Coralife ones. These bulbs are now available in 175 watt strength from many dealers.
Perhaps stronger versions of 5500 K fluorescent tubes will become available too, making the lighting set up for the reef tank not quite as pricey, and easier to manage for a lot of hobbyists. Metal halide lighting is not inexpensive, but as far as what is now available, it is the best.
I welcome calls from any hobbyist who wishes to discuss lighting more in detail, or ask questions about specific situations, and can be reached at Aardvark Press.
Lighting is, indeed, one of the more complicated areas that the hobbyist has to deal with, and is often misunderstood. Moreover, advertising is often skewed to make one particular feature very attractive, confusing the hobbyist even more.
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