12.1 INTRODUCTION:

Lighting already was a most controversial subject when the first printing of this book hit the stores in early 1988. It still is, perhaps even more so, now that the seventh printing of this book is out. Whereas a few years ago the controversy was over whether to use metal halides, or metal halides combined with actinic lighting, it has now expanded to include many other forms of lighting offered for sale in hobby magazines such as, for instance, a number of specialized type fluorescent tubes that have been introduced in the early 1990's.

While I am certainly not saying that you cannot run a reef tank with fluorescent light, as long as you use the right ones and enough of them, in my opinion, everything that surrounds lighting the reef tank, is a matter of degree, more than a matter of controversy. It is similar to the performance of cars. Porsche and racing cars do a hell of better job at it than others. Does that mean the others won't get you to point B? Similarly, at least two types of lighting can do the job for you, as we shall see later, but each provide a different degree of efficiency and ease of use.

Heated arguments can be read in magazines as to what lighting is best, and why you should use only bulbs from such and such a company. What it really all comes down to, though, is "do the corals in our tanks look healthy and large, and are they surviving for long periods of time, more than the usual 6 to 8 months that most hobbyists experience with the lights used?

Articles authored by other hobbyists gain fame because of some new twist they introduce, or some "experiment" they conducted that no one can verify. All very confusing to me, and to many hobbyists I am sure. Who are these "experts" anyway? How much do they know about lighting and photosynthesis? Or are they just looking at brightness, or appealing colors, or how one or two species of corals react?

Sprung (1989), a marine biologist, makes a case "for" actinic lighting and a case "against" metal halides, but offers very little substantiation for his strong position. He has done so for about two years, when his name first appeared in magazines, working for a company that was heavily into selling actinic lighting. To be fair, his strong stand "against" was recently mollified (Sprung, 1990) and he now offers a more moderate approach stating that "certain" types of metal halides must be avoided. Such is, however, again skirting the issue; which metal halides and especially why? Again, no information that can be easily related to. Or not technical information that one can verify in other books. Mind you, I respect Mr. Sprung's knowledge a lot and think he has done a great deal for the hobby, but in the lighting area he has not convinced me.

The only light that shines over natural reefs day in and day out, for months on end, and year after year, is the sun. The strongest light available in nature becomes corals fine, and allows them to build reefs and multiply unhindered. Granted, it is attenuated by clouds, refraction, water depth, turbidity, and so on, but it is still stronger, when measured with light measuring equipment, than whatever the hobbyist can possibly place over his aquarium, save perhaps Xenon arc light. And strength of light is important under the new photobiologic approach, as we shall see later.

Note: The explanation in this introduction may seem too technical to some, for which I apologize if you have no interest in how one arrives at the conclusion that I have arrived at myself, namely that metal halides are high on the list of lighting types to consider for your tank. It is the only way for me to try to convince the reader that there is merit to the claims I make. Without explaining, my position would do the reader a disservice, and would not give him, or her, a chance to evaluate what I stand for, and verify some statements in other literature.

The sun over the reef can at times develop 150,000 lux at sea level. Strength or intensity of light is important, but not the only factor that needs to be considered. Indeed, which type of light the corals receive from the sun, and which type they can absorb is an important factor too.

Because water filters out certain portions of the light spectrum, and because blue wavelength lighting passes through the water to greater depths, some have suggested that such blue light should be maximized for the corals to thrive, to the detriment of all other lighting they require, and to the detriment of what other corals may need.

Nothing is, in my own experience further from the truth. Providing too much actinic wavelength is harmful at best. Short wave light, defined as a narrow spectrum around 300 to 320 nanometers by those strongly advocating actinic light, is only a small part of the light energy that corals, and other animals in the tank, require and can utilize during photosynthesis. Providing a more complete spectrum by using a different light source, has always given me better results, and has allowed photosynthesis on a larger scale.

Phillips, whose bulbs were touted by many an entrepreneurial so-called expert, were the first surprised to find out that such bulbs were used over aquariums. Granted, their nanometer range is important for photosynthesis' photosystem I, but so are the higher 670-680 nanometer ranges for photosystem II (see later and see references). Photosynthesis is an extremely complicated matter, especially in aquatic environments. Those wishing to read more on the subject are referred to a textbook on the subject by Kirk (2), or one of the many textbooks on algae, especially the sections dealing with photosynthesis.

There is no question that blue wavelength lighting has to be provided, but this can be done as part of a much more complete spectrum, for instance the one provided by metal halide lighting of the 5500 K type, but I am jumping ahead of myself.

In photobiology light energy is nowadays measured quite differently than it used to be. Rather than using lux, or foot candles, or lumens, the preferred unit of measurement is now the photon, or photon irradiance, a unit of measurement derived from Einstein's law of photochemical equivalence(2). These units are used to determine how much energy a molecule can absorb from a certain type of light.

Einsteins are defined as the amount of energy absorbed by one mole of a compound (mole = gram/molecule). Since different types of light have different wavelengths, and since each wavelength provides a certain amount of "energy", calculations can be made of how much "energy" can be derived from whatever amount of a particular wavelength that, for instance, algae, more specifically symbiotic algae absorb. More irradiance from a low energy type of light would give a higher total energy level than less of a stronger energy type of light.

It is, moreover, a fact that photobiologists have greatly advanced their knowledge of photosynthetic processes that take place in aquatic environments, and that one of the great changes that has occurred is the stronger belief that photosynthetic processes depend more on the number of photons of irradiance that reach a surface than the energy content of these photons(1).

If such is indeed correct, which, not being a photobiologist I have no reason to doubt, then, providing more intensity of each spectrum type (blue but also many others) will achieve a far higher energy absorption level than just providing strong light skewed towards one particular spectrum (actinic). Higher energy absorption means higher levels of photosynthesis, means higher rates of metabolism and reproduction, which is to the benefit of corals and invertebrates that harbor symbiotic algae.

Likewise, because photosynthesis does not take place in just one specific area of the spectrum, but over a much wider range(1), providing high intensities of light of various spectral lengths benefits the process and benefits the corals and invertebrates that harbor symbiotic algae, because photosynthesis is what makes them, and the corals they live in, thrive.

Photosynthetic algae contain pigments that assist in the uptake of light energy, these pigments start and sustain the photosynthetic process. We should be strongly interested in promoting this process because the corals and invertebrates kept in our tanks feed off the by-products of this process. This is, for example, the reason why many can survive without external food sources for extended periods of times.

The nanometer levels (wavelengths) at which this occurs vary, meaning the types of light at which this process occurs vary as well. Below are merely a few examples of nanometer ranges and the pigments involved (adapted from (1):