For as long as I have been in the hobby, and that is quite a few years as most of you know, lighting has been a hotly debated topic, both in the saltwater and freshwater side of the hobby. It is is my opinion that this will continue for years and years. The main reason for this is that there really is no way to arrive at a concensus of opinion because of the many variables aquariums exhibit and the fact that each aquarium is different from the Next one.
Let me preface this "chat" by stating that I, too, do not have all the answers by any means. In fact, I don't think anyone does because of all the variables we need to deal with when it comes to aquarium lighting.
What I am going to do is put forth a few ideas and topics that we can discuss and elaborate on when we get into the question and answer part of the "Chat". Some may sound controversial, or unusual, or not what you are accustomed to read or hear and that is OK with me. That will give us more to chat about as I am allowed to clarify what I really mean after these introductory notes are transmitted. Others are basics, dealing with lighting and energy. Mind you, the basics are not that basic. They are pretty hard to understand and that is why I have not gone into great detail on them but if you wish more info, you are welcome to email me.
So here we go :
1. Lighting requirements are dependent on the animals, not on the size of the tank. These animal specific requirements apply to intensity, to Kelvin degrees and to the type of bulb(s) used to produce the desired strength (corals perceive light as energy, and that energy is what really counts).
2. The type of lighting used is therefore dependent on the animals kept. Generalizations do not work most of the time, even though many hobbyists would like to receive such recommendations. Watts per gallon may sound an appealing way to make recommendations, but it is not a real accurate way to go about it. We often use it in the hobby because it give hobbyists some idea of what kind of level of intensity we are talking about, but it is not an accurate way of looking at lighting.
3. The depth of the tank has not much to do with what kind of light you need to use. What is imporartant though is that, if an animal that requires a lot of light is placed at the bottom of a deep tank, the power emitted by the light source used, will need to be far greater than in a shallow tank or the desired energy levels will not be achieved. This should be quite obvious.
4. If, however, we place an animal in the same tank that is low in energy requirements (lighting defined as "photon" irradiance ... gee there I go, I used the "p" word) then a totally different scenario comes about and we do not need that much intensity to provide that coral with its required photon irradiance (which in turn determines the level of energy the coral can derive from that light source).
5. Photon irradiance is the real manner in which the amount of energy a coral (in this case) is exposed to and can "absorb and process" should be looked at. It is, however a complex matter and not within the scope of most hobbyists, at whatever level of expertise they have arrived. Not that they cannot understand the concept, on the contrary. The problem would be how to calculate the amount of watts required based on the photon irradiance needed by a coral, given that the latter is influenced by many factors, as we shall see.
6. Photons and Quanta, and various other related ways to look at lighting intensity and energy are very complex, to say the least. It takes a real thorough understanding of "light" and I am not sure we want to go into it, here, as it IS truly very complex. I will give you a real good reference book at the end, if you are interested in reading up more on the subject and looking at the mathematics behind it all.
7. Just briefly : light refers to the behavior and intensity of light in natural seawater and and in the water in our aquariums (and the two are not the same) !! The factors influencing the intensity and wavelengths are totally different in aquaria than they are in nature and so are the light sources we are comparing (the sun vs bulbs to state it simply).
8. Light is, in this case at least, the radiation in that segment of the electromagnetic spectrum between 400 to about 700 namometers. That range includes the blues, and the other wavelengths needed for Photosynthes I and II cycles.
9. It is interesting to note that the breadth of this band is very much in the width of wavelengths that the human eye can perceive, hence the risk for greater confusion, as we sometimes think "the more intensity the better", forgetting that corals do not perceive light as the amount of intensity, but as the amount of energy they derive from it (the more photon irradiance on a particular coral, the more energy is that coral exposed to). Some corals may in fact not need all that much light energy. Some do and some don't as we all well know.
10. The behavior of light is greatly influenced by the medium it passes through, as the media affect both the wavelengths and their intenties (reducing them of course). Whereas air as a refractive index that is close to 1 (actually 1.00028), water and especially salt water has a far higher one, on average around 1.33.
11. This of course influences the end amount of light energy one exposes the corals to as the loss from traveling through air is one, but the far greater loss of traveling through water is the major one. This is influenced as well by salinity, temperature and turbidity.
12. Light, electromagnetic radiation of a particular kind, behaves in the form of a wave (hence wavelengths). The type of wavelength determines the energy contained in the particular light band. The shorter the higher, and the longer the lower the energy is. That is why blue light has more energy than say yellow or red.
13. Thus, a small amount of short wavelength light can only be duplicated with far more intensity of longer wavelength light (note this as it explains why increasing the intensity of one type of light can bring about the same results as a far lower amount of another type). The bracketed procedure is not recommended but often used. Stash as many lights over your tank as you can, disregarding the type, and all animals should do well. Not really.
14. Energy is expressed in Joules, which through some real fancy calculations beyond the scope of this "chat", could actually be converted to watt. Unfortunately not across the entire spectrum though but just across narrow ranges of it. This is described in great detail in the book I recommend at the end of this "chat".
15. What you should know though, is that the energy originally given off by any light source is reduced to a great degree by distance from the water and by penetration into the water and by anything that may be placed between the bulb or light source. The bulbs' glass shield itself causes a reduction as well. Humidity does too. Dust does, etc.
16. Now on to Corals. Some require real high amounts of energy, as they are strongly photosynthesizing. Such corals will require more energy and will only do well if that energy level is provided. It can be provided in two ways that are obvious : a certain amount of short wavelength light or a far larger amount of longer wave light. The latter is not the best way to go though, as indicated earlier.
17. This explains why when using light with high amounts of actinic (short) output, not as much is needed as when one uses a light source that emits a far higher wavelength (e.g regular fluorescent tubes). In the first case only a small amount may be needed whereas in the second case a far greater amount will be required to achieve the energy levels that particular corals are in need of.
18. Not all corals require the same amount of energy of course. That is where our problem comes in. What is plenty for one, may be not enough for another one, and may be too much for yet another one. Requirements are coral or animal specific. Many may be close to each other in terms of requirements (good for us), but others are not. Knowing the difference is important.
19. Knowing lighting requirements helps a great deal therefore, and allows us hobbyists to place corals in positions within the aquarium where the amount of light they receive is closer to what it should be. Low energy requiring ones towards the bottom, medium ones towards the middle, and high intensity (energy) needing ones towards the Top. Some corals with real low energy needs may even need to be shielded so they are not overexposed to energy (and close up before the photoperiod over your tank is ended).
20. As you can see, there are so many variables to deal with that it is difficult to satisfy them all and hobbyists, therefore, end up having to compromise and use a middle of the road approach. It is not possible to "really" optimize light (energy) for all corals in your tank. This would be possible though if you had a species aquarium and knew the requirements of that species. 21. Depth is really irrelevant to a great degree, unless you plan on placing corals that require a great deal of intensity at the bottom of the tank (in which case the ones that are higher up in the aquarium may either receive too much energy and close up early in the day, or may receive so much that they are damaged in the process).
22. Again, knowledge of the amounts of intensity and the type of wavelenghts such corals are exposed to in nature helps a great deal. This is covered in detail in my new book The New Marine Fish and Invert Reef Aquarium (expanded version) which will be out finally in the fall. If you want details on the contents you can send me email at email@example.com.
The cost for pre-payment of the book is $40.00 versus the retail of $90.00, and if you prepay you also get a free electronic version with more photos. In addition the electronic version will be updated from time to time to bring you the latest changes. To order send me email as listed above.
23. Let us deal with yet another concept : direct and indirect light, or direct and reflective light. This is another important facet to look at when deciding where to place a particular coral. Elegance coral, for instance, is often found under overhangs and receive only reflective light (but strong) not direct light. The ones that have lots of green zooxanthellae are the ones that receive direct light of great intensity and the ones that do not are the ones that receive less energy from light and receive it mostly in the "reflective" form.
24. Generalizing is very difficult and tricky, but is unfortunately what we all have to do in tanks that contain corals with various, and differing, energy requirements. We do not really have a choice. We try to achieve the best for all corals, and newer bulbs allow us to provide energy output that is closer (but still nowhere near) to what the high photosynthesizing corals require. We need to be careful though not to overexpose those corals that have low lighting requirements. Knowing requirements through reading, and then applying that and positioning the corals in certain areas is the key to success.
25. I know that you will have many questions and hope that I can give you answers that make sense. No one, in my opinion, has all the right answers, more so even where it comes to lighting and the energy derived from it by corals and other animals in the aquarium.
26. For those of you who want to really get into this in depth I recommend the book: "Light and Photosynthesis in Aquatic Ecosystems" by John O. Kirk (Cambridge University Press - around $70.00 for the full version - 400 + pages of highly highly technical material on the subject. BTW the book lists 561 additional titles you could read or refer to, if you wanted to have all the information.
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