More On Lighting

(PART-1)

ARTICLE by Don Carner

Introduction to Fish-Only Tank Lighting

A wide range of articles on this topic can easily be found in most marine aquaria publications today, but all the information discussed here is based upon personal observation and implementation. With the information that I am going to share in this series on saltwater aquarium lighting, I hope to help you learn how not to drive yourself insane, broke, or both! Having said all that, let's begin.

There are many variations of marine life keeping now popular in this country and abroad. For the sake of simplicity, I will categorize this article into the two major subdivisions: fish-only and reef lighting. Naturally, any lighting package suitable for a reef system would also be useable on a fish-only tank, but it would be rather like hunting squirrel with a stinger missile!

Seeing as how the majority of folks entering the hobby begin with fish-only systems, I will address this area of lighting first. Many of us who contemplate getting started want to begin with the idea of upgrades and expansion down the road, or after "getting their feet wet". This is wise, as it is always preferable to over-compensate in our hobby. Why? The primary consideration is cost. Better to buy that which can be reused or recycled later when that bigger tank and more delicate species catch our eye.

The basic fish-only aquarium set-up usually consists of the tank, filter and lighting. There are many other factors to consider, but for my purposes of addressing aquarium lighting here, I shall keep it simple.

Pre-manufactured plastic hoods with a single or double fluorescent tubes are ready-made packages that are easiest to install and maintain. You have no options here. Buy it, set it on the tank rim and turn it on. The quality of the actual tube is generally geared for freshwater guppies and goldfish, rather than marine fish. Not to worry though, as there are essentially no differences other than color enhancement for the viewer.

If you are amongst the majority of first-time aquarists, you will most likely choose a package or light hood that is recommended by your local fish shop. These packages normally consist of the one-piece plastic hood with the light fixture already installed. The ease and convenience of these light hoods are very attractive to the beginner as they require no specialized knowledge other than where to plug them in! By simply installing these hoods on the tank, we have accomplished and eliminated all the worry and frustration over what to do about illumination. This frees the aquarist to concentrate on the learning of other basics that ultimately result in long-term success in their new hobby. These hoods use a "can" electro-static energizer to get the bulb glowing and are easily replaced when they eventually go bad. Plastic hoods, while not cheap, certainly provide all the fundamental requirements needed for the first time fish-only aquarist or long-term fish-keeper.

Fluorescent tubes provide varying degrees of color enhancement to the fish, that results in the gorgeous splash of vibrant colors that attract most new folks to the hobby. The basic wattages in standard "stock" tubes here vary from 15 watts to 40 watts output power. Newbies will soon learn that tube length generally equates to tube wattages, although we shall see how this can differ as we progress. For those wanting a small system up to 55 gallons, and have no intention beyond fish-keeping, these plastic hoods with their Standard "stock" or NO fluorescent tubes do a fine job and provide many years of reliable service. NO (Normal Ouput) fluorescent tubes like the Vita-Lite feature a color temperature around 5500K and come with a stated useful lifespan of approximately 20,000 hours of illumination. They also have a two-year warranty that make this choice ideal for the fish-only set up. The beauty here is that these NO tubes are quite reasonable in price and the experimentation process can be fun and stay well within a reasonable budget. However, they will not be able to accommodate nor support any photosynthetic animals, or provide the output intensity required for other extremely light hungry marine denizens.

What is to be expected and what is to be accomplished by these hoods is simple and straightforward. Basic illumination and the simulation of the day-night cycle as found in Nature. By replacing the stock tube that comes with these pre-manufactured light hoods, one can influence the coloration of the fishes and other aspects of the aquarium’s environment.

What if your plans are to start out with a fish-only tank with no intention of keeping reef animals, but later change your mind and decide to advance into the realm of keeping some reef life? The question here is, will a basic pre-manufactured light hood work for this purpose, and if so, which type should you choose?

For those of you contemplating a 55 gallon aquarium as a fish-only tank to begin with, and choosing say a Perfecto style plastic hood, try to select the model that incorporates 2 tubes. Why? Sooner or later, and it happens to most fish-only aquarists, you are going to want to try “just a few†soft corals, or perhaps a piece or two of live rock. The flexibility that the 2 bulb fixture allows is to be able to replace one of those standard lower wattage and "K" (Kelvin) stock tubes with an actinic, or a higher K (Kelvin) NO tube, such as a 10,000K bulb. This will allow you to accommodate some reef life. I go into more detail about specific reef life lighting requirements in later Chapters, but for now keep in mind that only the very hardiest of soft corals, such as the actinodicus (mushroom corals) and sea mats can thrive under the illumination provided by only two of these normal output tubes.

As we progress into the understanding of fluorescent tube wattages, CRI and "K" (Kelvin) in Chapter 2, you will see how by experimenting with the various types of lighting tubes on the market, the hobbyist can discover the myriad of differing effects these lights can achieve. Testing the waters in this manner allows the hobbyist to get their feet wet in the realm of invert and coral keeping.

For a beginning introduction to understanding reef aquaria lighting, let us take a look at the basic types of lighting methods that can be used.

Now that I have addressed the basic lighting requirements of a fish-only tank, the reef aspect to aquarium lighting is a much more complex and intimidating arena. Before I begin on this discussion, let me state right up front that each element has its supporters and detractors. There are just as many pros and cons and opinions as to "what's the best lighting to use" as there are to the politics of this great land of ours, so be forewarned, I'm sure I'll ruffle a few feathers here! Follows is a basic outline of the various types of lighting used for reef aquaria.

1.) Fluorescents

A - Normal Output (NO)
B - High Output (HO)
C - Very High Output (VHO)
D - Power Compacts (PC) or Osram

2.) Metal Halides (MH)

-Metal Halide does not have any differentiating qualities other than wattage and spectral output.
-Sodiums and Iodines are not suitable for our hobby, so I'll state that commercial building or parking lot metal halides be steered clear of.

Now, why choose one fluorescent over another? Why choose fluorescents at all? Why not go for it and install metal halides? Or for that matter, why not pick up a power compact and leave all the controversy behind? It is these very questions that plague many hobbyists. Most of us plan on spending and investing in a lighting system only once, and want it to be right the first time! I shed a little more light on this very issue in PART-2, discussing in detail the fundamentals of fluorescent lighting such as wattages, the CRI (Color Rendition Index), and "K" (Kelvin).

(CONT. PART-2)

 

Part-2

(cont. From Part-1)
LIGHTING FUNDAMENTALS

In my introduction to saltwater aquarium lighting, in PART-1 I talked about the requirements for lighting a fish-only tank. At the end I began discussing reef aquaria lighting, and provided an outline of the basic types of lighting methods that can be used on a reef system. Since the bulk of reef hobbyists begin with recycled freshwater hardware or introductory marine equipment, I'll first explain the basic fundamentals of fluorescent tubes so you can better understand how they function, and what purposes the various types serve. By understanding these important factors about fluorescent tubes, you will better understand how they will relate to reef lighting as we proceed. Once more allow me to explain that I will undoubtedly ruffle feathers and cause an occasional guffaw. Occupational hazard, let's move on.

Interestingly enough, I have encountered far more hobbyists that are focused on the hardware more so than the actual animals that all the fancy nomenclature is designed to support. I will not get into the, "what's the best lighting - who's makes the best bulbs", etc., etc., etc. However, what I will do is point out which types of tubes/bulbs/lamps are best for varying conditions or targeted environments. This, after all, is the reason for their ultimate being!

In defense of those folks that want "the best or latest", I applaud your conscience effort to afford your wet-pets with the finest that your money can buy. You may see that you can accomplish similar results spending far less than normally expected. Maybe not as sexy, but definitely effective.

Essentially, fluorescent tubes are the most practical and most cost effective of any lighting source. They burn relatively cool and last many months. What one must watch for when choosing these tubes are their wattages, and CRI (Color Rendition Index), also referred to as "K" (Kelvin). Let's begin with wattages.

-The Reef System Wattage Rule of Thumb Formula

The general rule of thumb for a reef system calls for 3 to 5 watts per actual gallonage of water. A classic example of this is best visualized using the industry standard, a 55 gallon glass aquarium.

Using the above "Rule" this reef should have a minimum of 165 watts to 275 watts in order to provide the intensity necessary for photosynthesis to take place within marine organism's polyps or tissues. Here are few more examples of reef system wattage requirements using the "Rule".

-3 to 5 Rule of Thumb Formula Examples
3-5 Watts X 55 Gallons = 165 to 275 Watts
3-5 Watts X 75 Gallons = 225 to 375 Watts
3-5 Watts X 150 Gallons = 450 to 750 Watts
From these simple examples you can see how easy it is to determine the wattage requirements for your particular reef aquarium needs.

-Understanding Tube Wattages, NO vs VHO

Longer length tubes yield higher wattages. To better understand tube wattages, look at the comparison chart below. You can see that the wattages increase with length, no matter which type of tube it is.

Now compare the wattage of the NO (Normal Output) or Standard tubes to that of VHO (Very High Output) tubes. The wattage ratings on the NO/Standard tubes are much lower than that of the VHO tubes of the same length.
"T" Tubes
Normal Output (NO)
or Standard Tubes 18" (T - 8) = 15 watts
24" (T - 8) = 18 watts
24" (T-12) = 20 watts
36" (T-8 & T-12 )=30 watts
48" (T - 8) = 36 watts
48" (T-12) = 40 watts

Normal Output (NO)
or Standard Tubes 36" = 30 watts
48" = 40 watts
60" = 58 watts

High Output (HO) Rarely used anymore,
and difficult to find commercially.
(Requires special ballast)

Very High Output (VHO) 36" = 95 watts
48" = 110 watts
60" = 140 watts
(Requires special ballast)

As you can see, instead of having to use 6 - 40 watt NO tubes, you can achieve the same or similar results by using just 2 VHO tubes. See why VHO's are the industry standard in reef lighting? The actual number of tubes necessary to achieve that "3 to 5 Rule" makes VHO's a natural!

Fluorescent lamp labeling, such as that of the basic stock NO tube widths of “T-8†(skinny) and “T-12†(fat) can be confusing. All this means to us is that the physical size of the fluorescent tube must match the hardware for which it was designed. Rarely can you replace a T-12 in a T-8 fixture, it just won't fit! That's all these “T†designations refer to, the diameter of the tube. Generally, smaller systems and their corresponding hoods use the T-8 diameter bulb, while the larger units have the elbow room for the larger T-12’s.

Using off-the-shelf lighting would dictate 4 to 6 tubes spread out over the open top of the tank. Open? Absolutely! I don't know of any hood manufacturer that makes a rack that accommodates 6 fluorescent tubes. I've seen many, many 4-tube racks, but why settle for minimum? Maybe the manufacturer's know something we don't? Maybe that something is known as HO (High Output) and VHO (Very High Output). By using these types of "booster" tubes, wattages far in excess of NO/ Standard tubes, fluorescents make packing intensity into tighter and smaller spaces a reality.

-VHO Ballast Requirements and Lumens
An important factor when choosing to use VHO lighting is that one cannot simply buy a VHO fluorescent tube to replace the stock 40 watt bulb that came with that Perfecto hood you purchased!

VHOs require special 1500mA ballasts or ballast kits, and are not compatible with any other ballast. Oh sure, it'll fire up, but why? Your output will be the same as that $2.00 Growlux bulb, so don't succumb to that thought!

1500mA? mA is the ballast amperage rating, and I refuse to get into basic electricity theory here, LOL! We can discuss ballast at another time. The point here is that once you make the conscience decision to upgrade to reef lighting, VHOs are the natural first choice. Cheaper and easier to install, they form the backbone of the hobby's lighting regimes.

What are Lumens?

Lumens is another area of common confusion. Wattage is the "power" of the tube. Lumens are the actual amount of light being "radiated", or the amount of light energy reaching the animals created by the power output of the tube. Wow, now I'm confused!

Actually, let's equate it like this: Consider a shotgun blast. The number of pellets or "shot" that reach it's target is directly proportionate to the muzzle velocity of the gun that is it's source. The magnum shell will deliver more shot to it's "target" than a regular or low-brass shell because of the muzzle velocity. So does the VHO tube over the NO tube. More LUMENS, (or "shot") reach the animals (or "target") than an NO tube, because of wattage (or muzzle velocity). So LUMENS equal the light energy that WATTAGE delivers! This is naturally a gross over-simplification, but I think it works.

-CRI, or Kelvin

CRI is the manufacturer's gauge for the type of light that the tube emits.Type of light? Sure! Did you ever notice that warm white looks yellow compared to cool white in your kitchen ceiling fixture or over your workbench?

This is due to the formulation of phosphors used during the construction of the tube. See how color temperature relates to the "warm white" and "cool white" labels? All well and good for your office or home, but not nearly good enough for our corals and inverts! Hence we rate our tubes by K, and that other thing known as wattage. K stands for Kelvin, or the color temperature, another confusing term for CRI. As a general rule, aquarium related fluorescents in regard to reef habitats should not fall below the 5500K rating.

Please keep in mind that different companies use differing terminology for the same thing. CRI, K, Spectrum, Color Temperature, etc., all refer to the type of light their products produce. Actually, there are sound reasons for using differing names or labels, copyrighting being amongst the most common. Just like car companies use "4X4" or Quad Drive, it still means the same thing!

Basically, and without getting into a deep science seminar, the lower the Kelvin, the more yellow the light. Hence, the higher the Kelvin, our light appears starkly white or blue-white. Getting way up there into the 20,000K range, the bulbs actually appear to glow dark blue! Shades of the blacklight craze! Oh no, don't EVEN go there! Blacklight has tons of that nasty ultraviolet, and our animals don't like that at all! Save it for the bowling alleys or fuzzy posters!

-Exploring Kelvin Ratings Further

Let's explore Kelvin a bit further by taking a look at various K ratings, and the reasons for using them.

5500K
(Bottom end of acceptable CRI)
Reason: Frequencies below 5500K promote algae blooms as these algaes prefer less blue-white light and lean to the red-yellow absorption spectrum.

6500K
(Middle of the road CRI)
Reason: Best all-around starter frequency, often used in conjunction like the
5500K series, with actinic blue tubes.

10,000K
(Upper end of the advanced or special-need frequencies)
Reason: Incredible amounts of deep-penetrating blue-white light, making
them ideal for deeper tanks and simulating deeper reef environments.

20,000K
(The upper end of deep water simulation)
Reason: Because we can.

Actinic
(420 nanometer wave-length or frequency)
Reason: All corals and most inverts absorb light at the blue-end of the frequency curve far easier than at the red or shorter end of the frequency curve. Actinics are mandatory when using frequencies below 10,000K. Think of actinic blue tubes as "boosters" to be used in conjunction with the regular
55-6500K range of bulbs. It's the blue light that really makes the difference in
photosynthesis, and more is better in an aquarium!

(CONT. PART-3)

 

Part-3

(CONT. FROM PART-2)

-Why Are Differing Kelvin Ratings Necessary?

Why are differing Kelvin ratings necessary at all? In a word, DEPTH! The natural reef environment begins at the surface and can reach to depths down to 150 feet, or more!.

If you have ever snorkeled or scuba dived, then you're aware of how quickly water depth can effect light intensity. The lower one goes, the dimmer and darker the light, turning from turquoise to azure to cobalt in very quick order. This obstacle haunted the hobby in it's infancy until Philips and other tube manufacturers realized that there was a dollar or two to be made in this hobby! Once it became economically feasible, tubes strictly for our tanks suddenly began appearing in magazines and our stocklist shelves. Holy reef tank Aquaman, I can now keep that once delicate specimen thriving in it's little glass box for more than a month or two!

Seriously, the K rating, or CRI, gives you the ability to match the tank lighting to that of your animal's natural habitat. Without this important advances in the industry we could never hope to duplicate lighting conditions at DEPTH in our living rooms, and provide as near identical conditions for our corals and inverts as that in nature.

Now wattage plays a part here, too. The higher the wattage, the deeper it will penetrate. With the right K rating though, a hobbyist could conceivably duplicate conditions at say 50 feet in an aquarium only 18" deep. It's a trade-off, higher wattage vs. proper K rating. Combine the two and you achieve reef lighting Nirvana! Why go there? SPS corals, for one.

SPS corals? I know, I know! You want to hear more about this topic in detail, but for now it is more important to deal with the other various methods of achieving proper illumination for your reef tank. By knowing all of the reef lighting options available, when the time comes for you to purchase your reef lighting system this information will assist you with making a wise choice. Now let's go on to PART-3 where I talk about reef system light choices, such as using pre-manufactured light hoods, MH (Metal Halide) and PC (Power Compact) lighting. Once done there, then you can go on to PART-4, which deals with the specifics of coral lighting.

-What To Buy & Why

Let's stop and review. In PART-1 I addressed fish-only tank lighting requirements, including using pre-manufactured light hoods for these types of tanks, was well as the possibility of using them for keeping "some" reef life.

In PART-2 I covered the basic fundamentals of NO/Standard and VHO fluorescent tubes, such as how CRI or Kelvin determines a bulb/lamp's color frequency, how wattage is beneficial and why it's important, and fluorescent tube wattage comparisons. Depth simulation has also played a part in our lighting selection process.

Now that we have a better understanding of the basic principles of aquarium lighting, and the various methods by which they are presented to the hobby, we face the ultimate decision of what to buy for a reef system, and why?

O.K., remember how I said that each company likes to tout its product as the savior of the marine community? Well, I can tell you that you will have equal success with fluorescents as well as PCs (Power Compact fluorescents), MHs (Metal Halides) and power stars (a differing bulb manufactured than standard MH). Marketing is nowhere more dominant than in this hobby.

-The Light Manufacturers' Marketing Game

The consensus is that if you have the disposable income to even THINK about setting up a saltwater aquarium or reef, then you have enough to plop down $495.00 for a powder-coat, German tensile steel light bar that looks like it came straight off the space shuttle! Actually, for my first three years in the reef community I used Ultra-Lume 75’s and actinic light tubes. When was the last time you saw Ultra-Lumes advertised? Not sexy anymore. The fact that they work is irrelevant. Marketing, remember? Ask the folks that own Cyclone skimmers about advertising vs. performance and you'll begin to see my point. Now please, don't get me wrong. I like my toyz as much as the next person, but think of how many more you can possess if you keep the second most expensive addition to your marine set-up, under control.

That's right, a VHO package isn't cheap! Metal halides are even costlier, not to mention that steel light bar I mentioned a bit ago. Choose carefully and plan ahead. Look toward the day when you wake up and WANT to cultivate SPS (Soft/Small Polyped Stony) corals, or the like. Unless you know that this isn't in your aquarium future, stick to standard fluorescents and spend the savings on upgrading or buying a great skimmer, not just one that you can afford now. Skimmers? Maybe a future article, but not here and not today. LOL! Right now I am going to have a serious discussion about using pre-manufactured light hoods for lighting a reef system, which is NOT a good choice!

-Using Pre-Manufactured Light Hoods on Reefs

Let me start out by stating right up front that plastic, pre-manufactured light hoods are NOT acceptable on a reef system. Besides the obvious, the design limitation on using HO (High Output) or VHO (Very High Output) tubes, these hoods cover 95% of the surface of the tank. This leaves little room for overflow boxes, powerheads, hang-on skimmers, etc. Also of serious concern is the restriction that a full enclosure at near-surface level creates on oxygen gas exchange. This is a biggie with me, and should be with others as well. Reef tanks should incorporate "open-air" or have unrestricted access to the entire water surface area. Not only does this allow for freedom of movement for moving/adding and feeding, it also allows for the best gas exchange between the water surface and the room's atmosphere. If you MUST cover your tank top, use eggcrate available at Home Depot and the like.

This will allow for air movement, easy access for adding rock, corals and animals, as well as keeping those "jumping" fish from performing Hari-Kari onto your Oriental rug. Did I mention that plastic eggcrate is just about the most versatile of all the accessories that a saltwater enthusiast can have? No? Well, shame on me! Not only does the eggcrate keep your fish where they belong, it also acts as a support for your fluorescent light tubes!
Oh, please DO NOT use eggcrate when running metal halides. Let's just say that I upgraded once upon a time from VHOs to a 250 watt MH and forgot to remove the eggcrate. Honestly, it took me a few minutes of staring at the white stalactites that had miraculously appeared while I was at work before I realized that my lamp had melted the eggcrate! Those metal halides sure get hot! This leads me into my next topic of discussion, the pros and cons of using metal halides.

-Using Metal Halides

If I seem to dwell on VHOs, there's a good reason. While metal halide (MH) lighting is the finest light energy source we have, and it can provide the right incredible intensity of light ideal for maintaining delicate to establish SPS corals, they create all kinds of other issues to the aquarist. Metal halides are essentially a very powerful incandescent light bulb. Touch a 100 watter in your living room lamp and you'll see my point. Now, magnify that to 175 or 250 watts and you begin to see the impact on water temperature. Maintaining water temperature at or as near to 76-77 degrees is problematic enough. Hang that heat-radiating bulb six inches above the water surface and watch your tank temperature climb, Climb, CLIMB...

Fans, chillers and building special hoods to accommodate MHs are but a few of the residuals that using these bulbs can create. If you are not willing to shell out $500.00-$600.00 for a commercial chiller, then using fans mounted at the water surface or in the hood are your only avenues of keeping the water temp within limits. Ever hear of the domino principle? Fans cool the water by evaporation. If you are replenishing a quart or two a day due to ambient evaporation, just wait till you kick that fan on! Doubling or even tripling current evaporation rates can be realized when using cooling fans.

One thing DOES lead to another here, doesn't it? Did I mention special hoods for MH's? Yep. A 12 inch MINIMUM distance from the MH bulb to the water surface is the rule. This allows some air movement between the bulb and the water, lessening the heat impact. Still gotta use those fans, though!

So if VHOs aren't conversationally correct for your project, and metal halides aren't practical, what other avenues do you have? Power Compact (PC) fluorescents are the answer.

-Using Power Compacts

Actually nothing more than a straight tube bent in half, compact flourescent lamps deliver a higher concentration of light energy in a smaller space than standard-length tubes do. Their VHO nature gives them the ability to deliver the right amount of lumens in whatever color temperature (CRI, K., etc.) you choose. I ran a 20 gallon long on 6-9 watt compacts for three years. One 9-watter is equivalent to a standard 75 watt incandescent, so you see my little tank was well illuminated! Yeah, I had SPS frags in there, too.

(CONT. TO PART-4)

 

Part-4

(CONT. FROM PART-3)

-Introduction to Coral Lighting

At the end of PART-3 I mentioned SPS corals and the necessity for proper CRI and intensity. First and foremost, most corals can be placed into three major catagories: Stony (exterior skeletons), Soft (no calcium-based skeleton), and SPS (Short/Small Polyped Stony). Naturally, the scientific world can catagorize these animals down to the "inth" degree, but for our purposes these three categories will suffice. When it comes to how corals grow, each category of animal requires its own unique lighting requirements, but all share one common trait; photosynthesis in order to survive. Just as plants convert sunlight to produce chlorophyl, marine animals survive similarily by converting light energy into "food". Actually, this energy is consumed by zooxanthellae algaes that produce by products that the corals need to survive; a true symbiotic relationship.

-How Changes in Lighting Effects Corals

Coloration of coral polyps and tissues is dictated by these zooxanthellae. By differing the spectral output of our tank lighting we can actually influence the ultimate color/shading of our corals. How? Let's say that we have been using a 5500K VHO flourescent setup at 220 watts. We get that itch to spend money and help our tank and animals by installing a 250 watt metal halide with a 10,000K lamp. Aside from the asthetics of the rippling light show these lamps provide, we have suddenly changed the frequency of light that all the animals in our system have grown accustomed to. I use the term "frequency" to describe the change in CRI or spectral output. Often, the corals will shrink up, close their polyps, or otherwise show their displeasure at this sudden and drastic change in their energy source.

It's actually the billions of symbiotoc algaes that are recoiling, sending shockwaves through their host and causing this rapid change in appearance. Within days, and sometimes even hours, the zooxanthellaes will adapt to this new frequency and intensity by changing their absorption capabilities or their overall color. That's right, the coral's color is actually that of their hitch-hiking algaes, adapting to the increases or decreases of ultraviolet and other energy-source factors. Have you ever looked at a Tridacna clam from the top of the tank, then lower your gaze to a sideways view, only to be disappointed? Strange how dull the clam's color appears from the side, while from above all those rich and vibrant colors seem to shout at the sky? Well, that's the clam's zooxanthellae algaes, doing their thing, protecting the clam's delicate tissues from sunburn!

-Avoiding Sudden Changes in Lighting

Whenever a change in lighting takes place, and don't be fooled, even replacing old tubes/lamps with the exact same wattage and URI can create the same response if the old tubes have been allowed to degrade past their useful spectral output, the system should be allowed to gradually adjust to this major change. How? I ususally replace lamps and tubes just after the system shuts down for the night. I then replace or exchange old for new and insure that next morning, not all the lights kick on at the same time, allowing intervals between pairs or types of tubes. If you have only a two-tube system this isn't possible, but the installation of a dimmer circuit like ones found on some electronic ballasts, makes the chore much easier to accomplish. Remember that corals and their zooxanthellae adapt to changes in their surroundings the same as we humans do. Where as we may shade our eyes from bright sunlight, these animals have no such luxury. They must react as only they can, by recoil and a slow but gradual return to normal behaviour. Interesting how we can't discuss lighting without getting involved in the coral's actual physical properties, isn't it? Well, afterall it IS the primary reason for lighting at all!

-Lighting For SPS Corals

SPS (Short/Small Polyped Stony) corals are by far the most numerous in the skeleton catagory. I will not delve into the physiology or other biological factors of these corals, other than to state that they, above all others, require the most dynamic of light sources. Not until the advent of aquarium related halide lamps was this light source truly ready for our use. The incredible intensity of the metal halide lamp makes providing the right output of light ideal for maintaining these delicate-to-establish corals. Once they grab hold, SPS corals can be the most prolific of all their kind, growing at enormous rates and prompting many cuttings. These coral cuttings, known as frags, can then be propagated through "coral-farming", which is highly practiced by many hobbyists and commerical aquaculturing companies today.

Naturally, factors other than the lights themselves contribute to the success of any coral, but once the water parameters and the lighting system are acceptable to the animals themselves, watch out. LOL!

END.