sorry for the errors but my ocr is not the best
sorry for the errors but my ocr is not the best
From cars to sports teams to politics, there are some topics that just invite spirited discussion. For reefkeepers, lighting is the
topic that invariably galvanizes any reef tank discussion. Lighting is one of the most hotly debated aspects of reefkeeping because it is one of the most misunderstood. Much of the debate is fueled by misinformation, and thus misguided conclusions, about the role that light plays in coral health.
Debate regarding reef tank lighting has been going on for as long as the reef hobby has existed. Before the 1980s, however, the available lighting options were rather limited, so there were few aspects of lighting that might create the level of passionate debate we see today. Vntually all hobbyists used fluorescent tubes to light their tanks, and the debate was limited to
which of a handful of lamps =best-looking reef tank. The ~ sensus of the day was that a
of "daylight" tubes and actici;: vided the best balance of !ms--r and a blue cast to bring out ~ the reef tank. The overall bbe
mix hid the yellow cast of reef 2!DI: The near-ultraviolet light O:;Z bulb made many corals flUORS.::.
In the late 1980s, North .!. keeping started gaining
hobby was demonstratingm_
ill creating a healthy envi.~ tank inhabitants, and more
we were beginning to be-""e!'
which critical elements prOOa;=t
successful tanks. Hob~ beginning to create 1argc:::. tems, and they found that -;;'~-l!
rescent tubes did not ~ tanks very well.
Aquarists started experimenting with metal halide lamps for these larger tanks. It soon became clear that while metal halide bulbs presented some challenges, they also offered some definite advantages. At the time, the only commonly available metal halide bulbs were 175-watt bulbs with a low color temperature of 5500 degrees Kelvin (K). These bulbs, manufactured in the U.S., created an unattractive, washed-out, yellowish-looking reef tank, but at least the tanks could be larger and deeper.
Reef tank lighting was beginning to advance, but the gains were made mostly through trial and error. The hobby had little real lighting data that might help explain why some bulbs performed better than others. Some limited intensity numbers were available. There were even crude spectral charts for some of the bulbs, but the debates over them were pretty calm by today's standards. By the early
1990s, the hobby had fully embraced metal halide bulbs, and with few choices there were few things to argue over.
A BREAKTHROUGH
Then a few aquarists discovered a German-made 40Q-watt metal halide bulb with a strong blue cast and a reputed 20,000K color temperature. Hobbyists begari hand-carrying small numbers back from Europe, and soon there were networks of cutting-edge reefkeepers using this bulb. Online discussion groups, such as Fishnet, were also gaining in popularity during this time, and word of the new bulb spread quickly.
The bulb was a turning point for reefkeeping in two respects. First, it seemed to be a significant improvement over the bulbs hobbyists were using at the time. Reefkeepers seemed to have the best of both worlds: the high intensity of metal halide
lighting combined with the aesthetics r£ orescent lighting. The application of a'. temperature metal halide to reefk~ significant because it was one of the =-""'breakthroughs for the hobby that sprea.: _ through online word of mouth, as large hobbyists simultaneously learned of r_
The debate over lighting was h~ ~ i because the hobby was gaining new ~:
i because we could debate the merits o~ ~
;
i with thousands of hobbyists through~ :2 i At the same time, increasing numbers ~ _ ! were finding that the coral reef scientific
i could help us become better reef hob ~
..i those of us reading the scientific ~
~i sharing online what we were finding_
~! In 1995, I was one of the earliest ho~
ill experiment with this bulb, and like ~ :: ~
my reef tank responded positively. T'"~ ~ -response, however, was short-lived. ..!. ~~ . months, coral growth declined, and I W'"'.,.s b:1 switch back to the 6,500K bulbs I ~ -
Other hobbyists had similar experiences weren't quite sure what was happening. iiF.: only speculate about possible reasoLS.. : tests on the bulb along with other popu:.c
the day. My results were ultimately ~
1997, thus becoming the first comp~ at metal halide bulbs. An Adobe Acroba: ~ _ the article is available at
www.r~
Since that time, the numbers of mea. bulbs available to hobbyists has increaser stantially, and authors such as Sanjay;~ others have built on my initial study. ~ more detailed analyses of large num~ ~ halide bulbs, ballasts and reflectors. 7~ hobby is awash in lighting data.
We now have information on lighting nents that could create well over a thO!!SZllt ferent metal halide lighting systems. Yet
the additional information, the hobby has =a: any significant advances since this flood ::t mation began. All the tireless efforts ~ .: reefkeepers with more information has DOC better as aquarists. The additional ID:'
does not seem to have had any practical ~
our ability to create healthy reef tanks oc animals that we might not otherwise ~ really are no further along than we were ::: ~ ago. And thus the debates continue.
The data have failed to resolve the ~
the fact that one can measure a parameta' automatically make the measurement ~ a more precise measurement of an parameter does not make it more imponz::::.. ~ than collect as much lighting data as p<~",7...
should determine which measurable dz:z. wi[
"at we need to know to create better reef
Ik5 :n what follows, I will identify aspects of kri::g that are important for a reef tank and Ilore the fundamental issues that need to be ier.;rood before one can properly judge the value I m:ility of the lighting information available to , hobby.
;tiT ON THE NATURAL REEF
rr.e critical role of light in determining where lItDSyIlthetic corals are found in nature has been iIerstood since the 19th century. By the early II:. century, scientists had discovered the symbi~p>.Jationship between algae (zooxanthellae) and lit corals, which required corals to live in shalF_ :mghtly lit waters. In the 1970s, scientists F experiments that ultimately proved a direct
k between light intensity and coral growth - the
-=er the intensity, the more rapid the growth. D: these early studies, scientists have learned ~t deal more about coral growth and light msity, but broadly speaking, the early groundrakmg studies from the 70s and 80s are the most tical in understanding the relationship between Ii and coral health.
~ a certain intensity, light levels are not sufier::: :0 support photosynthesis. A coral mainIerl below the "compensation point" will gradur Gie.. Light intensities greater than the com~ point facilitate photosynthesis and coral r.h., As light continues to increase, photosyn' 55 increases, as does coral growth. If light ~ is too great, zooxanthellae become satueC with tight, and no further increase in photoIL::.esis occurs.
Ie knov,r that corals can grow up to the surface ttc ~ter, and we know that growth slows at ~ depths until light levels decline to a point ~ r;uwth cannot be sustained. The good news
~eepers is that most corals can adapt to a
wide range of light intensities. However, the healthiest and fastest-growing corals are found in shallow waters with intense light. This means that in choosing a lighting system for a reef tank, the most important consideration is intensity.
COLOR TEMPERATURE
As light passes through water, longer-wavelength light toward the orange and red end of the visible spectrum is absorbed more quickly than shorter-wavelength light toward the blue and green parts of the spectrum. Consequently, the majority of light that reaches the lower depths of a coral reef is blue. This phenomenon has been used to argue in favor of tank lighting that is primarily blue. There are, however, a number of problems with this argument, both scientific as well as practical.
First, corals can be found along a wide gradient of depth and therefore along a wide range of color temperatures. The deepest corals do survive in water that is virtually monochromatically blue, but corals at these depths are a deep chocolate brown, slow-growing, and not particularly attractive or colorful. The most striking corals - the ones that
command the highest prices in the hobby - are
found in shallow waters perhaps no more than 3 to 5 feet deep. The light at this depth is little different from natural sunlight and is a low color temperature by hobby standards. If the goal is to recreate light similar to that found in shallow natural reefs, one should use some of the lowest-wavelength Kelvin lights sold in the hobby today.
A second related argument that high-color-temperature supporters make is based on academic research first conducted several decades ago. Studies begun in the 1970s examined the absorption of light by zooxanthellae and corals, and found that zooxanthellae absorb some wavelengths of light more than others. An early study determined a broad absorption peak between 400 and 550
nanometers (nm) , and a second smaller peak between 650 and 700 nm. Believers point to the fact that high-wavelength Kelvin bulbs generally have a large emission line near the short-wavelength absorption peak, proving their superiority. The problem with this argument is that more than 10 years ago, I showed that lower-wavelength Kelvin bulbs produce more light in the blue spectrum than higher-spectrum Kelvin lights. All the work completed since the initial study (e.g., Sanjay Joshi's "Spectral Analysis of 175-Watt Metal Halide Lamps," Advanced Aquarist, November 2005) confirms this. Furthermore, the zooxanthellae absorption curves are quite broad. In truth, most full-spectrum light bulbs sold in the hobby today produce a great deal of light in the area of both peaks.
There are also more practical reasons to favor low-Kelvin bulbs over their higher-Kelvin equivalents: intensity and longevity. Metal halide bulbs are so named because their light is created by the ionization of metal halides within a glass envelope or blub. The broad-spectrum bulbs used by the hobby are created by combining exotic-sounding
metal halides, such as dysprosium, scandium, holmium, thallium and indium. Over time, these halides are. depleted and collect on the bulb's glass envelope. This is why the glass envelope darkens over time, reducing the intensity of the bulb. A "cocktail" of several different halides generates a
broad spectrum, but more importantly, creates light that degrades more slowly. The spectrum will
shift slightly, but a broad-spectrum bulb T".l tinue to generate large amounts of light ~ _ A higher-Kelvin bulb contains a more liIIrir.e::: halides that degrade more rapidly.
The very blue 10,000 to 20,000K b~ iiI . ular in the hobby have a more specialize,:; halides that creates a more monochror::a:r Because of the mix of halides, these b~ orate more quickly. This means that ~ ing under these bulbs are constantly ~ adapt to declining light levels. Some CC:-~ adapt quickly, but other corals may noc. ~ solution for the hobbyist is to replace the ~ few months.
METAL HALIDE CHOICES
The most important consideration for lighting for a reef tank is intensity. So. :::2 is to create a healthy stony coral reef trL L ~ byist should choose the brightest ligh~ . or her budget permits. For tanks 90 ga:...:ns smaller, one or two 175-watt bulbs W':: T';tt. tanks larger than 90 gallons, multipre :: -:= . or fewer 400-watt bulbs should be used. c~ the most important lamp parameter:s choose the bulb with the highest phoLU:>} ~ active radiation (PAR), a measure of ligffi
Despite the availability of more thaI: 1...= new bulbs in the past decade, those ~ use a decade ago are still some of the ::-..:s:: effective. Although these low-wavele~...:..
bulbs may not generate the most attractive color in an aging reef tank, their effectiveness more than compensates. If one wants the tank to look more blue, one solution is to add actinic fluorescent tubes. This is a simple and inexpensive answer. If this isn't practical, switching to 10,000K bulbs may provide more blue, but intensity will suffer.
The labeling of bulb color temperatures is primarily a marketing effort rather than a true indication of the color of light generated. Some bulbs labeled as 10,000K are bluer than some 20,000K bulbs, so the only reliable way to judge a bulb's color is to see it. There is no need to analyze the spectral charts of the bulbs under consideration, because bulbs that generate similar-colored light will have similar spectral charts. PAR is all we need to consider in choosing between similar bulbs.
REFLECTORS AND OTHER ISSUES
The preoccupation with spectral quality, fueled by the flood of light bulb data, has distracted the hobby from more important considerations when it comes to lighting a reef tank. Reflectors can make a greater difference than bulb selection in how much light reaches into the tank. Both the materials used, as well as the shape and design of a reflector, are very important in maximizing the value of a hobbyist's lighting investment. One advantage of an assembled lighting system rather than a homemade system is there's a greater likelihood that all the parts of the system work well together.
Lighting maintenance is also critically important. Salt accumulation on bulbs, reflectors and shields can significantly degrade lighting systems. Hobbyists who allow salt spray to accumulate on bulbs and reflectors can lose a high proportion of the light generated. With poor maintenance, a 400watt system can produce little more than a clean
175-watt system. Lighting is expensive enough without wasting light and electricity. Make sure that cleaning all lighting components is a regular part of maintenance.
THE NEXT STEP
The hobby enjoyed rapid progress in lighting during the 1990s, but since then there have been limited gains. Today, we can keep most corals healthy and growing, but that was true a decade ago. And issues that confounded hobbyists a decade ago continue to do so. Brightly pigmented corals are highly prized and command top dollar in the trade. Unfortunately, too often they begin to lose their bright colors once added to a reef tank.
We can now create light intensities equal to those found on natural reefs, so intensity does not seem to be the issue. We can create the same color temperature of light found in shallow reefs where highly pigmented corals are found, so this does not seem to be the issue, either.
The one component of natural light we do not recreate very well is ultraviolet (UV) light. Sea water absorbs UV light fairly quickly, but UV light does penetrate the first 10 feet or so of water, where the most colorful corals are found. Research has shown that the brightest pigments are used to shield corals from potentially damaging UV light, so we may need to supply a reef tank with some UV light to make the pigments as bright as possible.
Excessive UV light can be potentially dangerous to both the hobbyist and reef tank inhabitants, so this is one area that requires caution. Broken metal halide shields or outer envelopes can emit dangerous levels of UV radiation. However, judicious use of some UV may be the missing component to re-creating natural sunlight in the reef tanks of the future.
