Reef Lighting By C Marlowe

c marlowe

When it comes to lighting a reef tank, it really depends on what you plan to keep in it, and how much light is required for the creatures you would like to have. First lets look at why corals even need light since they are not plants, but animals instead. Alot of people don't realize that the light loving corals we keep are infact two seperate lifeforms that live together, one being symbiotic algae and the other being the coral animal. Many of the corals we buy contain algae in their tissue. These collective dinoflagellates (algae type) in the corals tissue are called zooxanthellae. The zooxanthellae living within corals is why corals need light (corals themselves need no light). The zooxanthellae that uses the coral as a host is actually what uses the light we provide for photosynthesis, and since zooxanthellae helps the coral it is more than happy to let them invade and live within its tissue.
The coral and the zooxanthellae both benefit from this symbiotic relationship by helping each other. The coral gives the algae a safe place to live within its tissue and feeds it with its wastes in the form of carbon dioxide and nitrogen, and while feeding on these wastes the algae then returns the favor by feeding the coral with the production of amino acids and such.
Zooxanthellae can be expelled if the coral isn't treated right, becomes stressed, or if the zooxanthellae is threatening the corals life by not maintaining the correct balance between the two. Many things can cause this, and when a coral expells its zooxanthellae, it is refered to as "bleaching"
. Improper lighting is one of the many things that can cause bleaching. There are many different zooxanthellaes, and when a coral does bleach, it is very possible if death doesn't occur that the coral will except a zooxanthellae that works better with it's current conditions.
Zooxanthellae has what is called it's "compensation point"
, and this is the minimal amount of light required for it produce enough oxygen through photosynthesis for it to live. Leaving the lights on for longer periods will not help either because the zooxanthellae will not produce enough constant oxygen throughout the day, and it will not use enough of the corals waste to be of any use. The "saturation point"
is the maximum light level and exceding this point will not increase photosynthesis, so there is little point to going above this level. "Photoinhibition"
is the point where too much light will cause photosynthesis to shut down.
The possible lights....
in my opinion are mostly for fish only tanks, but if you have room for six or more, they can be used on a reef tank. They come rated at 15,20 and 40 watts, and are the cheapest for the folks on a budget. These lights are a poor choice for most reef tanks, although they may be used with the lowest light requiring creatures.
will need a special ballast (I personally use an icecap, but others are available), and VHO bulbs are more costly than regular fluorescent usually. In my opinion they should be changed around once a year at the very least. VHO lights come in 75, 95, 110, 140, and 165 watts. Like the regular fluorescents, they come in long tube styles.
are "U" shaped fluorescent lights that come in 55 and 96 watts. Change these atleast once per year also. Just like the other fluorescents, they will work in the right conditions for a beautiful tank.
provide intense light that is more crisp looking than flos, produce alot more heat, and should in my opinion be atleast 7 inches off the water. Cooling these lights with fans can sometimes dim the bulbs, but steps need to be taken if the water temperature rises too much. Unlike tube lighting, halides can give you a nice ripple effect in the tank that is much more natural because the light comes from a point source. They are a good choice for deeper tanks because they will punch down into the water further. The cost is higher and the heat is greater, but most folks aspire to have them for their advantages. MERCURY VAPOR LIGHTS are not very commonly used, and they come in 80 and 125 watts. They can lose their color spectrum in as little as 3 months, and usually peak in the green/yellow/orange areas of the spectrum, so blue support is probably a good idea although some brands do have MVs more suited to the hobby. They also do have the advantage of the ripple that only pendant style light can produce.
Lights to avoid......... <img src="graemlins//eek.gif" border="0" alt="[eek]" />
need to have a special ballast, and they give off very yellow light.
are better for outdoor lighting, and they produce alot of heat and yellow color.
Basically any of the above lights will work depending on your personal set up and the creatures you plan to keep. As far as what is the most important aspect of lighting....that is still argued throughout the web and on all the boards including this one, so I will not offer my opinions here. The majority of the corals we keep come from a range of 33-66 feet of depth from my readings, and this is why blue light is quite important. Although the sun produces a full spectrum of colors at around 5500-6500 kelvin, the colors do not penetrate the water to the same depths and basically this is why we don't just simply try to duplicate the suns Kelvin rating. The bluer end of the spectrum penetrates water much better than the red or yellow end, so the water looks bluer at greater depths since that's the end of the spectrum that reaches deeper. Although blue light is very important, the higher Kelvin the bulb, the less intensity it will have, so a more powerful bulb is needed to achieve the same light energy from an actinic as opposed to a full spectrum bulb. A combination of higher and lower Kelvin bulbs is a commonly used effective way to go for looks and effectiveness. The zooxanthellae algae living in symbiosis with the corals has adapted to their natural lighting, and in my opinion it is important to try to recreate their natural environment as best we can in our home tanks and bring out their natural color and health.
Remember that if you do not use reflectors with your lights, that you will be losing 1/3-1/2 of the bulbs capacity!!!
The most important thing about giving corals the correct lighting is to research each and every coral you buy before you buy it, and to understand what type of lighting they require. There are many beautiful corals that do not have zooxanthellae, but these corals are generally harder to keep, and require that their feeding needs are met.
Here's a few important things to consider in reef lighting, and a few terms for your knowledge even if they are never used by you, as I only really consider a few, and I can't even test most.
is a measurement of light energy, and this is called photon flux, and it is more simply measured in terms of irradiance than by microEinsteins.
is photosynthetically active radiation, basically the light between 400 and 700 nm that could possibly be used by the zooxanthellae.PUR is photosynthetically usable radiation, and it is basically light that can be used depending on coral color and water conditions.PSR is photosynthetically stored radiation, and it is the light that is used in photosynthesis, and it will be close to PUR.
are a measurement of irradiance.
is a measure of light intensity.
when applied to lighting is the color temperature. Basically the color the light gives off.
are the power used by the ballast to run the lights, and are not a very good indicator of output, although a simple way to describe a light that is used very often.
is made up of all the different wavelength that we see as color. red,orange,yellow,green,blue,indigo, that order. the spectrum is measured by looking at the lights peaks in certain wavelengths.
is measured in lumens and is the amount of light energy that over a given time strikes on a given area.
color rendition
cannot really be measured because it has more to do with the appearance to each persons human eye, so it measures how accurate a colored object appears under a certain light, basically does the object show its true color?
ripple effect
this is a very sought after effect caused by point source lights going through a disturbed water surface. The light is magnified and distorted and the natural effect you would see under water is achieved.
is the algae that lives within the corals tissue in a symbiotic relationship.
symbiotic relationship
this term has been argued a few times, but I will define it simply as being a relationship where both parties benefit from each other. Corals and the light loving zooxanthellae living in their tissue is an excellent example.
I'll add more later when I get a chance and think of them. ;)