Reef Aquarium Lighting

Why Lighting is so important ?

Lighting is one of the most important aspects of a successful reef aquarium. It is also one of the most expensive components to purchase and maintain. Reef Aquarium lighting is designed to replicate the light qualities found on a natural coral reef. Before purchasing a lighting system, it is important to understand why corals require light in order to flourish.

Many corals and invertebrates rely on light for a major portion of their nutrition. These corals, anemones and other cnidaria share a symbiotic relationship with a type of algae called zooxanthallae. It is the zooxanthellae that require proper light. These zooxanthallae live within the tissues of their hosts.  They contain Chlorophyl pigments which "harvest" light and use it for the process of photosynthesis. These products of photsynthesis (carbohydrates and oxygen.), can then be utilised by the host organism as a source of energy. The host then provides a "safe" place to live as well as the nutrients (nitrogen and phosphorus) that the zooxanthellae require.

There are many corals that do not contain zooxanthellae, such as "Sun Corals" (Tubastrea species), "Carnation Corals" (Dendronephthya species) and others. Generally, these corals are difficult to keep and it is best to first get experience with corals containing zooxanthellae.

Millions of zooxanthellae can live within the tissues of a single coral colony. The brown coloration of many corals is due to the zooxanthellae. 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. If the coral becomes stressed (too much light, water too hot or cold, too much ultraviolet radiation, etc.), it will often expel zooxanthellae. The coral then is said to be "bleached" and will probably die. It is therefore, crucially important to the health of the coral to maintain sufficient lighting and keep the zooxanthellae healthy.

Many corals can acclimate to different lighting levels over a long period of time. This occurs naturally in the wild due to seasonal changes. Corals are far less adaptive to rapid changes in lighting.  Most corals have light intensities at which they grow best. This is important to know when selecting bulbs and determining at what depth a certain coral should be placed.  Remember not to place new corals in a high light area of your tank. This may lead to light shock or bleaching of the zooxanthellae. Place new corals deeper in the tank and provide some shading. Once acclimated, (generally about 2 weeks), raise them slowly to the desired level.

Photoperiod

Most corals will require a photoperiod of around 12 hours. Many reef keepers will place their blue lights on a seperate timer to the other lighting regime . This allows the blue tubes to turn on around an hour before, and turn off around an hour after the other lighting. . It is thought that this simulates the twilight experienced in wild reefs at dawn and dusk.

Measuring Light Intensity
Aquarium lighting is rated in terms of wattage (W) and kelvins (K).
Wattage describes how much power a particular lamp will use. This tells you how much electricity the lamp will consume and gives a rough indication of how much light a particular lamp will output. The higher the wattage the greater the amount of light and the deeper it will penetrate.

Kelvin is a scale that has been developed to describe the color of light. As a general rule, reef aquarium lighting should not fall below the 5500K rating which is close to the Kelvin rating of natural sunlight at noon. The lower the K rating, the greater the color of the light will lean toward the red side of the spectrum. The higher the Kelvin rating, the greater the color of the light leans toward the blue end of the spectrum and is said to have a higher color temperature. Reef aquarium lighting generally ranges from 10,000K to 20,000K.

In the natural reef environment, water depth greatly determines light intensity.  As light enters the water and passes through the first 15 feet of water, the red and orange wavelengths are absorbed by the water, increasing the K rating of the light, and giving the light a bluer appearance. Most of the corals that are collected for the hobby come from areas surrounding the reef at a depth of 15 to 65 feet where they receive light that is primarily blue in color with a high Kelvin rating. This is why it is essential that a reef aquarium is supplied with enough blue light.

Lighting options

Metal Halide

Metal Halide lighting is a very popular lighting option. Metal Halide lamps use various earth metals to allow the lamp to burn in certain colours. They produce high light output relative to their size making them a compact and powerful light source. Metal Halide lamps require ballasts to help them regulate the arc current flow and some require an ignitor to fire.

Another advantage of the MH bulb is that it is a point light source. This means the light comes from a single point, which causes a ripple effect in the water, very similar to what is observed in nature. The most commonly used metal halide lighting systems are 150W, 250, and 400W with bulbs of 10000K, 14000K and 20000K.

Most people suggest changing the bulb ever 12 to 18 months. A disadvantage of metal halides is that they tend to generate alot of heat. As a result, it may be necessary to install a fan or a chiller to control excesive temperatures, particularly in the summer months.

A general rule is to install one metal halide lamp for every 2ft of tank length. For a tanks below 2ft high,you can use 150W metal halide. For a tank that is 2ft high, go for 250W metal halide. For a tank that is 75cm high, go for 400W metal halide. These guidelines will allow sufficient light penetration to all available areas of the tank enabling most corals to be kept in a reef aquarium.. Remember to place corals according to their lighting requirements with corals which require lower light levels placed lower in the tank.
 
Fluorescent Lighting

Fluorescent lighting is probably the most popular form of aquarium lighting. Fluorescent bulbs come in various intensities. Normal Output (NO), High Output (HO)  Very High Output (VHO) and Power Compact Bulbs. Fluorescent lamps are sold by length rather than wattage and come in standard sizes of 1, 2, 3 and 4 foot, the longer the tube the higher the wattage. The lamps are sized according to the length of standard aquarium lengths e.g. a 4 foot aquarium will require a 4 foot fluorescent lamp. As well as different lengths, fluorescent lamps come in different thicknesses which determine the crossectional diameter of the lamp. The most common of these are T5, T8 and T12 lamps.

Normal Output (NO) fluorescent bulbs are sold with most light hoods by your local fish store/local pet store. These are fine for fish only aquariums. For Mini-Reef tanks they do not provide enough light to keep most corals alive.

High Output (HO) T5 have a higher wattage compared to similar sized tubes and therefore a greater light output for the same tube length. HO bulbs require a HO ballast.

The development of electronic ballasts for Very High Output (VHO) fluorescent lighting, has allowed enthusiasts to design high wattage systems in small spaces. VHO fluorescent lighting will give you all the spectrum necessary for corals. They are a practical, less expensive alternative to metal halide lighting while keeping the adequate spectrum for your coral lighting, and they run cooler. The expensive part of a VHO setup is the ballast required to operate the bulbs.

Power Compact bulbs are a variation of the VHO florescent bulbs. The variety of bulbs is very low compared to VHO or NO bulbs.

What is the Correct Lighting System?

It is useful to remember that there is no single correct lighting system or regime, but many variations which may bring you success. There are a wide variety of products on the market and many will claim to be "the best". Most of them are very good and will maintain very healthy corals. Before purchasing an expensive lighting system, consider the livestock you wish to maintain in your aquarium. Do some research and learn about the lighting requirements for each  individual species you plan on keeping.

It is worth spending time to research before purchasing. Many of us have been misled or confused by salesmen in stores and as a result taken home items either totally inadequate or unnecessary. Knowledge will give you the confidence to purchase a system that will give you many years of pleasure, and a tank full of attractive healthy corals.