Revisited: The Varied Lighting Options for an Aquarium

There has never been a more debated topic concerning reef aquariums than lighting. Since the popularity of reef aquariums began to grow in the early 1990's, there have been many advances in lighting for the aquarium. This article will focus on the different types of lighting available on the market and hopefully provide insight as to which one is the right choice for you. There are some basic terms that are commonly used in describing types of light bulbs/fixtures and spectrum. Unfortunately, there is no "standard" by which to govern many of the manufacturer's claims, which only add to the confusion.

Color Temperature

Since many of the invertebrates we are trying to keep are photosynthetic, containing zooxanthellae within their tissues, many of the bulbs target natural sunlight with emphasis on spectral peaks in the blue range (420-490 nanometers). Blue light has been shown to penetrate seawater to much deeper depths and is readily absorbed by corals. When it comes to identifying a bulb's spectral range, the Kelvin rating is a very important factor. Daylight, or sunlight, typically falls into the 5500-6500 Kelvin (K) range. Most bulbs in this range "appear" to have more yellow and are not the most aesthetically pleasing, although they are the closest to natural sunlight. The home aquarium is a display and most aquarists want both healthy corals and a visually pleasing exhibit. This is the main reason 10000-20000 K bulbs have become so popular. It should be noted that manufacturer's claims on the Kelvin rating vary highly and there is much variation between one bulb and the next, even with the same Kelvin rating. Some aquarists use lower Kelvin bulbs, such as 6500 K metal halides, while using higher Kelvin fluorescent lights to supplement the blue wavelengths (20000 K or 20K). These are commonly referred to as actinic bulbs, a name coined by the German lighting company Osram/Sylvania. While most corals for the aquarium trade adapt to many different spectral ranges, care should be taken to understand what the light requirements are for the desired species.

Light Intensity

Intensity, Photosynthetically Active Radiation (PAR), and Lux are all terms used in discussing the amount of light being given off by a light source. When selecting a light for the home aquarium, these terms are rarely used in marketing products. Besides the Kelvin rating, as discussed above, the wattage of the bulb is the next consideration. Generally speaking, the higher the wattage, the greater the output. Typically, a range of 4-8 watts per gallon is recommended for photosynthetic corals. There are a number of factors that affect the amount of light needed for the aquarium. The depth of the tank, the distance of the light source from the aquarium surface and water clarity are just a few variables that can increase or reduce the amount of light being transmitted into the tank. In addition, soft corals and large polyp stony corals typically do not need as much light as most small polyp stony corals and therefore species selection plays a key factor in how much light is needed. Once the type of aquarium (depth, species, etc) is chosen, the next decision is which type of lighting is best.

The Different Types of Lighting

There are a number of different types of lights on the market today. The most common is fluorescent lighting. Previously, popular fluorescent lighting was a "T12" bulb that measured approximately 1 inch in diameter and was available in a variety of different lengths. The four-foot bulb carries a rating of only 40 watts. This creates problems when trying to reach some of the suggested light ranges that are needed for photosynthetic corals. Typically, there is not enough space above the tank to place the required amount of T12 bulbs in order to meet the minimum lighting requirements. Due to these limitations, a very high output (VHO) T12 was created. These lamps generate much heat, are not energy efficient and have a short life (4-6 months). Then came the compact fluorescent. This is a high output (HO) bulb that creates a more intense output. Compact fluorescents also use less energy and bulb life is almost twice that of a standard fluorescent. The newest form of fluorescent lighting is called T5, which measures 5/8 in diameter. This type of bulb is quickly gaining popularity due to its high output, even smaller space requirement, low energy demand and bulb life. Using less energy while creating less heat (reducing the need for a chiller, etc) is something we all strive for in maintaining our aquariums. Another common type of lighting is metal halide/HQI. For many years, this was considered the best type of lighting for small polyp stony corals and certain species of clams. The point source effect of a single bulb mounted over an aquarium creates "glitter lines", which many aquarists find visually appealing. There is research that shows these lines actually concentrate light, almost magnifying the intensity. Metal halides come in a double-ended (DE) and single-ended (SE) bulb configuration. Metal halides are preferred on aquariums over 24 inches deep, due to their ability to penetrate deeper than fluorescents. The latest technology is light-emitting diode (LED) lighting. This light uses a series of small diodes to emit light into the aquarium. Early tests show that they are energy efficient (40% less consumption than metal halide), reduce heat transfer and have adjustable color temperature (Kelvin) abilities. LED also has a 50,000-hour life, thereby lasting over 11 years on a 12-hour daily photoperiod. One of the major disadvantages of this type of system is cost, although the manufacturer claims this can be recouped quickly due to lower operating costs. It is important to note that the type of reflector used with any system plays a vital role in how the light is directed into the aquarium, thereby maximizing the efficiency of the bulb.

Lighting has come a long way in the past 10-15 years and it will be interesting to see where the next advances will come. One thing is for sure, the hobbyist has more great options to choose from than ever before. As we continue to learn more about what corals need and how they control pigmentation within their tissues, lighting technology will be not be far behind in offering a system for the hobbyist to try on their aquarium.

The advent of electronic ballasts has added to the variety of options available to today's hobbyists. Electronic ballasts are standard on all fluorescent lamps, but the choice is yours when choosing metal halides, since there are many lamps/fixtures available with magnetic or electronic versions. Electronic ballasts are lightweight, produce less heat and can be easily mounted inside the fixture. Most lighting systems are available as a retrofit to an existing system or as a complete fixture with integrated cooling fans and timers.