Light spectrum and intensity for aquariums (continued)
Saltwater reef aquariums
The type of light provided for a saltwater reef aquarium is very important due to the fact that the corals and invertebrates that live in the system rely on light for a major portion of their nutritional needs. The intensity of light that corals and invertebrates require varies dramatically. This is due in part to the varying landscape of the reef and the adaptations that many corals have made to survive in low light conditions. If the correct spectrum and intensity of light is not provided for these organisms, their survival rate will be poor.
Most of the corals that are collected for the hobby come from areas surrounding the reef at a depth of 15 to 65 feet. In the wild, they receive light that is primarily blue in color with a high Kelvin rating.
As with any aquarium, when considering different types of lighting, both the initial and operating costs, intensity and spectrum of the lighting, and the heat that is associated with the unit must be considered. Due to the high costs involved with lighting systems for reef aquariums, they tend to be one of the major expenses of the installation. Not only is the initial expense high, but also the amount of electricity needed to run these systems. Also, depending on the type of lighting, the regular bulb changes can be very costly and will add to the operating costs.
A general rule, to correctly light a reef aquarium that is 24" deep or less, provide between 4 to 6 watts of light per gallon. Of course there are exceptions to this rule. Aquariums that are shallow, 16" or less, do not require the intensities of taller aquariums. Also, a reef aquarium could be set up to house both corals and invertebrates that require low levels of light, as well as non photosynthetic invertebrates. In no case would I suggest going below 2 watts per gallon when photosynthetic invertebrates are to be kept.
Because of the conditions in nature, all invertebrates have adapted to use light that is from the blue side of the spectrum. There are bulbs available for most lighting systems that focus on this wavelength. For example, fluorescent systems offer bulbs that are strictly blue in color. These bulbs are called actinic. Although most corals and invertebrates can be successfully grown under blue light, this type of setup can be unpleasing to the eye. So, most systems will employ actinic bulbs for the health of the system in conjunction with another light source that is mostly white in color for aesthetics. A general rule for reef aquariums is to provide approximately 1/2 of the light from actinic bulbs and 1/2 from bulbs producing white light in the range of 8000 to 12000 K. This mixture of lighting provides the invertebrates with the spectrum that is necessary for growth, and produces the spectrum that is necessary for accurate color rendition within the aquarium.
The heat that is associated with the lighting systems designed for reef aquariums is substantial and needs to be addressed prior to the installation. Typically, wattage is translated into heat no matter what type of lighting it is. But, there are two types of heat involved. The first type of heat is in the air surrounding the bulb, which can be removed with the use of fans. The second type of heat is the radiant heat that is produced by the lighting system. This heat, unfortunately, is absorbed by the aquarium water and cannot be removed with the use of fans. Because of this radiant heat that is produced by all of the more powerful lighting systems, it may be necessary to consider the price of a water chiller when determining the cost of the system.
As with planted aquariums, base your decisions on the type of corals and invertebrates that you wish to incorporate into the system by the amount of light that you can provide for them.
Conclusion
When designing an aquarium, it is important to include the necessary lighting components into the budget that will provide the inhabitants with the spectrum and intensity of light that they receive in nature. By duplicating these conditions, we greatly increase both the survival and growth rate of these organisms, while portraying that ecosystem in a more realistic manner.
