Spectral Characteristics

What about the quality of the light, its spectral characteristics, or, if you prefer, its "color"? Sunlight is composed of many wavelengths (colors) oflight. To meet the needs of photosynthesis and to create a natural appearing aquarium, a light source that duplicates the spectrum of sunlight as closely as possible is desirable. There is a relatively simple way to compare the spectral output of various light sources to that of sunlight. This is called the Kelvin temperature scale. Noonday sun under clear skies has a rating of 5,500 degrees Kelvin (K). This is a bluish white light.

Lower Kelvin temperature ratings will be progressively more red in color, while higher temperatures are progressively more blue. Thus, the nearer the Kelvin temperature of an artificial light source is to 5,500 degrees K, the more closely this source mimics the color of sunlight. Kelvin tempera ture data on virtually any lamp can be obtained by checking the specification sheet for that lamp type, available from the lamp's manufacturer. The Phillips Ultralume fluorescent lamp used in the example earlier has a rating of 5,000 degrees K. The aquarist should use lamps that have a high Kelvin-degree rating, at or above 5,000 degrees K, if possible. (Bulbs intended for other uses are often inappropriate:

horticultural lighting is typically in the 4,000 to 4,500 K

range — "redder" or "warmer" than the ideal for reef tanks.)

It is possible to combine different types of fluorescent lamps to achieve both high intensity and a suitable spectral rating. High output (HO) and very high output (VHO) fluorescent lamps are very bright and come in many suitable types. These lamps require special ballasts and the bulbs will need to be changed more frequently (about every 6 months) than standard fluorescent lamps. Standard lamps should be changed every 9 to 12 months, owing to shifts in the spectral output of the lamps during prolonged use. The point is that many fluorescent lamps and combinations of lamps will work as aquarium light sources. The list of available lamp types is seemingly endless. Only by experimentation can one determine if a particular combination is going to be satisfactory for the organisms in any given aquarium, taking into account both the needs of the organisms and the appearance of the tank. Different types of lamps also give different biological results. For example, I find that macro algae seem to grow better under illumination that is higher than 5,50(: degrees K. Various genera, including Caulerpa (several species), Penicillus, Halimeda, Udotea, Cymopolia, Valonia, Dictyosphaerium, Gracillaria, Hypnea, and several others, grew in my aquariums under fluorescent lighting. All of these species, however, as well as corals and anemones, do as well or better under metal halide lighting.

As many people may be aware from extensive discussion in the aquarium literature, sunlight s colors are progressively filtered out by the water as one descends deeper into the

112 Natural Reef Aquariums

5000 Reef Lighting

#1. Expert aquarist Michael Palettas large reef system under four different lighting schemes, starting with 6,500-degree K metal halides

Blue Soft Coral

#2. The same section of Paletta's stony coral aquarium with all-actinic fluorescent lighting, clearly displaying a distinctive blue cast.

ocean. Many stony and soft corals grow at depths where all of the light is in blue wavelengths. (The longer red wavelengths are absorbed near the surface, while the shorter blue wavelengths penetrate most deeply.) Lighting systems with lamps rich in blue wavelengths are often included for the benefit of these specimens, although the effect, while it is a realistic depiction of the appearance of the reef at these depths, may appear unnatural or eerie to some observers. Also, the beautiful colors of some deep-water species are only apparent when they are exposed to full-spectrum illumination. This is why many hobbyists, as well as public aquariums, use white rather than blue light for the majority of their displays.

Shallow-water species, of course, should always be illuminated with white light. Red wavelengths are absorbed by green pigments, and specimens with bright green pigmentation probably came from shallow waters where red wavelengths penetrate. Golden-yellow pigments, found in zooxan-thellae, absorb blue light. These pigments are found in all photosynthetic invertebrates, suggesting that providing blue light is beneficial. Many species produce pigments that fluoresce in blue light, a sure sign that the light is interacting with the pigment but not necessarily an indication of any biological effect of the light. (The vibrant fluorescent greens and blues seen under actinic-blue or so-called 03 actinic lights account for their inclusion in the mix of bulbs over many reef setups.) Ultraviolet (UV) protective pink or purple pigments are produced by many species of cnidarians exposed to high levels of UV in shallow, brightly illuminated locations. Such specimens may lose their colorful pigments if transferred to another light regime.

Chapter Four 113

The COMPLETE guide to Aquariums

The COMPLETE guide to Aquariums

The word aquarium originates from the ancient Latin language, aqua meaning water and the suffix rium meaning place or building. Aquariums are beautiful and look good anywhere! Home aquariums are becoming more and more popular, it is a hobby that many people are flocking too and fish shops are on the rise. Fish are generally easy to keep although do they need quite a bit of attention. Puppies and kittens were the typical pet but now fish are becoming more and more frequent in house holds. In recent years fish shops have noticed a great increase in the rise of people wanting to purchase aquariums and fish, the boom has been great for local shops as the fish industry hasnt been such a great industry before now.

Get My Free Ebook

Post a comment