Tropical Aquarium - Should incandescent or fluorescent light be used?

Some reflectors are fitted with sockets for a fluorescent tube instead of incandescent bulbs. There is a good deal of controversy concerning the relative merits of the two systems. Experiments conducted by Dr. C. W. Coates at the New York Aquarium indicated that a combination of both incandescent and fluorescent lighting gives the most satisfactory results. His experiments also showed that light, in order to be satisfactory, must be directed from above. Light from the side has a greatly decreased value.

It is impractical for the average hobbyist with a small or medium aquarium to use both types of light, however. Properly used, either will give a satisfactory growth to the average aquarium plant, although it may not necessarily give maximum growth.

The initial outlay for a fluorescent fixture is slightly higher than that for an incandescent. This is offset by the fact that a fluorescent bulb consumes much less current. Also, the higher cost of a replacement tube for a fluorescent is balanced by its longer life. In addition, fluorescent fixtures give a stronger, more even light, and they do not heat up the aquarium. This is particularly important during the summer, when preventing any increase in the already high water temperature and yet supplying enough light for the plants can be a problem. When using a fluorescent, the red end of the spectrum should be favored for color because it is the most beneficial. White, cold white, and daylight bulbs are not so satisfactory as warm tints, warm tones, or deluxe warm whites.

As with an incandescent, the time for the required for the fluorescent to obtain results is extremely variable. In general it should burn two to three times as long as an incandescent reflector under comparable circumstances.

For tanks of 20 to 30 gallons in capacity, the standard reflector holds a 20-watt bulb. It is frequently necessary to burn a bulb of this size twenty-four hours a day in order to achieve satisfactory plant growth. For smaller tanks, sixteen to twenty hours of light a day is usually necessary. If it is inconvenient to turn the light on and off at the time necessary to provide the proper illumination, it is perfectly satisfactory to burn the light twelve hours one day and twenty four hours on alternate days.

One of the most satisfactory tanks I had experience with was a 27-gallon aquarium owned by a businessman. It measured 36 inches long by 12 inches wide by 14 inches high, and was equipped with a 20-watt warm-white fluorescent fixture which burned continually. The plant and fish growth in that tank was phenomenal. Ambulia, Amazon Sword Plants, Hygrophila, and Cryptocoryne of different species grew in profusion. Magnificent fish luxuriated among the dense growth. No attention was given to the tank other than feeding and replacing water lost through evaporation. Every month a pet shop owner was called in to siphon the bottom clean, and to remove a pailful of excess plant growth.