03-24-2010, 08:02 PM
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That is one reason I do not like the "aquarium" or "plant" tubes; they are high in blue and red and the aquarium takes on a distinctly purplish hue. It is interesting that such tubes are also much weaker in light intensity. Any tube labelled "Aqua-Glo", "Flora-Glo", "Grolux" or designated as aquarium or plant light will produce purplish light.
It is true that plants use specifically blue and red light; but adding green/yellow to the combination results in light that looks more natural and provides a natural colour rendition of fish and plants. Tubes labelled as full spectrum, daylight, natural light, enhanced daylight, ultra daylight, etc., will usually be fine if they have a kelvin rating from 5500-6700K. There is also warm white, slightly more red or "warm" tones, and cool white which is more blue for a "cooler" tone; the 5500K will be on the "warm" side, the 6700K will be closer to the "cool" side. With one tube over a tank aim for one that is balanced or full spectrum; with two tubes you can mix full spectrum and cool white.
Unfortunately almost all fixtures come with one of these "special" tubes; I bought two All Glass fixtures last year to replace aging ones, and I sent these tubes straight to the recycling and used my own.