Garuf said:
Actinic lighting is useless over a planted tank, it's used to promote coral growth.
This is completely untrue. Any light in the visible spectrum is useful to plants. It turns out that as light enters water, different wavelengths with different "energies" will penetrate to varying depths. Red light (630-780 nanometers) penetrates only to about 15 meters, while blue light (420-490 nanometers) can penetrate to as deep as about 250 meters. This is why the ocean appears blue.
Actinic bulbs peak somewhere in the 420 nm range.
Any plant can use blue light, not just algae. In general, red light stimulates photosynthetic carbon fixation which is incorporated into glucose, while adding blue light causes a metabolic shift so that the fixed carbon is used to synthesize organic acids, amino acids and proteins. As long as the intensity (i.e Photon Flux Density) of the light is sufficient to fix carbon from ambient CO2 the wavelength within the spectrum is irrelevant.
Garuf said:
Corals are not algae. They are animals who have incorporated and thus share a symbiotic relationship with zooxanthellae algae. Since most corals are found in shallow waters below the red light penetration zone it is assumed that this blue wavelength is optimal for the zooxanthellae algae. This does not automatically mean that only algae can use blue light.
The best light therefore has nothing to do with what color or Kelvin rating the bulb has. Kelvin ratings are totally and completely meaningless. In fact the bulbs these days are not even accurately rated with the correct Kelvin rating. It's actually a joke. Best light has only to do with what our eyes perceive as an aesthetic. Therefore if firstman finds his current combination adequate aesthetically then there is no reason at all to spend more money getting different bulbs. Having said that however, note that the human eye is not very sensitive to blue light and they may make the tank appear dim and colors of the plants to be slightly off.
Cheers,
