This experiment’s results suggest information potentially valuable for hobbyists - that rates of photosynthesis were essentially the same under these two distinctly different light sources. Other than aesthetic value, there appears to be no advantage, photosynthetically speaking, in using high Kelvin lamps.
The implication of these results should be of interest to hobbyists; it suggests that lamp selection (with due regard to lamp intensity) may be based on appeal, whether that is price or the "look" it gives to a tank, without fear of hindering photosynthesis. Economy-minded hobbyists and coral farmers may find this especially useful. It appears that light intensity and relatively simple light measurements alone adequately judge lamp efficiencies within the context of zooxanthellae photosynthesis. This should not be construed to mean that all light sources are adequate for reef aquaria use.
The spectral signatures obtained with the spectrometer demonstrate that these two metal halide lamps are full spectrum (though the 12,000° K lamp output is skewed towards the blue portion of the spectrum) and most resembles the "white light" category defined by Kinzie et al. (1984). Results garnered with the PAM meter suggest these two lamps are more or less equally efficient in the promotion of photosynthesis when PPFD values are the same.
It is inappropriate to claim that there are no major differences among the plethora of lamps available and their abilities to promote photosynthesis. Certainly the depreciation of overall lamp light output (PPFD) should be considered and readers are encouraged to review the works of Joshi and Morgan (1998; 1999, 2000) and others. Future experiments involving spectral quality and its effects should include more data points, different lamps and perhaps different coral species. Clearly, more work is required before we have an answer to the "best lamp" question. For now, it appears that spectral quality might be subordinate to lamp intensity.
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