Researchers have addressed light quality and its effects on zooxanthellae and coral growth. Perhaps the most interesting is a paper by Kinzie et al. (1984); they presented evidence that corals grown more rapidly under blue and white light of the same intensities (~12% of solar Photosynthetically Active Radiation - PAR, ~250 µMols·m2·sec, or 10,000 lux) than under "green" or "red" light of equal intensities. These scientists used clear or colored acrylic filters and natural sunlight. The blue filter transmitted wavelengths of ~ 400 to 500 nm and the clear filter (transmission quality not shown in the paper) likely was a fair representation of sunlight (although most acrylics attenuate all wavelengths but tend to decrease violet and blue disproportionately). "Blue" light is suggested to have some rather "magical" properties - it has been noted to increase rates of protein synthesis in some algae, as well as cause shifts in photosynthetic pigment concentrations in zooxanthellae. Blue light has also been reported to increase rates of photosynthesis (Kinzie and Hunter, 1987). Are spectral characteristics of "blue" metal halide lamps sufficient to promote photosynthesis more efficiently in zooxanthellae of captive corals?
Unfortunately, the spectral qualities of light transmitted by these researchers’ filters only faintly resemble those of lights used over aquaria. It is a leap of faith to apply the results obtained under filtered sunlight to artificial light sources, which have spectral spikes. However, this has not stopped many from interpreting that higher Kelvin lamps are best for promoting photosynthesis in corals.
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