Quote:
The standard measure that quantifies the energy available for photosynthesis is "Photosynthetic Active Radiation" (aka "Photosynthetic Available Radiation") or PAR. Contrary to the lumen measure that takes into account the human eye response, PAR is an unweighted measure. It accounts with equal weight for all the output a light source emits in the wavelength range between 400 and 700 nm. PAR also differs from the lumen in the fact that it is not a direct measure of energy. It is expressed in "number of photons per second", whose relationship with "energy per second" (power) is intermediated by the spectral curve of the light source. One cannot be directly converted into the other without the spectral curve.
The most efficient bulbs are the metal halides, the high pressure sodium, and the tri-phosphors ADV850, Dulux, Pentron HO, and Aquarelle, about 20-30% more efficient than the average fluorescent. Of note is the comparison of bulbs with same spectrum but different power. The PC6700 with 55 Watt power is significantly less efficient than the 96 Watt version. This trend should be true for other fluorescent types as well, and also for the MH types. Interesting enough, a generic, traditional metal halide does not perform so well when put side by side with more evolved types such as the dense-line emitter MHs (MHN, Iwasaki65 and Optimarc). The HPS deluxe was included in the sample only for completeness, since it has a too low color temperature (2200 K) to be of use as the main light source in planted aquaria. It might be useful as a replacement for halogen/incandescent bulbs used as accent lights though. Normal HPS bulbs were not analyzed due to their poor CRI (around 20).
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Well, reading again more I also read contrasting information as for as efficiency, MH over VHO,PC etc, in some case studies, so I'll have to do some more reading also.