I hope your taking this as a friendly back and forth learning experience because the last thing I want to do is make enemies or even upset people on here.
As far as the 10k vs 20k, your referring to Metal Hilides, which the 10k PAR output is much higher than a 20k. This would fall under the "intensity" of the light vs the spectrum of the light. Also, 10K lights put out more of the red spectrum, which is also used by the photosynthesis process. But there are reasons people do not run 10k or 20k MH lights alone, they are almost always paired up with Actinic CFL/VHO/T5HO lights right? They use the MH light to be able to get the intensity of the light to reach the bottom of the tank (like for clams), where as using CFLs, especially if you try only Actinics with nothing else, the intensity is greatly reduced by the distance it must travel through the water. I believe this is the reason that you can not use Actinic lights alone because it does not put out nearly enough intensity to fully "feed" photosynthetic species even though the spectrum is the most ideal for that process. With Day lights and MH lights it will suppliment the blue by adding overall light intensity as well as the red spectrum in the tank.
Again let me refer you to this: http://www.serc.si.edu/labs/phytoplankton/primer/components_phyto.jsp
"The graph depicts three typical absorbance spectra for various types of phytoplankton. As you can see, absorption is greatest in the blue region of the spectrum, with a significant peak in the orange to red region of the spectrum. Absorption is the lowest in the green region, hence the green color of the water."
I don't claim to have all the answers, or even claim what I am saying is correct, it is just what my understanding has been for many years. I don't even know how or why I think what I do, if a LFS told me, or I read it elsewhere, but I swear I am not just pulling it out of my ...
As far as the 10k vs 20k, your referring to Metal Hilides, which the 10k PAR output is much higher than a 20k. This would fall under the "intensity" of the light vs the spectrum of the light. Also, 10K lights put out more of the red spectrum, which is also used by the photosynthesis process. But there are reasons people do not run 10k or 20k MH lights alone, they are almost always paired up with Actinic CFL/VHO/T5HO lights right? They use the MH light to be able to get the intensity of the light to reach the bottom of the tank (like for clams), where as using CFLs, especially if you try only Actinics with nothing else, the intensity is greatly reduced by the distance it must travel through the water. I believe this is the reason that you can not use Actinic lights alone because it does not put out nearly enough intensity to fully "feed" photosynthetic species even though the spectrum is the most ideal for that process. With Day lights and MH lights it will suppliment the blue by adding overall light intensity as well as the red spectrum in the tank.
Again let me refer you to this: http://www.serc.si.edu/labs/phytoplankton/primer/components_phyto.jsp
"The graph depicts three typical absorbance spectra for various types of phytoplankton. As you can see, absorption is greatest in the blue region of the spectrum, with a significant peak in the orange to red region of the spectrum. Absorption is the lowest in the green region, hence the green color of the water."
I don't claim to have all the answers, or even claim what I am saying is correct, it is just what my understanding has been for many years. I don't even know how or why I think what I do, if a LFS told me, or I read it elsewhere, but I swear I am not just pulling it out of my ...
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