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Re: light attenuation

To Roger:

Thanks, Roger, for the table with attenuation values. Worth saving for
future use ! Integrating the "pure H2O" curve in the article to estimate 
the PAR attenuation, I get 5% (at 16") ! This is consistent with your data.

This discusion started with Wright's comment about the "*no* effective 
attenuation of the photosynthetically active spectrum in clear tanks that 
are less than a few *meters* deep". I looked into the absorption curve of
pure water in that article and found that the red region *is* significantly 
attenuated. So that conclusion still stands in the ligth of the new data.

To Merril:

I was trying to say that absorption in the blue is negligible in clear water. 
That's why corals (that evolved typically in deeper and clearer water than 
freshwater plants) are able to use it. In the red, on the other hand, even
clear water seems to exert a significant attenuation. What that means for 
plants is of course another issue. I was wondering if it has any significance
at all. Most aquatic plants evolved from land varieties, and most live under
seasonal cycles where the water level comes up and down. For a significant
part of their life cycle they live emmersed, or submerged under a thin layer
of water. Maybe in the end the best compromise is to stick with full-spectrum,
sun-simulation ligth ?

On another point, the baby ozelot sword you gave me grew to a monster size ! 
It produced a half dozen babies so far, that for lack of room, I'm growing 
in the garden pond. Thanks !

- Ivo Busko
  Baltimore, MD