Photons per Square Millimeter per Second
In the visible spectrum, how many photons reach the Earth per square
millimeter, per second? (Assuming a nice, clear day with the sun nearly directly
This is not an easy question to answer because it depends upon many variables.
Even "assuming a nice, clear day with the sun nearly directly overhead, etc."
First, you have to integrate over the visible region of the electromagnetic
spectrum. Second, both water and oxygen have absorptions in the visible range --
weak but present in the long path length of the atmosphere. And these are just
the start of the complications. The NASA web site:
gives the basis for determining the answer, but you will need a long sharp
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Update: June 2012