What is this equation

1. Sep 20, 2009

ATPenergy

What is this equation I$$\gamma$$=($$\Gamma$$N)/D2

It is about Intensity of ray.
But I can't find any information about it.
What is it? And where can I get the information?

2. Sep 20, 2009

tiny-tim

Hi ATPenergy!
I'm not sure, but it looks a bit like irradiance = radiant flux (or radiant power) per area