Ok, Lets say I have two point light sources A and B. Each light source has a power Pa and Pb, and is distance Da and Db away from a point P on a plane.
I can calculate the amount of luminosity at point P from light A using the inverse square law. Likewise, I can calculate the luminosity from light B.
What I am trying to do is calculate the luminosity at point P from light A and B combined. I am not sure how to combine the luminosity from two disparate light sources.