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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.

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If you don't have to worry about interference just add the luminosities. The luminosity is just a power per unit area, and the total power will just be the sum of powers of all the incident beams.

If you have to worry about interference you need to calculate the path length from A to P and B to P. However to get interference requires coherent light sources. Assuming this is a homework question, the question should make it pretty clear if the sources are coherent and therefore if you need to consider interference.

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Nope, not a homework question. And fortunatly what I am working on does not need to worry about interference nor is it coherent. I am working on a simulator for automatically managing light levels in a great hall given outside light sources (skylights) and controllable light sources (light bulbs). They don't need to be exact results, I just wanted to make sure I was simulating things close to real physics. –  BryanLemon Jun 7 '12 at 18:02

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