In the post we define the function R(w) to be Radiance, the incoming light along direction w. (How can your definition of radiance depend on… radiance?)

The problem we are trying to solve is to compute Irradiance (outgoing light) in terms of the Radiance (incoming light). This requires a hemispherical integral.

]]>I always thought irradiance is Integrate[(n.w)*R(w)*dOmega] and radiance is Integrate[fr*(n.w)*R(w)*dOmega]. Assuming Lambertian BRDF, fr will just be (1/Pi). Is my understanding correct, or do I miss something?

Thanks.

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