BRDF

Characteristics of a BRDF

As I see it, integration of light alone times <N,L> yields the irradiance:

<math> I(\mathbf{x}) = \int\limits_{\Omega} L_i(\omega_i) (n.\omega_i) \, d\omega_i </math>

Integrating the BRDF over the hemisphere of directions must yield a radiance.

Sources

I've been reading interesting papers from the Siggraph 2012 talk about Practical Physically Based Shading in Film and Game Production which is available here

Some ideas are worth mentioning.