The Phong Reflection Model (named after Bui Tuong Phong), sometimes referred to as Phong Shading, is an empirical model based on his informal observations, not physics. It includes ambient, diffuse, and specular terms. For details, see:

http://en.wikipedia.org/wiki/Phong_shading

The diffuse term or component in this model is called Lambertian Reflectance. And, yes, the Poser Diffuse node implements this math, which is very simple. That is the key value of the Phong model - it is cheap to compute.

Kd in the Phong model is Diffuse_Value * Diffuse_Color in Poser.

The Specular channels in the Poser Surface (as well as the Poser Specular node) implement the specular components of the Phong model.

And, of course, the Ambient channel in the Poser Surface, as long as you don't plug anything into it. The Alternate_Diffuse also happens to implement Ambient if you happen to plug a constant color into it.

Paradoxically, the "Phong" node in Poser does not implement the specular term in the Phong model. It implements something nobody should use except for hacks not worth explaining.

 

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