If I use diffuse instead of alternate diffuse everything is black.

Does Alternate Diffuse includes Ambient light?

Thank you for your help in advance.

The Diffuse_Color channel is an input to a built-in Diffuse node which takes into account incoming light to the surface.

The Specular_Color channel is also an input to a built-in Specular node, to simulate directly reflected light.

The Alternate_Diffuse channel is a direct input, without any internal light calculations. Whatever you plug into that channel will add to the surface colour without modification. The same is true of the Alternate_Specular and Ambient_Color channels.

You would do better to plug the Blinn node into the Alternate_Specular channel, and switch off Specular_Color and/or Specular_Value. If you use the Specular_Color channel for a Blinn node, you are combining two specular nodes which work quite differently.

if you have been reading the above, I have edited it to (I hope) clarify a couple of things!

Hmm, I like to ask again.

Am I right with?:
Using the Diffuse gives a complete black render if no light is active in the scene. Whatever the internal calculation is doing, it need's light from the outside (a light source and/or IL and/or AO etc.).
Is that right? If yes then I think I understood it.

But what about the Alternate_Diffuse?
The scene does not have any light source on. But I get a material that is not black (dark). As I understood it, a material only will emit light by itself if Ambient Color and Ambient Value are greater than 0. But in my example the material emits light only by attaching something to the Alternate_Diffuse (Spec. Blinn etc. are detached and set to zero now).

Putting something in Alternate_Diffuse let a material emit it's own light.
Is that right? If no, I still don't understand it.

Well I need to correct me after trying more things.

Alternate_Diffuse seems to just create RGB values according to it's input. If I just put a Simple Color node with let's say RGB pink into it, then the surface will be pink. It does not care about light.
If I put a Diffuse node instead of Simple Color into it, then the surface will be pink also, but the Diffuse node also takes care about the influence of the light (if a light is switched on).

So I think I got it.

The Poser Surface Diffuse does everything for me. The Alternate Diffuse gives me the opportunity to do everything myself.

Isao, I think that's what you said, right?

Yes, you got it!

Except one thing you wrote is not right:-

The PoserSurface Diffuse_Color channel does not do everything. It only does one thing: it implements a particular type of Diffuse node (I forget which diffuse lighting model it uses). Anything else you need - such as specular reflections, true reflections, ambient occlusion, transparency, translucence, refraction, etc. - has to be implemented separately.

Quote -
The PoserSurface Diffuse_Color channel does not do everything. It only does one thing: it implements a particular type of Diffuse node (I forget which diffuse lighting model it uses). 

It's the diffuse component Kd for Phong shading. Is that what you meant?

Quote - It's the diffuse component Kd for Phong shading. Is that what you meant?

I'm sorry, but I don't know enough about different lighting models to know if that's correct or not! Someone else is sure to know which lighting model the Poser Diffuse node implements.

In Poser at least, the Phong node implements a specular lighting model, not diffuse. I don't know if Phong means something different outside of Poser, but it wouldn't surprise me in the least.

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.

Thanks you very much for this background information.