I have the K4 Vegetation Pack from the store and have noticed that when importing the grass model fbx files the models remain unlit as far as direct lighting is concerned, in other words the lighting remains constant all around the models regardless of the angle of the Sun.

I suspect that due to them comprising just a few angled planes this is maybe to avoid odd lighting effects if the planes responded to direct lighting, but my question is ... how is this accomplished? It doesn't appear to be related to the shader in use or any particular material setting so I'm guessing its inherent in the model itself.

Not being a modeller I have no direct knowledge but I assume its something to do with the normals, as if I import it into a modelling app and export without the smoothing groups then the imported model now responds to the direct lighting.

Just something I'd like to understand, if someone would be kind enough to explain, as it seems a useful technique to make use of at times.

For flat planed grass I do the following:
-set vertex normals up (first turn on preview of vertex normals using Alt+V and then Alt+N, then in Mesh Editor \ Operations \ Align Normals Up - a few times)
-set Material Technique as "Grass" (not "Grass 3D")

Brilliant! Not only explains it but gives me the tools to accomplish it. Many thanks for the swift response.