Thanks for the info.
Actually Im looking for a method to simply alter the
brightness (full or offset-value) for each vertex.
But Im not really into all that low level rendering stuff.
To I think I have to pass on that. (Im more proficient in AI and
gamelogic programming)
The basic Idea behind all this is to have a worklow
to archive screens like this:
(yes, saw that recently in Morbius)

Kind of very old and classic 3D scenes.
Where the "shadows" are actually just realized by altering
Vertex-brightness, without fancy mixing of Textures.
The good thing is, that is is very fast.
So with a method to alter the vertex-brightness it is
realively easy to create a level-editior that generates
"Block/Grid" based levels, and creates a simple shadoweffect
on some of these blocks. Thus creating a fast and flexible
elumination/shadowing of the scene without any dynamic lights etc.
But realizing that myseft goes a bit too deep into
the rendering-procedure for me.