1. pls take a look at the picture where the wall meets the floor - as you can see shadows are not aligned - is there a way to make it right?

2. wall and floor are 100%  white but I can get them white only if the light is 45deg on xRot  (in half way between them) - each deviation from that gives me gray color on one of them - is there a way to make them white while the infinite light is at different deg.?

Thanks.

if I use a prop like: wall + floor connected by that corner edge (in other words: 1 geometry) instead of 2 separate, then the shadows are ok.

This is pretty tricky. The reason you get different levels of illumination is because that's how diffuse reflection works in real life. The reflected diffuse intensity is going to be in proportion to the light energy per unit of area.

Imagine a pencil thin circular beam of light striking a surface at 90 degrees. The lit spot is exactly the same circular area as the cross section of the beam. However, if you tilt the light to a lower angle, then the lit area becomes spread out, which means the same amount of light energy is spread out over a larger area (an ellipse in this case), thus lower energy per unit area.

To counteract this, we need to do a non-photoreal (NPR) shader (material) on the wall and floor.

So, knowing that you have an IBL and an Infinite light, if I build a shader that only responds to specular light, then it only gets data from the infinite light.

Here's a shader you can try. It uses a Specular node to detect where light is striking from the infinite light. Based on that, it chooses one of two colors in a Blender. The darker one will be the shadow color, and can be any color you want. The lighter one will be the lit color, and since you requested pure white, that's what I put in Value_2.

My infinite light is at 100% intensity and the xRotate is -20 degrees, much less than 45.

You may have to adjust things if you want your light to be different. Also, I enabled Gamma Correction in Poser Pro here. Without GC, it will look a bit different.

Oh, and you probably got mismatched shadows in the beginning because the wall was not really touching the floor. If you force the wall to go below the ground a bit, then you get shadows that line up.

No matter what I do in render settings, I still get a faint line at the joint between wall and floor. I'm really not sure why that happens.

I think the only way to get rid of that is to model a single object for wall and floor, and have a very small bevel at the join, so that the normals transition smoothly.

Thanks a lot bagginsbill
it works !

I made a mistake in my first post: the angle was -45 (45 would be under the ground),
but now with your shader is not important because the infinite can be in same plane as ground (xRot  = 0) and I still got wall and ground white.

Just one more thing:
since there is no more normal Diffusion in use so I don't know where to plug Ambient Occlusion node for the wall and floor?

The idea with small "bevel" sounds good, I'll give it a try

If you plug AO in, then you're going to get an AO shadow in the crease, because the wall and floor will "occlude" each other. Is that what you want?

In any case, plug the AO into the Specular_Value of the Specular node.

Edit: so I think I'll stick to the prop without bevel - oterwise it won't be possible to get any crease at all.

I pluged that AO into the place you told
 and in addition I pluged it into blender "shadow" input - which gave stronger shadow in places where body was closer to te wall / ground.

Thanks.

One more thing:
I plugged NOISE into blender "light: node and I got slight grain on wall  / ground.

Looks like there are endless possibilities with that NPR shader.

Yep. As Olivier likes to say, when you want "something here and not there", use a Blender.