Light illuminating through a two sided plane

Development Rendering
1

I have a plane that has displacement and a cobblestone texture. I enabled two sided shadows on the static mesh (And in the material) and that fixes the shadows and most lighting.

However, with a point light behind it I can still see its color shining on the material (As if its illuminating the backside?) but the light does not continue past the wall, so it is stopping the light somewhat.

image

How can I fix this?

2

By using solid geometry instead of planes…
To avoid leaks you need approximately 2.5uu with on a closed volume (6 faces).

Even trees will light up like a lightbulb if you place the directional light under the landacape and they protrude…