LUMEN, why inside a closed room I can even see lighting instead that darkness?

[Arkiras]

@Anthony_Attwood

This leads to a major problem though. Due to this error, we can no longer use meshes with one side such as half the cliffs in megascans asset library as they only have front faces. The light from lumen just blasts right through the back faces and the shadows you receive look like cut-out squares

Yeah you can… all you have to do is put a rescaled cube (or any other object) on the other side to block the hole.

Using a two-sided material is the worst solution to this problem, it will cause light leaking from shadowmaps