Does someone have Tips how to make a Building darker?

[Firestar97]

I'm building a Nocturnal House for Pangolins and Aardvarks and would like to know if there is a Possibility to make a Building darker. I'm not completely sure but I think, I would need to dig a really deep Cave to create a really dark Room if there is no other Possibility. I still remember how much Terrain I needed covering the Area when I've built a Nocturnal House during the Beta