Can't create a dark room?

I would like to create a completely dark room but I’m not entirely sure how to achieve that. Eventually I would like it to be lit with a flip of a switch and a point light. I don’t want a completely dark scene. I’ve scoured the internet but I can’t seem to find a solution anywhere. This is what my room looks like with a ‘brick’ BSP in front of my window to demonstrate that it has virtually no effect on the lighting. My lighting is built with production quality, all of my walls are 20cm thick and touching. I have a LightMassImportanceVolume, Skylight, DirectionalLight, AtmosphericFog, and a ReflectionCapture. Any help would be greatly appreciated. Thanks!