I'm very new to this forum and a bit decrepit, so I apologise if I do anything wrong.
I've created a simple room building scene. But there's a strange problem with the lighting. As you can see in the image below with no light added to the scene or with a light inside the box everything is okay. If I add any kind of light outside the box to the scene (point, direct, skylight etc) light stops entering the box and the scene is rendered incorrectly.
Thanks very much if you can help, Gray