I have found a great way to add lights to your building with out them being seen and gives a great effect.
This Picture shows how dark it is outside and no light visible outside
This picture is inside the building looking up still no Light’s visible
Last how you do it In this Picture you will notice the Radium Light is placed in the very far right middle of a triangle. When you do this you can now cover it it with another building block. Thank you and enjoy!