Trying to add a light source but black spot appears

[Remuddler]

I was watching several SH3D videos on Youtube. I see that light sources can be added in front of the virtual visitor. In the videos they add soft glow emanating from the center of the source. I added a 3.5 ft diameter light source in my shower model (it is behind the glass doors in the shower). But a large black spot appears at the middle of the source. Black spots appear in all my lights (ceiling can lights made from pendant lamps shrunk to very thin vertical height). What is causing this black spots? Can I get rid of the spots? I also have a lot of noise in upper areas even in best quality rendering settings (especially in upper areas and corners).