Strange shadows in V-Ray

I am working on my first time model in Rhino and first time with V-Ray. I have got something like this
Most important question is 1
Why it looks like I have two sources of light which give shadows falling in different angles? I have only the sun.

2 I know now. One face has got a texture and this is a reason it looks darker.
3 and 4 I know now too. It is because I used Cellular texture and GPU rendering. It looks like it is not a good idea to use this kind of textures. Is it?

Sorry guys, it was another sun actually, what I didn`t know about :slight_smile: