Material node dummy need help

Hi,

I’m trying to create a material from nodes such that it’s transparency is governed by a global normal. For instance if a face is point upwards in the global z direction the material is transparent and if the face is pointing at 45 degrees to upwards in the global z the material would be partially transparent. I can’t seem to get this working and any help would be appreciated.

Thanks in advance,
GreyBeard