4" RMC trunk with 1 1?/2 inch RMC for branches on the tree . This is the design anyway.The wiring will be inside the conduit and a fixture socket will be attached to the end of each 1 1?/2 pipe used as branches. This is something an Archiect dreamed up but I'm more concerned about the safety issue with the 120 volt unprotected bulb. Low voltage is another option. Has anyone out there run across something like this before. Quirky !!