into something that will then switch on a series of outside lights (12v, so I want to switch on the transformer, probably just switch a 6-way power strip. Any suggestions?
You need to find out the max switching Current (Amps)of the photocell. depending on the sise of the transformer it probably wouldn't be a good idea to wire it directly to the photocell, also I wouldn't connect it to a trailing 13Amp lead.