The Brilliance Relay is a switch that allows you to control another landscape lighting transformer down the line with a single timing device, like a photocell or a Brilliance Smart Socket 3.0. You can use as many Brilliance Relays as needed in a system, and all the Relays in the system use the same initial timing device. This is helpful when you need to synchronize multiple transformers to operate at the same time. The 12-15 VAC connection activates the on/off function of the Relay device.