[Al Skierkiewicz]

Dan, the Spike is actually two relays powered from the input voltage. There are opto isolators on the input as Eric mentioned. You won't find a schematic, IFI doesn't publish that. If you look at the manual you will see the truth table for relay operations. This version can make either output at common or either output at + volts. Old versions (from about 2002 and earlier) did not have the full functionality.
Edit..
BTW, relays usually can stay energized when the voltage falls well below the operating voltage. The problem is pulling in at low voltage. Often the relay is speced to always pull in at a specific voltage. Often that is below the operating voltage specified.

In thinking about this, a LED ring is a custom circuit. There is nothing preventing one from using a transistor switch triggered from a digital output to provide either power or common to the LED string to turn it on. This would be considered part of the custom circuit as well. You can then feed it from the PD through an appropriate breaker to protect the wiring and custom circuit.