Is there a solid state relay that will do this?

[gadget-evilusions]

I am building some lights, that when power is knocked out will get power from a 12v battery pack and illuminate. I plan on using a relay between the battery and led light board. Is there a solid state relay type that will keep the circuit open as long as I apply 12v to the input of the relay, and then if the 12v supply is lost, will close the circuit between the battery and leds? I know I can use a mechanical relay but these will be powered for about 6 weeks straight while our haunted house is open.

[JonnyMac]

I don't think so, Brian.  What you need is a normally-closed relay, and so far as I know DC SSRs always act like normally-open.

[JackMan]

There is such an animal. DigiKey has some SPDT and N.C. solid state relays but they might be specail order. Here's some info on another 12VDC SPDT solid state.