Blue Iris

I am wanting to automatically turn on an independent light source whenever a specific camera is selected in the UI3. I know how to do the light operation part if I can get an MQTT signal from BI.

I think UI3 is a third party (BP2008 ?) add in to BI5 so that may not be as easy as you hope. I suggest sending a message to support, and maybe try to PM BP2008.