Christmas Lights - neutral vs GND query

I'm planning on hooking up my christmas lights to a 5 V relay for my Arduino uno, however the christmas lights have three wires (HOT, NEUTRAL, GND) and I'm not sure whether +ve and -ve for the relay is HOT and NEUTRAL or HOT and GND?

Also, the adapter for the plug of the lights is rated 'PRI: 240V, SEC: 24-36V', is this referring to primary and secondary windings for transforming the voltage from 240V down to between 24-36V?

My apologies for my lack of knowledge. I'm really eager to learn (and also to be safe when dealing with electronics)

Thanks in advance :slight_smile:

Which relay?

But I'm pretty sure the power for the relay needs to come from somewhere else then mains. So it's neither hot (L), neutral (N) or protective earth (PE) (NOT ground/GND)

The lights only connect inline with the L to the C (Common) and NO (normally open) terminal of the relay.