Need a 240VAC logic OR gate
You can just wire two 240VAC relays with one coil across each lamp and the normally open contacts in parallel. That will work even if you have the lights on a timer. 







simulate this circuit &ndash; Schematic created using CircuitLab

Functionally, that's all you need. 

You may have to consult someone familiar with the electrical codes wherever you are in order to get an installation that measures up to requirements.