Hey @TinyTracker1!
The best way would probably be to go into your level BP, make an array, and add all your lights in the level to that array. Make sure they all have the same parent class that has a “Light switch” variable so you can make that the base and not have to cast to each type of light (Casting only makes something act as a more specific version).
Then, as part of the level, you can run a Custom Event to grab that array and “ForEach” body-> “turnOff” Function. For style points, you can have a variable on each that says whether it was turned off before, and save that value, then after a bit, tell each to turn back on or don’t based on that variable!