I actually made a video about one way to do this not too long ago because someone had a similar question 
https://www.youtube.com/watch?v=HXVeu2-vmaw
Keep in mind that there is a fairly easy second way. Instead of using tags like I did in this video (because of how that user worked) you can also just make the array variable of the lights “Editable” and then in your level click on your switch (or whatever), go under defaults, add an element to the array and then you have the option to pick an object from your scene to create a reference (just click on the pipette icon right next to the element).
I hope this helps
Cheers!