Your right, turning off the lights is completely inappropriate for any child, but especially Mite!

Is he alright? I'm certain that was scary for him.

I hope the principal accepts this information in a professional manner and doesn't try to turn it around on you or minimize the issue!

My advice is ask him/her to address it but don't make demands as to what he/she should do about it.

Deep breathing will get you through the day.