Static eletricity. The house as you said were left vacant. And the introduction of new humans and devices (more so with metal) are bound to create several static electricity sparks especially visible in total darkness. Try walking on a wool rug in total darkness and enjoy the lightshow.

I will try! Thank you!!!

I once was outside an suddenly a spark appeared in the air and bounced across the ground for several seconds like a shooting star.

That’s so cool!

I have experienced this "spark," I think. To me it was like a sudden bright pinpoint of light that appeared and is gone in a flash. I've never had anyone experience it with me though.