To answer the OPs question, yep, I saw one one time. I lived in a farmhouse built late 1700s. Whatever it was stayed in my bedroom closet and insisted that the light in the closet stayed on. If you turned it off, next time you enter the room the light is on. Never asked a scientist but 2 electricians couldn't explain it. also, there were 2 gravestones about 30 yards from the house that were so weather beaten that it was hard to read the carvings. Below one name it said "improved this land" and both had dates from 17XX really worn. Not saying the markers had anything to do with anything but it's the only place I lived where I had to mow around grave markers.