I kept seeing movement in this clip but could not focus in on it. I had to increase the brightness to see and it appears to be a small orb which emanates from the wall and disappears under the stairs very quickly. But the more I look at it, it could be a manifestation. There's allot of centralized movement on the bottom of the stairs that the camera was trying to auto focus on. The camera is positioned on a stair looking up so what you are seeing is the bottom side of the stairs above. Again, we are in total darkness. It was pitch black and what you do see is a result of the IR camera and IR lighting I was using.
http://www.e-southerndata.com/staugustinelighthouse/small_orb.wmv