Yesterday I stumbled across a posting suggesting that ghosts drain power from flashlight batteries to make mass, which is the visible part of the ghost. I left a comment there, but it seems not to have been approved, so I'll repeat my statements here. Assuming the flashlight is powered by two alkaline long-life D cells, it has at most about 150,000 J of energy stored in its batteries. Converted to mass, this is about 1.7 nanograms, or about the mass of a grain of fine silt 9 microns wide -- about 1/20th the width of a human hair. Whatever someone may be seeing when he reports a ghost, this is clearly not it.
I dealt with similar topics here and here.