If the Villas Boas case is to be believed, his observation indicates that these are bright areas of the surface of the object rather than incandescent lights as we know them. Further, assuming the validity of the Petit-Rechain photo from Belgium, we can see that the tips of a triangular UFO show lights which may also be attributable to a plasma phenomenon. In that photo, one can observe interesting striations of density in the light, and wisps which appear to be partly detached from the source. Beams appear to fall into two classes - normal and slow. Slow beams, as observed at Trancas, Argentina , seem, on the other hand, in view of their slow propagation, to certainly be some sort of plasma phenomenon.
Material remains luminous for some time after falling away from the object.
It seems more likely that this is a luminous or molten liquid. UFOs must input energy into the near surface area to generate an atmospheric-ionization style luminosity. Further, it is possible that maintaining this ionization even when not in the full body state would make it easier to go to the full body state. The maintenance of this ionization might also benefit from the injection of ionized atoms or molecules into the sheath, much as a gas laser sometimes requires replacement or refreshing of its contents. This may explain the occasional chemical odors and the occasional presence of apparently chemical-related burns and rashes in close encounter cases.