Assuming 2LoT holds and the vampire is unable to reach thermodynamic equilibrium with its surroundings (rate of energy loss too high), then the energy of subsequent R and S photons will decrease as they carry away energy from the vampire.

A fail-proof vampire detector could then be constructed. In any brightly lit room, the vampire will be the inky black shape.

Hmm, perhaps an illuminated, observed vampire would be an almost perfect cold load for heat engines.