Lume is the luminescent material applied to watch hands and indices so the watch can be read in low light. Early lume used radium (highly radioactive, used into the 1960s), then tritium (mildly radioactive, 1960s–1998), and is now Super-LumiNova or LumiNova — photoluminescent and chemically stable. Original lume that has aged into a creamy or amber patina is highly prized by vintage watch collectors.