There are several synonyms for the term "luminous vapor" depending on the context in which it is used. If referring to gas that emits light, "phosphorescent gas," "radiant gas," or "emitting gas" are all suitable alternatives. "Iridescent mist" or "glowing fog" could also be used to describe a colorful or shimmering vapor. For a more technical term, "plasma" can be used to describe a state of matter in which gas particles are ionized and emit light. In a more mystical or supernatural context, "ethereal mist" or "ghostly haze" could be used to describe a luminous vapor that carries an otherworldly quality.