Here is Calvin's commentary on Isaiah 14:12 (emphasis mine):

12.How art thou fallen from heaven! Isaiah proceeds with the discourse which he had formerly begun as personating the dead, and concludes that the tyrant differs in no respect from other men, though his object was to lead men to believe that he was some god. He employs an elegant metaphor, by comparing him to Lucifer, and calls him the Son of the Dawn; (220) and that on account of his splendor and brightness with which he shone above others. The exposition of this passage, which some have given, as if it referred to Satan, has arisen from ignorance; for the context plainly shows that these statements must be understood in reference to the king of the Babylonians. But when passages of Scripture are taken up at random, and no attention is paid to the context, we need not wonder that mistakes of this kind frequently arise. Yet it was an instance of very gross ignorance, to imagine that Lucifer was the king of devils, and that the Prophet gave him this name. But as these inventions have no probability whatever, let us pass by them as useless fables.