Robert J. Alden argues that "Lucifer" in Isaiah 14:12 is not a reference to Satan; it is a reference to the "proud but now fallen king of Babylon."
Robert J. Alden, “Lucifer, Who or What?” Bulletin of the Evangelical Theological Society 11 (Winter, 1968), 35-39
To summarize and conclude let us simply note these salient factors. Lucifer is a perfectly good translation of hll in Isaiah 14:12. The meaning "light bearer" or "day star" is suitable. But the chapter deals solely with the downfall of the king of Babylon and this verse in particular. That Satan inspired the wicked king even as he rules all degenerate men is undeniable but that is quite different from saying Lucifer is Satan. The morning star is something beautiful to behold and has a most noble task in the heavens, that of announcing the new day. The king boasted that he was as great as God and Isaiah likened him to that star which is beautiful for a moment but quickly eclipsed by the glory of the sun itself. That Satan made such a boast is not known. We have no more justification for such an identification here than we do in Ezekiel 28 where the king of Tyre is in view. Lucifer is only the proud but now fallen king of Babylon.