One of the main differences between Luciferianism and Setianism is the symbolism of Light vs. Dark. In Setianism, darkness is a positive thing, one that allows for freedom and growth, whereas the solar aspects of mythology are seen as ignorant and limiting. Luciferianism has the opposite symbolism, where light represents knowledge and growth, and dark represents ignorance and stagnation. This does not mean the ideologies are opposed, and indeed both are part of the Western Left Hand Path, but the exoteric aspects of the two religions are basically reversed. This is, of course, a subjective preference and choice the individual is more than welcome to make in the Left Hand Path – whatever works best for you! Luciferianism is also mainly focused on external objective knowledge, whereas Setianism is focused on discrete individual existence.
Luciferianism is also not inherently theistic, same with "Satanism" as a whole. Many Luciferians utilize Luciferian symbolism without believing in the literal existence of metaphysical reality. This is similar to LaVeyan Satanism, but rather than a focus on carnal/material desire, the Luciferian would focus on knowledge and intellectual growth. Of course, there are also Luciferians who are theistic, both who think Lucifer is a specific being and those who believe it is a title for numerous beings. Much of theistic Luciferianism is similar to Theistic Satanism, just with more of a focus on light over darkness. Again this is simply exoteric, all three groups are aspects of the Left Hand Path.