It appears that some people consider "Luciferian" to be interchangeable with "Satanist" and "black magician." I've tried to define it previously (here), and I now realize that I overlooked another significant possibility (mentioned below). Rudolf Steiner (whom some would probably consider to be a "Luciferian" because he used his clairvoyant powers to delve into Lucifer's influences in great detail, and found that they're not all evil) actually considered himself to be a Christian, and he set out to purify Theosophy and make it the legitimate heir to true Rosicrucianism, which was a genuine Mystery teaching, unlike the Venetian counterfeit. (He also considered it possible that Satan will be redeemed eventually, but he has indicated that the Devil is irredeemable.)
Considering that the 8th Sphere is Lucifer's ultimate agenda, it seems to me that one way to define "Luciferian" would be someone who assists Lucifer in this endeavor. Lucifer's part in this effort is to attempt to lure mankind into adopting an escapist mindset totally involved in pure fantasy, while Satan's part is to create a mechanistic world order designed to drive the spirit of mankind out, i.e. by turning society in to a faceless, unaccountable machine that frustrates the human spirit at every turn. (Isn't this an apt description of the "war on terror?") So, Satan's influence would be to start the "war on terror," and Lucifer's influence would be to provide the wide variety of escapist fare, such as drugs and perhaps video games, into which we can "escape," at least in our minds. A "Luciferian," then, would be anyone who wittingly creates means of "escape" for this purpose.