what are luciferians?

Uhh, I guess people who follow Lucifer??

Luciferians describes two quite separate heterodox tendencies, one in opposition to Arianism, the other to the Roman Catholic Church.

Followers of Lucifer Calaritanus

"Luciferians" described a schismatic group named after Lucifer, Bishop of Cagliari in Sardinia in the late 4th century. The movement was linked to the complex conflict about Arianism. Arius had been condemned as a heretic by the First Council of Nicea (325). His movement, based in the Eastern half of the Empire, gained power through the Roman Emperors Constantius II and Valens but also split into various factions, of which some reconciled with the Catholic Church and accepted the Nicene creed.