Dionysius of Alexandria

Because the Father is eternal, the Son is eternal, since he is light from light. If there is a parent, there is also a Son. If there were not a son, how, and of whom, would there be a parent? But both exist, and exist always. Since God is light, Christ is radiance. Since the spirit exists (in fact, "God is spirit"), by analogy Christ is called emanation. Indeed, "he is an emanation of the power of God."