[A separate etymology says Λουκᾶς/Λουκανός, derived from a term meaning "man from Lucania". But I'm not particularly concerned with that supposed etymology in this question]
Elsewhere (reading about Leucism in biology (white stag)) I came across the Geek word λευκός(HGL) and wondered if that was not a more suitable or a cognate etymology, and found the Greek name Loukâs (Λουκᾶς) said to be derived from it.
Both Lux and Leukos have the same Proto-IndoEuropean etymology of *leuk-, meaning "bright", "to shine", "to see".
In De Praenominibus (Concerning Praenomina), Julius Paris asserts that Lucius is derived from lux, light, and that the name was originally given to children who were born at dawn.
Can anyone discover or deduct from historical records what came first: the Latin Lucius from Lux, or the Greek Λουκᾶς from Λευκός? Indeed, perhaps there was a PIE name *Leukos which predates them both! Perhaps an Etruscan or Umbrian origin that someone can find?