Several things, but yes. It has to be created. It cannot be the sun, moon or stars. It is not "Chaotic light" as many theologians suggest (God is a God of order). It cannot be Christ. Lucifer seems to fit. Created being. Domain of earth. Creature of light, his name literally translates to "Morning Star, Morning is often interchangeable with "Beginning", etc. I would love to be wrong on this.
Point for PL. If we apply normal interpretive rules, it won't work either. The intended audience would have understood this to mean the sun...
I've never heard of Lucifer being the light at the beginning. While I am loathe to concordism, if I were to do that, I would say it's the energy of the Big Bang.
Lucifer as the light would be an interpretive stretch: 3 And God said, “Let there be light,” and there was light. 4 God saw that the light was good, and he separated the light from the darkness. 5 God called the light “day,” and the darkness he called “night.” And there was evening, and there was morning—the first day. I don't see why it isn't just light ¯\_(ツ)_/¯
A cosmic event of some kind would be my best guess. Stars aren't the only things that generate light (an easy example would be thunderstorms) so that cosmic event could be a singularity 'exploding' (like a 'big bang'), or some other phenomenon. If it were the 'big bang', then we'd have the same progression that we see in Genesis: initial creating act --> light --> sun, moon, stars, etc. The 'natural history' of the universe would follow the same progression, and while I'm also not too big a fan of concordism, I'd take this as an instance where Scripture can be legitimately interpreted along these lines, rather than simply forced into a prevailing natural(istic) narrative. (A progression that is lost on anyone who points at Genesis and laughs at light preceding the sun.)
And light is the absence of darkness. But the question was why. As for a possible explanation, the darkness represents the fallen state of Lucifer and those who joined him in the rebellion. So quite the opposite of the OP
Yes, but not in the same way that darkness is the absence of light. Light is a thing: photons; darkness, on the other hand, isn't anything at all, but the lack of.