I've pondered on this for a while and I think I have it. There are 2 ways to approach this. Use what we know of the science of light and dark to understand the spiritual principles of light and dark in the Bible or we can do the inverse and try to understand the physical aspects of light and dark through the spiritual principles. The latter is much harder to do but i did read some stuff on Black holes and light that can be interesting to come at from a biblical view first. Anyways I think its easier coming at it from a physical view first which makes perfect sense to do and I get what you are saying Zech. However I don't think its entirely correct.
In God there is no shadow or light of turning. Lucifer's name means light bearer. His name implies his job which was to bear/spread the light. He was perfect until iniquity was found in him. When he disobeyed God he fell and evil was born. Just want to drop here and say why would God form the heavens perfect and the world in a form absent of light which is most unlike him being the father of lights and all? Anyways, moving on. In the analogy of light and dark I believe Satan "cast" the first shadow. If the language of creating darkness as its own entity bothers you then think shadow. Evil or darkness is the result of disobedience. A willful rejection of God's light. Choshek, the word translated to darkness also means obscurity, distress, dread, terror, evil , sin, sheol and of course death. All of these are the result of disobedience to God. When we sin we too cast a shadow like Satan. We create evil inspite of God's light. Satan was the first to "cast" a shadow but he no longer carries light hence the name change. Satan or opposer/adversary has the exact opposite traits of that of a light bearer. He is the embodiment of darkness. In Jesus there is no darkness, in Satan there is no light. Satan is a real being so to say he doesn't exists, the evil he creates doesn't exists and darkness doesn't exists is an error. If the darkness being the absence of light and not its own entity bit is the trip up then think of the blocking or rejecting of the light as evil and darkness as the result.