what is "light"

If God created "light" on the first day, but did not create the sun, moon, and stars until the fifth day. What is "light?" Everything that produces light was not created until later so what does that mean? This following passage is from Donald Miller's book, Through Pained Deserts. Not sure if it answers my question or not.

"In the Hebrew tradition, which splintered off into the Christian tradition, which is how i was raised, light is a metaphor God makes a cosmos out of the nothingness, a molecular composition, of which He is not and never has been, as anything is limiting, and God has no limits. in this way, He isn't, and yet is. The poetic imagery is rather beautiful, stating that all we see and feel and touch, the hardness of dense atoms, the softness of a breeze (atoms perhaps loose as if in play) is the breath of God. And into this being, into this existence, God first creates light. this light is not to be confused with the sun and moon and stars, as they are not created until later. He simply creates light, a nonsubstance that is like a particle and like a wave, but perhaps neither, just some kind of traveling energy. A kind of magnetic wave. Light, then, becomes a fitting metaphor for a nonbeing who is. God, if like light, travels at the speed of light, and because space and time are mingled with speed, the speed of light is the magic, exact number that allows a kind of escape from time. Scientists have played with atomic clocks, matched exactly, setting one in a plane to fly around the world, and another motionless, waiting for the return of its partner. When they reunite, the one that traveled rests milliseconds behind the one fixed. The faster you move, physicists have found, the less you experience time And if you move at the speed of light, you will never age; you are outside of time; you are an eternal creature. But before you strap on your running shoes, you should know scientists warn us that with speed, matter increases in density, so an attempt at the speed of light will have you imploded by the time you hit Witchita, your atoms as dense as bowling balls. And to make matters worse, your density increases on a curve; the faster you go, the steeper the trajectory on the graph. You and I, made from molecules, cannot travel at the speed of light and cannot escape time, at least not with a body. Consider the complexity of light in light of the Hebrew metaphor: we don't see light; we see what it touches. It is more or less invisible, made from nothing, just purposed and focused energy, infinite in its power (it will never tire if fired into a vacuum, going on forever). How fitting, then, for God to create an existence, then a metaphor, as if to say, here is something entirely unlike you, outside of time, infinite in its power and thrust: here is something you can experience but cannot understand. Throughout the remainder of the Bible, then, God calls himself light. The perfection of the Hebrew metaphor is eerie, especially considering Eratosthenes wouldn't play with sticks and shadows for several thousand years, discovering Ra was, in fact, never closing his eyes."

What do you think?