What is the “light” that God created on the first day (Gen 1:3), particularly if not the Sun (created on the fourth day)?

The way to make this narrative cohere best both with common sense and with science is to envision the events of the narrative unfolding from a point of view on the very early proto-earth, making use of human-type perceptual equipment, not from way out in space or from some abstract, scientific point of view. Hence, we can imagine the light from the sun shining through the proto-earth’s gas cloud, there would be periods of light and periods of dark, as the gas blob began to rotate (Gen 1:5). Atmospheric conditions at some early point might well be such that there were no distinctive clouds visible from the planet surface, and so neither “firmament” nor solid ground or ocean, but merely a massive, slightly opaque dust cloud. So in fact the “light” might have been the Sun, but enshrouded by clouds of as yet unthinned and un-”divided”, formless dust and ice. Another possibility, that strikes me as being a little too anachronistic, is the notion that this is the light following the Big Bang. This general theory is explored in more detail below.