The creation of light and its separation from darkness generates the fundamental order of time that governs the rest of the chapter--day and night. The light of Genesis 1 is called "day." Day is a period of time that then gets used throughout the rest of the chapter. For example, "It was evening, it was morning, day one." Rather than recounting the creation of photons, the narrative portrays the creation of light as the fundamental order of time so that life can flourish and the narrative can progress.