For with thee is the fountain of life: in thy light shall we see light. (Psalm 36:9)
Without the light of the sun and moon, our world would dwell in darkness. And then, without some artificial light or flame to create a fire, we would have no light at all.
This is the most basic state of man. That he is dependent upon light. And not just any light. It must be of the proper type and intensity to make things grow and to keep the world at the proper tolerable temperatures for survival.