atmanam ca didrksatah
nirbhinne hy aksini tasya
jyotis caksur guna-grahah
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Thus when everything existed in darkness, the Lord desired to see Himself and all that was created. Then the eyes, the illuminating god Sun, the power of vision and the object of sight all became manifested.
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
The universe is by nature dense darkness, and therefore the total creation is called tamas, or darkness. The night is the real feature of the universe, for then one cannot see anything, including oneself. The Lord, out of His causeless mercy, first desired to see Himself and all the creation as well, and thus the sun became manifested, the power of vision for all living entities became possible, and the objects of vision were also manifested. This means that the whole phenomenal world became visible after the creation of the sun.