Let there be light
1:1 In the beginning God created the heaven and the earth.
1:2 And the earth was without form, and void; and darkness [was] upon the face of the deep. And the Spirit of God moved upon the face of the waters.
1:3 And God said, Let there be light: and there was light.
1:4 And God saw the light, that [it was] good: and God divided the light from the darkness.
1:5 And God called the light Day, and the darkness he called Night. And the evening and the morning were the first day.
Book of Genesis
God's will: Let there be light
Another possibility would be the landing of Noah's Ark, ending of the Flood, first rays of sun after 40 days of rainstorms and a rainbow on the sky.