God has always existed. God is light and abides in unapproachable light. Light was not created. It was commanded to shine on the darkness filled earth on the first day of creation when God started replenishing this earth.

The Sun, moon and stars came into being on the fourth day of creation!

And God said, “Let there be lights in the firmament of the heaven to divide the day from the night; and let them be for signs, and for seasons, and for days, and years: And let them be for lights in the firmament of the heaven to give light upon the earth”: and it was so. And God made two great lights; the greater light to rule the day, and the lesser light to rule the night: He made the stars also. And God set them in the firmament of the heaven to give light upon the earth, and to rule over the day and over the night, and to divide the light from the darkness: and God saw that it was good. And the evening and the morning were the fourth day. – Gen 1:14-19.

In retrospective, was there light even before the Sun, Moon and the Stars were created? Yes, because God is light, and He is eternal. The Scriptures say that God commanded light to be on the earth on the very first day of creation. And God said, “Let there be light”: and there was light. – Gen 1:3. Why was this light required? Because the earth was without form, and void; and darkness was upon the face of the deep. – Gen 1:2.