On which day did God create light?

Answer: First day

God created light on the first day, separating it from darkness.

“And God said, “Let there be light,” and there was light. And God saw that the light was good, and He separated the light from the darkness. God called the light “day,” and the darkness He called “night.” And there was evening, and there was morning—the first day.”— Genesis 1:3-5 (BSB)