Genesis 1:3
ESV - 3 And God said, "Let there be light," and there was light.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
The light was the glory of God
If God said the light was day and the dark was night where did evening and morning come from?
In my opinion the referral to light in Genesis 1:3 is the light from Jesus. Jesus is described as being the light and the author and creator of all things.
This question is often asked by the Atheistic community as it supposedly disproves Genesis. The typical statement is "How can there be day and night without the sun". If God is the light then he himself can use that light to make light over the face of the earth. To support this theory all we need to do is look at Genesis 1:14 when God creates "lights in the expanse of the heavens to separate the day from the night".
We have to realise that we will not understand the full details of how God created everything we see around us. Its due to his divine authority that he can defy the rules of Physics and nature because he is the creator God.
Hope that helps.