On the basis of our daily experience, we conclude that there can be no light without the presence of the sun or moon (or artificial light). When God made the world, however, he made light independent of the sun (Genesis 1:3) and did not connect light to sun (and moon) till the fourth day (Genesis 1:14). Since he himself is light he did not need the sun to provide light. In the New Jerusalem, God will be so richly present that he will outshine the heavenly bodies that he had used for centuries as his means for lighting his world; sun and moon will no longer be needed.
23 And the city has no need of sun or moon to shine on it, for the glory of God gives it light, and its lamp is the Lamb.