In the Word, “light” in the highest sense represents Divine Truth: knowledge, ideas, understanding that come to us from the Lord. In lesser degrees -- the light of a lamp, the light of the moon and so forth -- it represents lower levels of truth, ideas and understanding drawn from more earthly sources. Also, the sun in the Word represents the Lord, with its heat representing the divine love and its light representing the divine wisdom. That wisdom flows into our minds and enters our lives in the form of truth -- things we can know and ponder that lead us and help us to be good people. This connection between light and thought is one of many spiritual/natural relationships that's embedded in our common language. People “see the light” when they understand something; we try to “shed some light” by bringing new thoughts to a difficult question; people are “enlightened” when they get new information or a more complete understanding of something. And a light bulb in a cartoon represents an idea!

20. Verse 3 And God said, Let there be light; and there was light. This is at the outset when a person starts to realize that good and truth are something superior. Thoroughly external people do not even know what good is and what truth is, for they imagine that everything which comprises self-love and love of the world is good, and that everything that panders to those loves is truth. Thus they do not know that the things which they imagine to be good are in fact evil, and that those which they imagine to be true are in fact false. But when a person is conceived anew, first he starts to recognize that the good in him is not really good, and then, when he enters more into light, to recognize the existence of the Lord and that the Lord is good and truth themselves. The Lord Himself says in John that men ought to know He exists,

Unless you believe that I am, you will die in your sins. John 8:24.

The point that the Lord is good itself, which is life, and truth itself, which is light, together with the consequent point that no good or truth exist except from the Lord, is made once more in John,

In the beginning was the Word, and the Word was with God, and the Word was God. All things were made through Him, and without Him was not anything made that was made. In Him was life, and the life was the light of men, and the light shines in the darkness. He was the true light that enlightens every man coming into the world John 1:1, 3-5, 9.