Quoting Commentary for Psalms 27:1

...The first question is in the verse "in the beginning God created" etc. It is that if the text was coming to tell the order of the creation and what came before, why would it say that the First created heaven and earth. For in them you will find that which physically exists above and below. If all this was created in the beginning, what was it that was created afterward? And the commentators ... this in the saying that the text did not come to tell us the order of creation ... You should say: in the beginning of God's creation of Heaven and Earth, the Land was Void and Nothing. This is the way of Rashi and Ibn Ezra. Ralbag is close to them if not that he makes ... with the saying "let there be light." The text speaks according to its thought "In the beginning God created Heaven and Earth and the Earth was Void and Nothingness ... God said let there be light." This explanation does not appear entirely correct with me because it would it would obligate that the text ... On the first intention creation to Heaven and Earth that is the essence ... and its faith.

You should know that this “visible” light is what is called טוב, “good.” It is this light which David referred to in Psalms 31,20 when he mentioned the “goodness G’d has in store for the righteous and added the words: ‘in full view of man.’” He referred to the kind of light which had become visible. There are numerous references to this light commented upon by Midrash Tehillim 27 on the words קל ה' ויאר לנו “G’d is powerful, He shone for us;” or ה' אורי וישעי, “G’d is my light and my help.
You need to appreciate that the real beginning of the creation of the physical universe commenced with this directive of “let there be light.” This occurred on the 25th day of Ellul, the number 25 corresponding to the numerical value of the word יהי. As to the statement in the Talmud (Rosh Hashanah 27) that the world was created in the month of Tishrey, the reference was to the creation of Adam, the first human being. Creation of man constituted the completion of the creative process and this is what the Talmud referred to. Man is the “seal” of all of G’d’s activities up until then. The Talmud could not say that the universe was created in Ellul as it concerned itself with a finished product only.

He shone a light in the darkness Heb. זרח [the “kal” conjugation], like הזריח, [the “hiph’il” or causative conjugation]. Its midrashic interpretation is that He Himself, so to speak, becomes a light for them, as (above 27:1): “The Lord is my light and my salvation.”