Sforno on Genesis 1:14/ספורנו על בראשית א׳:י״ד

1יהי מאורות ברקיע השמים, the planets created on the second day should now begin to function by providing light. Their influence should be concentrated on the “lower” universe, as it is visible to us with our senses. Everything mentioned in this paragraph refers to sensations perceived by the creatures on earth. By traversing pure waters on the way to earth, the light refracted by these luminaries is increased manifold.