Or HaChaim on Genesis 1:15/אור החיים על בראשית א׳:ט״ו

1And they will be for luminaries: The meaning of the verse is to tell that God commanded the light of the luminaries to break through the heavens and also to illuminate the earth; the explanation [of which] is that the luminaries should illuminate the entire expanse of the heavens and that their lights should also reach down until the earth. Also, it means [to teach] that God set them up, such that the strength of their light is in the heavens, and from that light that spreads out in the heavens, the earth is illuminated; as the earth does not have the power to withstand the strength of the light of the luminaries. And that is why it is exact to say, "to the luminaries in the firmament of the skies," the explanation [of which] is that they illuminate there; and its stating, "to illuminate on the earth," the explanation [of which] is that from the clear light of the skies is the earth illuminated.

2And according to [the] words of [the Sages] (Chagigah 12:), of blessed memory, that the luminaries are in the second firmament, the luminaries only break through the [first] sky and the second sky shines upon the earth. And what they, of blessed memory, stated (Yoma 28b), "A cloudy day is full of sun," is not a contradiction to our words; since, in any case, even if the place of the sun spreads the power of the sun to its sides, there is a difference between [that] and the place that the sun is fixed, where it is more powerful. And a cloudy day goes back and spreads the power of the sun that remains directed at the earth - according to what [the earth] can endure - and, because of the clouds, spreads it at the top of the skies, and that is [what is meant by] "it is full of sun."