Sforno on Genesis 1:4/ספורנו על בראשית א׳:ד׳

1וירא אלוקים את האור כי טוב, This describes the reason why G’d created the light, not that He “saw”” something new which He had not been aware of previously. It was because it was “good,” that G’d had created the light.

2ויבדל אלוקים בין האור ובין החשך, the days (prior to the fourth day when the sun was placed in orbit) during which use was made of the “original light,” periods of light and darkness alternated due to causes other than the revolving of the planet around its own axis, i.e. due to the direct expression of G’d’s desire. He ensured that periods of light alternated with periods of darkness.