A. P. Lopukhin. Explanatory Bible (Saint-Petersburg, 1904-1913):

“And God saw ... that he was good ...” So, according to the Psalmist, “the Lord shall rejoice in His works” (Ps 104.31). Light is here said to be "good" because it is the source of joy and happiness for all living beings.
"And God divided the light from the darkness." By this, God did not completely destroy the original darkness, but only established the correct periodic change of it with light, which is necessary to maintain life and preserve the strength of not only humans and animals, but also all other creatures (Ps 104.20-24; Jer 33.20-25; Jer 31.35 ).