Yes the entire creation mythos is described. Literally the only dark things are evil things. Darkness is such a compelling attribute in that mythos that in of itself it spawned a demon - Shelob. From which the spider in The Hobbit descends. In Tolkien's universe, darkness is a metaphor for evil. As we know all of the people created, there are no dark people, only dark creatures. In this way, it is good vs evil, white/light vs darkness. Light/white is a recurring theme.