It's one of the deepest ideas in our collective (un)consciousness. The Sun brings heat, makes plants grow, drives us to awaken, explore, work, create. Gods of the Sun and Moon are associated with law, arts, the mind, justice, protection, inspiration, all the things that make up the best part of being human. (And even the other nice thing about being human gets this treatment - Venus is, after all, the Morning Star.) The lightbulb coming on over one's head is the genesis of a great idea. By light we can see the world; by extension, light lets us confront evil and destroy it, both within and without ourselves.