As children, we learned how to keep darkness away by turning on a light. Sometimes, when our parents went away for the evening, we would turn on every light in the house! We understood the physical law that is also a spiritual law: light and darkness cannot occupy the same space at the same time.
Light dispels darkness. When light is present, darkness is vanquished and must depart. More importantly, darkness cannot conquer light unless the light is diminished or departs. When the spiritual light of the Holy Ghost is present, the darkness of Satan departs.
Excerpt from Elder Robert D. Hale’s April 2002 General Conference address, Out of Darkness into His Marvelous Light. Elder Robert D. Hale’s is a member of the Quorum of Twelve Apostles of the Church of Jesus Christ of Latter-day Saints. View Elder Robert D. Hale’s full address here.