“Make sure that the light you think you have is not actually darkness. If you are filled with light, with no dark corners, then your whole life will be radiant, as though a floodlight were filling you with light” (Luke 11:35-36, NLT).
These verses from Luke are an extension of Jesus’ well-known teaching from the Sermon on the Mount in Matthew 6:22ff. Light and darkness are metaphors for good and evil.
But, Dr. Luke develops the metaphor more richly in his account by elaborating on the properties of light, specifically, the magnitude and direction of the light. Light travels in a straight line and if it is not bright enough or is deflected by a surface, its radiance diminishes and it can leave dark corners in a particular space.