This is a running motif throughout the novel, and it corresponds pretty well to the typical light = goodness and truth, dark = bad and deceitful construction. For example, during Orlando’s carriage ride with Alexander Pope, she’s still completely enamored by poets and writers. When Orlando glances at Pope in the half-light, she thinks all sorts of outrageous compliments of Pope: boy, what a genius! Look how incredible he is! When the carriage passes under a streetlight, however, Orlando "sees the light" so to speak, and realizes that Pope is actually quite an ordinary person. She switches her opinions back and forth throughout their carriage ride – darkness means Pope is awesome, light means that Pope is ordinary. Of course, it is the latter that turns out to be true.