Lightness constancy is a visual perception phenomenon where the perceived brightness of an object remains relatively constant, despite changes in illumination. This means that a white piece of paper will still appear white whether it is in bright sunlight or dim light. Our brains adjust for lighting conditions, allowing us to recognize objects consistently. This ability helps us navigate our environment effectively. For example, when viewing a checkerboard pattern, the squares may look different in brightness due to shadows, but our perception compensates, allowing us to see the squares as having the same lightness. This is crucial for object recognition and depth perception.