Brightness constancy is a visual perception phenomenon where the perceived brightness of an object remains relatively constant, despite changes in lighting conditions. For example, a white piece of paper appears white whether it is in bright sunlight or dim light. This ability helps us recognize objects consistently in varying environments. This effect is influenced by the brain's interpretation of light and color, taking into account surrounding objects and their illumination. Factors such as surrounding colors, shadows, and light sources play a role in how we perceive brightness, allowing us to maintain a stable perception of our environment.