A built-in light meter is a reflective light measuring system integrated directly into a camera, allowing photographers to determine correct exposure settings automatically or with guidance. It measures the light reflecting from the scene as seen from the camera's position, helping to set the appropriate aperture, shutter speed, and ISO. Built-in light meters make it quick and easy to achieve accurate exposures, and are a standard feature in most modern digital and film cameras, supporting both automatic and manual shooting modes.