In a standard three-point lighting setup, what is the specific purpose of the fill light?

In a standard three-point lighting setup, the key light is the primary and strongest light source, positioned to illuminate the subject and create prominent shadows. The specific purpose of the fill light is to soften and reduce the intensity of these shadows created by the key light. It is typically positioned on the opposite side of the subject from the key light and provides secondary illumination to the areas that would otherwise be deeply shadowed. By adding light to these darker areas, the fill light reveals details that would otherwise be lost and decreases the overall contrast ratio, which is the difference in brightness between the brightest and darkest parts of the subject. The fill light does not eliminate shadows entirely, but rather lifts them, making them less harsh and defined. The intensity of the fill light is generally lower than that of the key light, allowing for control over the desired level of shadow reduction. A weaker fill light results in higher contrast and a more dramatic look, while a stronger fill light leads to lower contrast and a softer, flatter appearance.