Using light to sculpt the subject requires a degree of directional light that skims and rakes across the subject to create form, shape and texture. This will be true when working with natural light or artificial lighting. In either case, the efforts of the photographer to create a directional light pattern also creates shadows. In that the photographer is responsible for creating or directing the light onto the subject, so too is the photographer responsible for handling the shadows that are created. In some cases, the shadows may be too strong or too deep that
additional (additive) light will be required to provide some degree of illumination of the shadow area.
In the studio environment, this task is usually handled by a “fill” light. With natural lighting, this job may be handled with a reflector, portable flash or some other light source. Where the main light is used to create the directional pattern of light on the subject, the fill lights job is to take care of the shadows. The illumination of the shadows by the fill light determines the lighting ratio of light on the subject.