The use of available light may pose a challenger. The brightness and direction of the light is often not adjustable, except perhaps for indoor lighting. This will limit the selection of shutter speeds, and may require the use of shades or reflectors to manipulate the light. It can also influence the time, location, and even orientation of the shooting to obtain the desired lighting conditions.
Levels of ambient light are most frequently considered relative to additional lighting used as fill light, in which case the ambient light is normally treated as the key light. In some cases, ambient light may be used as a fill, in which case additional lighting provides the stronger light source. The relative intensity of ambient light and fill light is known as the lighting ratio, an important factor in calculating contrast in the finished image.