Fill-in Flash; Fill-in Light; Fill; Fill Light
The term ‘fill-in’ or ‘fill’ is used in photography to indicate the use of additional lighting to brighten shadow areas or darker areas in a scene. Fill-in Flash; Fill-in Light; Fill light – are expressions used to describe the use of secondary lights to lift locally dark areas of shadow in a scene.
In very bright light, under a key light, or direct sunlight the range of contrast from black to white is very wide. This contrast is often too wide for the digital image sensor to resolve. Dark areas become black and lose detail. ‘Fill-in’ light is used to brighten the darker areas so the camera can capture the detail that would have been lost in pure black.
Fill can be used to soften the shadows from a main hard light, or to brighten enough for the dark area to be clearly visible on the picture.
The fill light must be of a lower intensity than the main light or it would make the shot look unbalanced or unnatural. However, reflectors, remote light sources and even hand-held torches will all provide a source to brighten shadows.
Different types of fill
Almost any type of light or reflector can be used to lift shadows in a scene. Usually, a photographic light of some kind is used for Fill. The options include, pop-up flash, off-camera flash, studio strobe, soft boxes or other lighting. When using flash or studio strobes the term applied is Fill-in Flash. The use of always-on or continuous lights or diffusers requires the use of the term Fill-in Light.
Overall, it is the context of the scene that is important when choosing a light for fill. Consider a dim, 1950’s living room scene. In this shadowy, atmospheric scene you might use tungsten bulb type lights to create a colour cast (yellow light), but also lift shadows slightly in some areas of the scene. Any light, not just photographic lights can therefore be used.