A Soft box is a type of photographic lighting device, one of a number of photographic soft light devices. All the various soft light types create soft diffused light by directing light through some diffusing material, or by "bouncing" light off a second surface to diffuse the light. The best known form of bouncing source is the umbrella light where the light from the bulb is bounced off the inside of a metalized umbrella to create a soft indirect light.
A "soft box" is an enclosure around a bulb comprised of reflective side and back walls and a diffusing material at the front of the light.
The sides and back of the box are lined with a bright surface - an aluminized fabric surface or an aluminum foil, to act as an efficient reflector. In some commercially available models the diffuser is removable to allow the light to be used alone as a floodlight or with an umbrella reflector.
Soft boxes range in size from less than a foot square (30cm x 30cm)to huge soft boxes called lightbanks. One major manufacturer offers units where the illuminated diffusing surface is 15 x 40 feet (4.6m x 12.3m). These very large units are typically hung over large studio sets to provide broad, even, well controlled light. These lightbanks are best known as light sources for studio photography for the automotive industry.
Photographers choose soft box light sources for the soft even light they throw and for the even highlights they create. The quality of light closely resembles that of the light transmitted through a Shoji screen; the illumination comes from a (usually) evenly illuminated surface. Soft box lighting de-emphasizes lines and blemishes on the face of a human subject. Soft box lighting provide bright, even lighting, smooth broad highlight reflections in product photography, and gentle transitions from the illuminated areas to the areas of shadow. Reflections are of great importance when photographing shiny polished surfaces, reflective metal surfaces, and transparent materials like glass. The image of the highlight on such subjects is really a reflected image of the lightsource.
They are often easier to manage than umbrellas when it comes to controlling the amount of light that falls on the backdrop or background of an image. A softbox can be 'feathered', or aimed to direct stray light away from the background. "Barn doors" and "honeycomb grids" can also be used to restrict the area illuminated by soft boxes.
It can be used with either flash or continuous light sources such as fluorescent lamps or "hot lights" such as quartz halogen bulbs or tungsten bulbs. If soft box lights are used with 'hot' light sources, the user must be sure the softbox is heat rated for the wattage of the light it is attached to in order to avoid fire hazard.