It is a photographic lightening device that is used to create a soft and diffused light. The design of a soft box is such that it is an enclosure around the light source, has sides for reflecting, back walls and diffusing material in front of source. The make the reflecting efficient sides and back walls are made of bright surface –either they are aluminized or covered with aluminum foil. So it does not matter if your light source is flash or continuous like florescent bulb. But keep in mind that to bear the wattage of heat of light it must be heat rated.