Materials with light-controlled properties are extremely attractive for information technologies and, among the wide range of approaches, that of photorefractive media is particularly relevant(1,2). Photorefractivity is observed in photoconductors, where charge carriers photogenerated by nonuniform illumination redistribute over macroscopic distances, and where the resulting electric field modulates the refractive index. This effect has been used in a variety of devices for applications ranging from image treatment to beam steering and medical imaging. Compared with the more commonly studied inorganic crystals, photorefractive non-crystalline organic systems(3-6) offer a more technologically appealing alternative, as these materials are mechanically flexible, can be easily modified chemically and are inexpensive. Here we show how a photogenerated space - charge field can be used to control the switching between the two stable orientational states of ferroelectric liquid crystals. The resulting refractive-index patterns are stable, easily erasable and rewritable. In contrast to more traditional organic photorefractive materials, where the refractive index is continuously modulated by the applied field, the liquid-crystalline device described here is a 'binary' system, in which the refractive index n switches between two values (Delta n similar to 3 x 10(-2) in this case, but Delta n of the order of 10(-1) is, in principle, possible).