This paper introduces an input and output device that enables illumination, bi-directional data communication, and position sensing on a soft cloth. This "LightCloth" is woven from diffusive optical fibers. Since the fibers are arranged in parallel, the cloth has one-dimensional position information. Sensor-emitter pairs attached to bundles of contiguous fibers enable bundle-specific light input and output. We developed a prototype system that allows full-color illumination and 8-bit data input by infrared signals. We present as an application a chair with a Light-Cloth cover whose illumination pattern is specified using an infrared light pen. Here we describe the implementation details of the device and discuss possible interactions using the device.