A computer-implemented method is provided, in which a plurality of luminance change frequencies of a light emitter is determined by coding one of a plurality of transmission information sources. The light emitter transmits a transmission information source by a change in luminance according to each of the plurality of luminance change frequencies. A signal, which controls the change in luminance of the light emitter according to each of the plurality of luminance change frequencies, is output to the light emitter. The plurality of luminance change frequencies include a first frequency and a second frequency. A signal of the first frequency and a signal of the second frequency respectively cause the light emitter to change in luminance according to the first frequency during a first time period and to change in luminance according to the second frequency during a second time period after the first time period has elapsed.