An optical wireless communication system comprising a transmitter apparatus that comprises: an illumination light source configured to output visible light for illumination purposes, and a controller configured to control operation of the illumination light source to produce modulation of the visible light to provide an optical wireless communication signal representing data; a further light source configured to output further light, wherein the controller is configured to control operation of the further light source to produce modulation of the further light to provide a further optical wireless communication signal representing substantially the same data, wherein the visible light and the further light have different wavelengths.