An optical wireless communication device comprising: a receiver comprising: a dual-wavelength filter configured to filter light arriving at the receiver, wherein the dual-wavelength filter is configured to pass light of a first frequency and light of a second, different frequency, and wherein the dual-wavelength filter is configured to substantially block light of a third frequency between the first frequency and second frequency; and a photodetector configured to receive the filtered light and to sense modulated light of the first frequency and/or modulated light of the second frequency to produce at least one receiver signal; demodulation circuitry and a processing resource for performing a demodulation and processing with respect to the at least one receiver signal to obtain data encoded in the modulated light of the first frequency and/or data encoded in the modulated light of the second frequency; a transmitter comprising a light source configured to output modulated light of the third frequency; a further transmitter comprising a further light source configured to output modulated light of the second frequency; and a controller configured to control operation of the transmitter and further transmitter to produce an output OWC signal in which data is encoded by modulation of light emitted by the light source and/or further light source, wherein the controller is further configured to select a first mode of operation or second mode of operation for the OWC device, wherein: the first mode of operation comprises receiving modulated light of the first frequency and/or second frequency and transmitting data by modulation of light of the third frequency emitted by the transmitter; and the second mode of operation comprises receiving modulated light of the second frequency and transmitting data by modulation of light of the second frequency emitted by the further transmitter. a receiver comprising: a dual-wavelength filter configured to filter light arriving at the receiver, wherein the dual-wavelength filter is configured to pass light of a first frequency and light of a second, different frequency, and wherein the dual-wavelength filter is configured to substantially block light of a third frequency between the first frequency and second frequency; and a photodetector configured to receive the filtered light and to sense modulated light of the first frequency and/or modulated light of the second frequency to produce at least one receiver signal; a dual-wavelength filter configured to filter light arriving at the receiver, wherein the dual-wavelength filter is configured to pass light of a first frequency and light of a second, different frequency, and wherein the dual-wavelength filter is configured to substantially block light of a third frequency between the first frequency and second frequency; and a photodetector configured to receive the filtered light and to sense modulated light of the first frequency and/or modulated light of the second frequency to produce at least one receiver signal; demodulation circuitry and a processing resource for performing a demodulation and processing with respect to the at least one receiver signal to obtain data encoded in the modulated light of the first frequency and/or data encoded in the modulated light of the second frequency; a transmitter comprising a light source configured to output modulated light of the third frequency; a further transmitter comprising a further light source configured to output modulated light of the second frequency; and a controller configured to control operation of the transmitter and further transmitter to produce an output OWC signal in which data is encoded by modulation of light emitted by the light source and/or further light source, wherein the controller is further configured to select a first mode of operation or second mode of operation for the OWC device, wherein: the first mode of operation comprises receiving modulated light of the first frequency and/or second frequency and transmitting data by modulation of light of the third frequency emitted by the transmitter; and the second mode of operation comprises receiving modulated light of the second frequency and transmitting data by modulation of light of the second frequency emitted by the further transmitter.