A system comprising: an arrangement of contiguously-mounted lighting units arranged to emit light comprising visible illumination into an environment; transmission circuitry arranged to temporally modulate the visible illumination emitted by each of some or all of the arrangement of lighting units so as to embed a different respective signal into the visible illumination emitted by a data-transmitting luminous area of each, thereby providing multiple data-transmitting lighting units; and detecting equipment comprising a camera for capturing images of the data-transmitting luminous areas of one or more of said data-transmitting lighting units, and an image processing module configured to detect the respective signals based on one or more of the captured images; wherein the system is further configured to spatially modulate at least part of the light emitted by each of one, some or all of the lighting units of said arrangement with a spatial pattern, thereby providing one or more spatially-patterned lighting units; wherein the image processing module of the detecting equipment is configured to distinguish each of said one or more data-transmitting lighting units from amongst the multiple data-transmitting lighting units, and thereby detect the respective signals embedded in the illumination from said one or more data-transmitting lighting units, characterised in that the distinguishing each of said one or more data-transmitting lighting units from amongst the multiple data-transmitting lighting units is based on an auto correlation of said spatial pattern emitted by said one or more spatially-patterned lighting units appearing in one or more of the captured images. an arrangement of contiguously-mounted lighting units arranged to emit light comprising visible illumination into an environment; transmission circuitry arranged to temporally modulate the visible illumination emitted by each of some or all of the arrangement of lighting units so as to embed a different respective signal into the visible illumination emitted by a data-transmitting luminous area of each, thereby providing multiple data-transmitting lighting units; and detecting equipment comprising a camera for capturing images of the data-transmitting luminous areas of one or more of said data-transmitting lighting units, and an image processing module configured to detect the respective signals based on one or more of the captured images; wherein the system is further configured to spatially modulate at least part of the light emitted by each of one, some or all of the lighting units of said arrangement with a spatial pattern, thereby providing one or more spatially-patterned lighting units; wherein the image processing module of the detecting equipment is configured to distinguish each of said one or more data-transmitting lighting units from amongst the multiple data-transmitting lighting units, and thereby detect the respective signals embedded in the illumination from said one or more data-transmitting lighting units, characterised in that the distinguishing each of said one or more data-transmitting lighting units from amongst the multiple data-transmitting lighting units is based on an auto correlation of said spatial pattern emitted by said one or more spatially-patterned lighting units appearing in one or more of the captured images.