A system of replaceable components comprising a plurality of components connected in a wireless network under a collective ID, and at least one unconnected component available to join the network; wherein the components are divided amongst a plurality of luminaires , each respective one of the luminaires comprising a respective subgroup of the components (12a-12d) including at least one lamp, and each of the subgroups having an individual respective subgroup ID identifying the respective subgroup; and wherein at least a first one of the components is configured to automatically: - detect whether a previously-present one of said components from the same respective one of said subgroups as the first component is missing from the network; and - in response to the detection that the previously-present component is missing from the network, cause the unconnected component to be joined to the wireless network under said collective ID, and to be assigned to the same respective subgroup as the first component under the same respective subgroup ID; wherein the first component is one of said plurality of components already connected in the network and the first component is further configured to: - detect that the unconnected component is available to join the network, - perform said causing of the unconnected component to join the network in response to the detection both that the new component is available to join the network and that the previously present component is missing from the network and - detect whether the new component is estimated to be within a predefined spatial proximity of the first component by checking whether a signal is received from the new component via a constrained signaling channel whereby propagation of the signal is limited by a physical property of the luminaire, wherein if the signal is received the new component is determined to be within said spatial proximity; wherein the constrained signalling channel is via coded light, ultrasound and/or radio, and said physical property of the respective luminaire comprises at least part of a housing of the luminaire which at least partially blocks the propagation of the light, radio or ultrasound signal, the signaling channel thereby being constrained and at least said assigning of the new component to the respective subgroup is performed on condition of detecting that the new component is estimated to be within said spatial proximity. - detect whether a previously-present one of said components from the same respective one of said subgroups as the first component is missing from the network; and - in response to the detection that the previously-present component is missing from the network, cause the unconnected component to be joined to the wireless network under said collective ID, and to be assigned to the same respective subgroup as the first component under the same respective subgroup ID; - detect that the unconnected component is available to join the network, - perform said causing of the unconnected component to join the network in response to the detection both that the new component is available to join the network and that the previously present component is missing from the network and - detect whether the new component is estimated to be within a predefined spatial proximity of the first component by checking whether a signal is received from the new component via a constrained signaling channel whereby propagation of the signal is limited by a physical property of the luminaire, wherein if the signal is received the new component is determined to be within said spatial proximity; <EOS>