Devices (10) comprise target detectors (11) for detecting presences of targets in first areas (1) and transmitters (12) for in response to detected presences transmitting multicast messages to controllers (20) and lamps (21-24) in wireless networked lighting systems. Such multicast messages increase reliabilities of the systems. The multicast messages switch on the lamps (21-24). Preferably, the multicast messages are only transmitted in case relatively small amounts of light are detected in second areas (2). In case relatively large amounts of light are detected in the second areas (2), unicast messages are in response to detected presences transmitted from the devices (10) to the controllers (20) that in response control the lamps (21-24) to be switched on. The first and second areas (1, 2) may be at least partly overlapping areas. The devices (10) may comprise internal light detectors (13) for detecting the amounts of light in the second areas (2) or receivers for receiving light detection information from external light detectors.