A method comprises receiving (222,224,226,232,234,236) information identifying power on/off-related behavior (e.g. shutdown moment and/or elapsed time) from each of the plurality of lighting devices and partitioning the plurality of lighting devices in groups of lighting devices, e.g. Group1: L1+L2 and Group2: L3, based on the received information. Each of the groups comprises only lighting devices with similar power on/off-related behavior. The method further comprises controlling (242) the lighting device in response to a user command, determining that a problem has occurred when controlling the lighting device, and identifying the group that comprises the lighting device. The method also comprises determining a power on/off state of at least one other lighting device in the identified group, determining diagnostic information based the determined power on/off states, and providing (243) the diagnostic information to the user. The diagnostic information indicates a likely cause for the problem.