A control system for controlling a plurality of lighting devices, comprising at least four lighting devices, and partitioning said plurality of lighting devices into groups, said control system comprising: at least one input interface; at least one output interface (4,9); and at least one processor configured to: - use said at least one input interface to receive information identifying power on/off-related behavior from each of said plurality of lighting devices, - partition said plurality of lighting devices in groups of at least two lighting devices based on said received information, each of said groups comprising only lighting devices with similar power on/off-related behavior, - use said at least one output interface to control a lighting device of said plurality of lighting devices in response to a user command, - determine whether a problem has occurred when controlling said lighting device, - identify one group of said groups, said one group comprising said lighting device, - determine a power on/off state of at least one other lighting device in said identified group, - determine diagnostic information based on said determined power on/off states, said diagnostic information indicating a likely cause for said problem, and - use said at least one output interface to provide said diagnostic information to said user. at least one input interface; at least one output interface (4,9); and at least one processor configured to: - use said at least one input interface to receive information identifying power on/off-related behavior from each of said plurality of lighting devices, - partition said plurality of lighting devices in groups of at least two lighting devices based on said received information, each of said groups comprising only lighting devices with similar power on/off-related behavior, - use said at least one output interface to control a lighting device of said plurality of lighting devices in response to a user command, - determine whether a problem has occurred when controlling said lighting device, - identify one group of said groups, said one group comprising said lighting device, - determine a power on/off state of at least one other lighting device in said identified group, - determine diagnostic information based on said determined power on/off states, said diagnostic information indicating a likely cause for said problem, and - use said at least one output interface to provide said diagnostic information to said user. - use said at least one input interface to receive information identifying power on/off-related behavior from each of said plurality of lighting devices, - partition said plurality of lighting devices in groups of at least two lighting devices based on said received information, each of said groups comprising only lighting devices with similar power on/off-related behavior, - use said at least one output interface to control a lighting device of said plurality of lighting devices in response to a user command, - determine whether a problem has occurred when controlling said lighting device, - identify one group of said groups, said one group comprising said lighting device, - determine a power on/off state of at least one other lighting device in said identified group, - determine diagnostic information based on said determined power on/off states, said diagnostic information indicating a likely cause for said problem, and - use said at least one output interface to provide said diagnostic information to said user.