A control system for controlling a plurality of lighting devices (13-16), comprising at least four lighting devices, and partitioning said plurality of lighting devices (13-16) into groups, said control system comprising: at least one input interface ; at least one output interface ; 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 (13-16), - partition said plurality of lighting devices (13-16) 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 (13-16) 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 ; 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 (13-16), - partition said plurality of lighting devices (13-16) 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 (13-16) 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 (13-16), - partition said plurality of lighting devices (13-16) 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 (13-16) 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. <EOS>