A lighting network comprising: - a controller for controlling a plurality of lighting units, wherein the controller is operable to broadcast a first command, the first command being arranged to cause any suitable lighting unit which receives it to join a first logical group, wherein the controller is further operable to broadcast a second command, the second command being arranged to cause any suitable lighting unit which receives it to join a second logical group; - one or more lighting fixtures comprising an installed lighting unit and an interrupter, wherein the one or more lighting fixture is connected to the controller so as to be able to receive one or more commands therefrom; wherein the interrupter is suitable for interrupting a supply of electric power to the installed lighting unit whereby it is incapable of receiving said one or more commands from the controller; wherein the lighting network comprises at least a first installed lighting unit that should remain a member of a first logical group, and a second installed lighting unit that should switch to a second logical group in response to receiving said second command; wherein the controller is configured to broadcast the second command to at least the first installed lighting unit and the second installed lighting unit, while the interrupter of the first installed lighting unit interrupts a supply of electric power to the first installed lighting unit such that the first installed lighting unit is inacapable of receiving the second command, thereby causing the second installed lighting unit to switch to the second logical group. - a controller for controlling a plurality of lighting units, wherein the controller is operable to broadcast a first command, the first command being arranged to cause any suitable lighting unit which receives it to join a first logical group, wherein the controller is further operable to broadcast a second command, the second command being arranged to cause any suitable lighting unit which receives it to join a second logical group; wherein the controller is operable to broadcast a first command, the first command being arranged to cause any suitable lighting unit which receives it to join a first logical group, wherein the controller is further operable to broadcast a second command, the second command being arranged to cause any suitable lighting unit which receives it to join a second logical group; - one or more lighting fixtures comprising an installed lighting unit and an interrupter, wherein the one or more lighting fixture is connected to the controller so as to be able to receive one or more commands therefrom; wherein the interrupter is suitable for interrupting a supply of electric power to the installed lighting unit whereby it is incapable of receiving said one or more commands from the controller; wherein the lighting network comprises at least a first installed lighting unit that should remain a member of a first logical group, and a second installed lighting unit that should switch to a second logical group in response to receiving said second command; wherein the controller is configured to broadcast the second command to at least the first installed lighting unit and the second installed lighting unit, while the interrupter of the first installed lighting unit interrupts a supply of electric power to the first installed lighting unit such that the first installed lighting unit is inacapable of receiving the second command, thereby causing the second installed lighting unit to switch to the second logical group. wherein the interrupter is suitable for interrupting a supply of electric power to the installed lighting unit whereby it is incapable of receiving said one or more commands from the controller; wherein the lighting network comprises at least a first installed lighting unit that should remain a member of a first logical group, and a second installed lighting unit that should switch to a second logical group in response to receiving said second command; wherein the controller is configured to broadcast the second command to at least the first installed lighting unit and the second installed lighting unit, while the interrupter of the first installed lighting unit interrupts a supply of electric power to the first installed lighting unit such that the first installed lighting unit is inacapable of receiving the second command, thereby causing the second installed lighting unit to switch to the second logical group.