A method of configuring a plurality of installed lighting units (110) comprises determining that a first installed lighting unit (110) should remain a member of a first logical group, and that a second installed lighting unit (110) should switch to a second logical group. The method further comprises interrupting a supply of electric power to the first installed lighting unit (110), e.g. via a suitable an interrupter (310), whereby the first installed lighting unit (110) is incapable of receiving a command from a controller of at least the first and second installed lighting units. The method further comprises broadcasting, from the controller, to at least the first and second installed lighting units (110), a command arranged to cause any suitable lighting unit (110) which receives it to join the second logical group, thereby causing the second installed lighting unit (110) to switch to the second logical group. The method further comprises resuming the supply of electric power to the first installed lighting unit (110) whereby it becomes operable to receive and react to commands from the controller.