The invention introduces the concept of priorities into DALI technology. A switchgear (18) used to this end comprises two inputs (28, 22) to which a DALI bus (40, 38) can respectively be connected, and an output (24) to which another DALI bus (26) can be connected. A data processing unit (56) allocates priorities to the signals entering via the two inputs (28, 22) according to pre-determined criteria, and supplies the signals to the output according to their priority, through which they are then forwarded to electronic ballasts (14). The switchgear (18), especially the data processing unit (56), decides which instruction is carried out by means of the priority assignment in the event of collision conflicts between different instructions, for example central building control instructions and local control instructions.