A light branching section applies a light pulse emitted in synchronism with a drive pulse, to an optical fiber line path, and receives the light returning from the line path. Characteristics of the smoking articles may be changed to increase the delivery of smoke constituents in the first few puffs in order to maintain a constant ISO NFDPM yield. The processor is connected to a driver on primary side through at least one coupling element and to the electronic switch. Corresponding apparatus and a computer program are also provided.