Described is a cartridge comprising a body adapted to contain a medicament, a bung slidably disposed in the body and having a distal face and a proximal face, and a light element coupled to a component of the cartridge. Further described is a medicament delivery device comprising the cartridge, a first receiver adapted to receive an optical signal from the light element and convert the optical signal into a first electrical signal, and a second receiver adapted to receive an optical signal from the light element and convert the optical signal into a second electrical signal.