 Since the electrons emitted within an image dissector are collected by the electron multiplier or anode only during the very brief time an area of the "electron image" is exposed, the bulk of the electrons are lost.Thus the earliest image dissectors were very inefficient, and extremely bright illumination was required for it to be used effectively.Farnsworth addressed this problem with the invention of an "electron multiplier" (not to be confused with contemporary electron multipliers), a device that increased the number of electrons in a circuit by generating "secondary emissions" of electrons from a pair of opposed surfaces, thus amplifying the electrical signal.