After the invention of the light bulb,
Edison continued to experiment and
in 1883 found that he could detect
electrons flowing through the
vacuum from the lighted filament to
a metal plate mounted inside the
bulb. This discovery became known
as the Edison effect.
An English physicist, John
Fleming, took up where Edison left
off and found that the Edison effect
could also be used to detect radio
waves and convert them to electrical
signals. He went on to develop a
two-element vacuum tube called the
Fleming valve, later known as the
diode. Modern pn junction devices
are an outgrowth of this.