How did the Edison effect lead to the development of vacuum tubes?

The Edison effect was a foundational discovery that paved the way for vacuum tube technology by revealing the principles of thermionic emission.

During the development of the incandescent lightbulb, Thomas Edison observed that an electric current could flow between a hot filament and a separate electrode inside the vacuum bulb, provided the electrode was positively charged. While Edison did not initially exploit this phenomenon, later scientific study—most notably by J.J. Thomson and John Ambrose Fleming—identified that this current was caused by the emission of electrons from the heated cathode.

This understanding directly enabled the creation of electron tubes:

• Rectification: Fleming utilized this effect to develop the thermionic valve, a two-electrode vacuum tube that could convert alternating current (AC) into direct current (DC), which was essential for early radio receivers.
• Amplification: In 1906, Lee De Forest advanced the technology by adding a third electrode (a grid) to the valve, creating the Audion. This allowed for the control and amplification of signals, facilitating the development of modern electronics, including telephony and early computers like ENIAC.123