Hollow cathode effect

The hollow cathode effect allows electrical conduction at a lower voltage or with more current in a cold-cathode gas-discharge lamp when the cathode is a conductive tube open at one end than a similar lamp with a flat cathode. The hollow cathode effect was recognized by Friedrich Paschen in 1916.
In a hollow cathode, the electron emitting surface is in the inside of the tube. Several processes contribute to enhanced performance of a hollow cathode:
The hollow cathode effect is utilized in the electrodes for neon signs, in hollow-cathode lamps, and more.