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.
[1] The hollow cathode effect was recognized by Friedrich Paschen in 1916.
[2] 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.
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