Vacuum versus gas-filled

There are 2 kinds of tubes:

-Vacuum tubes 

-Gas-filled tubes.

Vacuum tubes are very more common.Vacuum tubes permit electrons to be accelerated to high speeds, resulting in a large current. This current can be made more or less intense, or which is focused into a beam and guided in a specific direction. The intensity and beam direction can be changed with extreme rapidity, making possible variety of different useful effects.

Gas filled tubes have constant voltage drop, no matter what current is. This makes them useful as voltage regulators for high voltage, high current power supplies. Gas filled tubes can withstand conditions which would destroy the semiconductor regulating devices. Gas filled tubes fluoresce, or emit infrared, visible light and ultraviolet at defined wavelengths. This property can be put to use for the decorative lighting. Neon signs are gas filled electron tubes.

In any electron tube, charge carriers are free electrons. This means that electrons are not bound to atoms, but instead, fly through space in the barrage, like photons of visible light, or like atomic nuclei in the particle accelerator.