* Electron Excitation: The electrons in the beam have been accelerated to high speeds. When they collide with gas molecules (usually air) inside the tube, they transfer energy to the gas molecules. This excites the electrons within those gas molecules to higher energy levels.
* Photon Emission: The excited gas molecules are unstable and quickly return to their ground state, releasing the energy they absorbed as photons (light particles).
* Blue Light: The specific type of gas used in a Teltron tube, usually air, will emit photons in the blue range of the visible spectrum. This is why we see the blue glow.
So, it's not the electrons themselves that we see, but the light emitted by the excited gas molecules after being struck by the electron beam.
