In article ,
Ian Stirling writes:

You get the best life from a bulb if you turn the heater filliments on
some 1-2 seconds before actually starting the light.
If you don't, then the heaters get bombarded with ions and this dislodges
lots of their substance, which ends up on the walls of the tube.
With a tube that's working properly, the heater emits electrons, which
neutralise the ions before they get to the fillimnent.

The actual bit of the heater which does the work is in fact heated a bit
by the incoming ions reacting with nearby electrons, so runs a bit hotter
than due to the current alone.

Yes. Once the arc is established, supplementary cathode heating is not
required. (However, it does increase the cathode life slightly, but uses
more energy too.)

Similarly with CCFLs, the unheated cathode actually gets hot, which does
similar things.

Cold Cathode fluorescents don't rely on the cathode getting hot.
It would have to get to bright orange temperature before it started
becoming a thermionic emitter. They just operate with a higher cathode
fall voltage to get the electrons out of the metal (which is less
efficient than the conventional thermionic cathode tubes).
This also disloges the cathode material, but the electrodes are normally
formed from the inside of a cylinder, which means most of the disloged
material ends up sticking to some other part of the cathode and it doesn't
wear out very fast. The electric field inside a cylindrical electrode
doesn't increase as much, which also prevents the ions and electrons
picking up large energy just before they impact the surface. CCFLs
normally have a much longer life than conventional fluorescents because
of this. (The tiny ones used in scanners have much simpler cathodes
and a much shorter life.)

Both of these are a reason why dimming some fluorescant tubes may cause
blackening at the ends of the tubes and premature failure.

Circuitry designed for dimming fluorescents will provide supplementary
cathode heating at reduced arc current to ensure the cathode stays at
thermionic operating temperature. (Mostly dimming ballasts provide the
supplementary heating continuously regardless of the arc current.)

--
Andrew Gabriel