In article ,
harry writes:

Both tube and starter have sub-atmospheric gas filled glass bulbs. (Plus mercury in the tube) The common fault is for air to leak in.
The other fault is for a filiment in the tube to go open circuit.

The three most common failure modes for tubes at end of life a

1) Loss of the electron emission coating on the filament.

This was pretty much the only failure mode in all tubes until about
about 10 years ago. With switch-start control gear, it shows as a
blackened tube end which only glows orange and not white as the
starter repeatedly tries and fails to start the tube. No white is
because the filament is not emitting electrons when heated red-hot
(no thermionic emission), so there's no conduction into the gas-fill,
and the discharge can't start.
Electronic control gear detects this by seeing the tube start
to act as a rectifier and shuts down the tube to prevent it changing
to operate as a cold-cathode tube which has a number of dangers.

2) Run out of mercury in the gas.

Environmental regulations now require minimum mercury dosing of tubes
for the expected life (typically 1/10th of what older T12 tubes used).
Mercury is slowly absorbed into the electrodes and glass and lost from
the gas fill. This causes tubes to dim with age, and eventually to
run a dim pink when all the mercury has gone.

3) Phosphor worn out.

Tubes last much longer than they did and the phosphor efficiency drop
causes them to dim and become unviable.

Air doesn't leak into tubes, even ones which are very many decades old.

A fluorescent tube with electronic "choke" is as efficient as an LED bulb.

Not any more.
If you take into account losses in the fluorescent luminare (getting the
light from the wrong side of the tube to where you want it, or losing it),
they never were.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]