The Lamp Room

12 years ago whilst at the LU station, I saw one of the T12 fixtures that had an EOL tube that basically was not doing the blinking/flashing but doing a 'plasma ball' effect with mercury migration and from what Dez mentioned that a lot of the T12 fixtures use SRS/QS ballasts - have I just seen a SRS/QS fixture with an EOL tube?

I can't imagine what you mean by plasma ball effect, but the old London Underground fittings were Quickstart or SRS and EOL tubes would just rectify, which resulted in mercury migration due to the one-way, half-wave-rectified conduction. Talking of the underground, I have fond memories from my early childhood (late 1960s) and the trains with the twin 5' 80W BC warm white tubes along the centre of the ceiling. They operated on a high frequency supply (several hundred Hertz?) so that the flickering of a rectifying tube was not visible. All I saw was light at one end of the tube which had disappeared by the centre due to the extreme mercury migration. I even remember standing on a seat to get a closer look.

That is amazing - I dream to get the SRS/QuickStart ballasts because they are magnetic ballasts with the starterless feature that is in the modern electronic ballasts that have a pre programmed start (but way way more snazzier) including the higher frequency

Can imagine the SRS/Quickstart being the more pricier compared to ordinary switchstart of the magnetic ballasted fixtures

SRS won't short out (starter blink) a tube with excessive high voltage across it (in one polarity - rectifying tube, or in both polarities - a tube EOL on both electrodes or a few other cases). So it can drive a tube further to EOL while it still lights

If the plasma ball effect involved blue light at one of the cathodes, that is the gear pushing power through a cathode which have no emitter left

Due to no emissive material, it can't form a low voltage drop discharge at the normal temperature the cathode is supposed to operate at - It is still too cold for bare Tungsten. At this point there are 2 possible outcomes :

- The tube will stay at a dim and flickery cold discharge state, at very low current

- The high voltage drop will lead to high power dissipation on the cathode, maybe to the point where it is once again becomes a hot cathode discharge (at the new high temperature). The high temperature will blow open the cathode and keep burning from the ends of the connection wires, as long as the discharge keeps conducting between them (and keeping the circuit closed as if the cathode was still there). The connection wires will burn back to the glass pinch, cracking it and letting air into the tube

It is not uncommon to see tubes with blown off phosphor in the ends on SRS. (The result of the air blowing into the tube)

That is amazing - I dream to get the SRS/QuickStart ballasts because they are magnetic ballasts with the starterless feature that is in the modern electronic ballasts that have a pre programmed start (but way way more snazzier) including the higher frequency

Can imagine the SRS/Quickstart being the more pricier compared to ordinary switchstart of the magnetic ballasted fixtures

You are aware I have SRS fittings listed on my trades list.....