The Lamp Room

Anyone else had this?
I've been converting a bulkhead to run 35W SOX in the last few days and used a Philips BSX 355 L82 35/55W magnetic ballast paired with a Parmar PB035K245 ignitor.

While testing it I've found some lamps seem to flicker quite strongly once fully warmed up, it is quite noticeable and can be seen in the are illuminated by the lamp as well as when looking directly at it.
Interestingly when the ignitor is taken out the circuit while live, the flickering reduced down to what you'd expect for a lamp driven on 50Hz mains. There is also a noticeable change in the sound of the ballast when the ignitor is removed from the circuit.
I have also tried various Thorn and Philips ignitors and other lamps with varying results, some seem to work ok while others still flicker.

Will the flicker just go away on its own if run for long enough or is there more at play here? I'm sure it is not rectifying, there is no "angry" buzz from the ballast and the flicker is not like that of a rectifying fluorescent lamp (and in fact is almost akin to the shimmering of a cold T8 lamp on mag gear), and the lamps are not EOL or close to it.

I have seen the same with SON lamps. Basically, the ignitor firing voltage is a bit low or the overshoot filtering is missing, so the ignitor starts working hen the lamp is lit

This will usually happen at borderline high arc voltages, so if the lamp is new or a bit colder it won't happen

The ignitor momentarily loads the ballast output causing a voltage drop, therefore the flicker

If left for long the flicker may go on and off in cycles, as the lamp power is reduced during the flickering, it cools down and the arc voltage drops below what triggers the ignitor

SOX may have less pronounced relation between arc V and temperature, but i think they may have enough of it for the same effect to happen

Thanks Ash, that sounds most likely what is happening as it is only doing it once the lamp has fully warmed up. Also the Helium contaminated lamp I have did not do it either, and that had settles on a lower arc voltage when fully warmed up than the other lamps did.

This is the fitting I am now attempting to repair the Thorn ignitor for as apart from the pre-existing issue with that it does not cause the flicker when the lamp is at full power.