Arc swirl on a SON lamp!!, is that even possible?

[AngryHorse]

Ok, bear with me here!, my GE 50watt SON-T has stopped flickering now, and started arc swirling!
I`ve only ever seen this in halide lamps running vertical, where the arc leaves the electrode tip, with a slight bow, (vertical running don`t forget), then wanders around the tube causing a swirling motion reflected on the wall next to the light.

My GE in its coach light, puts a rectangle lit shape, as it shines through the window on my bedroom ceiling, and if you watch this shape carefully, what seems like a flicker at first glance, is a definite shadow that goes back and forth within the rectangle!

The only thing I can put this down to is arc swirl!, but I`ve NEVER seen this in a SON lamp before, (with the arc being very constricted within the confines of the narrow tube), your thoughts?????

[Kev]

One for James!

[James]

For sure it can swirl in the vicinity of the electrodes due to the arc root wandering around the tip, but on 50Hz is should never swirl in the main body of the arc tube. The arc in SON lamps is wall-stabilised, ie the shape of the arctube wall is what determines the arc shape (whereas in MB and MBI lamps the arc is constricted and the wall doesn't influence the arc).

On HF however, SON lamps can do strange things because the flat ends of the arc tube make good sound reflectors, and acoustic waves at certain frequencies can set up resonances that cause the arc to snake around. Electronic ballasts for SON have to be made to avoid frequencies known to cause such problems.

[AngryHorse]

That would be interesting to watch!
So a similar thing can happen, as in the MBF arc, whereas the root of the arc sits half on the electrode tip, and half on the overwinds, with the half on the overwinds moving around them, causing the same flickering effect.

Thats interesting as I have watched many a SON arc through a dark glass, but never seen one do this before.

[Liam]

That's what happened to my SLI a couple of month back it started going dim then flickering then going back to normal, after a week or so i noticed the arc swirling around one of the electrodes until a few week later and now its gone EOL and cycles like mad. Has it slightly pinked out? And how is it on start up?

Any chance of getting a picture of it mate?

[AngryHorse]

Start and running is as normal, so I don`t think its at EOL?, it also wasn`t doing it this morning.

[Liam]

That's mine did, it started off flickering for around 30 mins to a couple of hours then stopped, but got worse as the weeks went passed until it started cycling.