Hi all, I have a Philips 26w SOX-E lamp which I am trying to run with a Philips BSX26L81 ballast (we are on 230V here). First I tried running it with this ignitor:

Thorn  G53311 Ignitor (several years old)
- As the lamp starts to approach the end of run up it starts strobing and a plinking sound is heard. Not just flicker but actual strobing like a nightclub! Has anyone seen this before? Will it damage the lamp?
- After strobing for a minute or so it comes good and runs smoothly
- Lamp Voltage is 72V (data sheet specifies 69V I believe)

To try and get away from the strobing I tried a different one:

Parmar PB035K245 Ignitor (brand new)
- Run up is smooth
- Once the lamp has reached full brightness there is significant flicker, too much to put up with
- Lamp voltage is 78V, is this causing the flicker?

I can't understand how an igniter can change the run voltage of the lamp! Shouldn't it be out of circuit once the lamp has run up? I'm not sure what the next move should be. Perhaps I should try to obtain the recommended Philips SX26 ignitor?  Any help or advice would be appreciated.

It seems the lamp has difficulties to hold the arc, better to say reignite after the current zero cross (bad electrode, gas cleanup, bad ballast). The igniter may then act and help it to reignite, hence the varying behavior on different ignitors.
So you may check the arc current. If it is correct (or a bit lower), the ballast is likely good.
Then keep the lamp burning for a few hour UNINTERRUPTED, there is high chance it will recover. Just monitor tge ballast temperature, if it does not start to overheat severely.

We use a little fan that we can sit on top of a ballast that runs hot to give it the necessary cooling and keep the temperature to within operating limits. 

Funny enough, linear sodium lamps do the same, even on their original autoleaks!, my 140 watt flickers wildly just as it reaches full run up!
Could just be the ignitor and ballast are not compatible?

Are LPS bulbs still being produced?

Are LPS bulbs still being produced?

Unfortunately not, the Philips Hamilton plant that made SOX lamps closed down in August 2019. 

Oh that stinks. Wonder why they stopped production

Medved that makes sense. I forgot to mention this is a new lamp with less than 10hrs on it. I have only run it twice for a few hours each time.

Angryhorse that is interesting, I thought an autoleak ballast might be a solution to the problem...

Oh that stinks. Wonder why they stopped production

Lack of demand since the takeover of LED. Simple as that 

A 26W SOX-E lamp should run perfectly on standard 35W SOX gear, either a leak transformer or choke/ignitor. The recommended ignitor is the Philips SX26, but they are rather thin on the ground. Any 2-wire ignitor for a 35W lamp should work ok, though. 26W ballasts do exist, but they're as rare as hen's teeth 

Led is killed off a lot of Hid and fluorescent fixtures.
And Wal-Mart has quit selling fluorescent bulbs in there stores in favor of Led. I see led as a disease.

Medved that makes sense. I forgot to mention this is a new lamp with less than 10hrs on it. I have only run it twice for a few hours each time.

Angryhorse that is interesting, I thought an autoleak ballast might be a solution to the problem...

Hard to tell anymore!, my 140watt SLI/H is on its genuine, Thorn G 53232.4 auto leak, but just at the point the discharge levels out, it starts to flicker wildly, with that same fluttering noise you describe!, but with the SLI, this could be just down to its discharge tube shape?

Hard to tell anymore!, my 140watt SLI/H is on its genuine, Thorn G 53232.4 auto leak, but just at the point the discharge levels out, it starts to flicker wildly, with that same fluttering noise you describe!, but with the SLI, this could be just down to its discharge tube shape?

That's interesting. My 140WSLI/H runs on a Philips L5090BX and although it flickers at start-up, it soon settles down and there is no noise 

One of the phenomena of the low pressure sodium lamps is that during run-up, its voltage first peaks and then decreases.  This is because discharge voltage is higher in a sodium-neon mixture than in either pure neon or pure sodium.  If the ballast OCV is lower than required to keep the lamp running, then it may extinguish just before reaching full regime.  Different ignitor types may be successful in keeping the lamp running while it passes through this most difficult phase of run-up.  In a lamp that is slightly impure, the RMS voltage may not be especially high but the reignition voltage on each half-cycle could approach or exceed what the control gear can deliver at that instant and then some instability might be observed.

One of the phenomena of the low pressure sodium lamps is that during run-up, its voltage first peaks and then decreases.  This is because discharge voltage is higher in a sodium-neon mixture than in either pure neon or pure sodium.  If the ballast OCV is lower than required to keep the lamp running, then it may extinguish just before reaching full regime.  Different ignitor types may be successful in keeping the lamp running while it passes through this most difficult phase of run-up.  In a lamp that is slightly impure, the RMS voltage may not be especially high but the reignition voltage on each half-cycle could approach or exceed what the control gear can deliver at that instant and then some instability might be observed.

This also explains the phenomena behind the wattage rise and fall I see during warm up when using Fulham ballasts for my SOX lamps.

James yes I noticed on the Philips datasheet that the voltage rises and then falls again. As you guessed he strobing happens during the reigon of peak lamp voltage on the chart.

When I look at the voltage on my RMS multimeter I think why at 78v on a 230v supply it won't maintain the discharge but perhaps the RMS voltage value is not giving a true indication of what's going on at the zero crossing re-ignition event...