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 Post subject: Re: SOX lamps
PostPosted: Fri Jan 25, 2013 11:21 pm 
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Hi, Can someone with a bit of technical knowledge answer a question for me?

I have a lamp (Philips MA-not sure which), which has a large ballast marked 135/180 watt SOX, however these lamps have been used with 91 watt SOX-E bulbs, as there was one in it when I got it. Will running a 91 watt SOX-E with this gear shorten the life of the lamp or ballast, or will it be OK to use it without it doing any noticeable shortening of the life of the lamp?


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 Post subject: Re: SOX lamps
PostPosted: Sat Jan 26, 2013 7:53 am 
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Your MA is either a MA50 for 135W SOX or a MA60 for 180W SOX. They both used the same gear. A 180W SOX lamp is almost 4ft/1200mm long, so if that measurement is too big for the fitting, you have a MA50.

The 91W SOX E lamp is a low energy version of the standard 135W lamp (which means you probably have a MA50). However this and all SOX E lamps achieve the lower rating by a combination of better thermal insulation (which reduces heat loss) and gear which runs the lamp at a lower current (but a higher voltage) than a conventional lamp.

If a SOX-E lamp is run on conventional gear, the circuit rating is the same as a normal lamp - the revised gear is needed to achieve the power savings.

So you can run your lamp on the gear that is fitted, it will run at 135W, but you won't shorten the lamp/gear life.


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 Post subject: Re: SOX lamps
PostPosted: Sat Jan 26, 2013 1:17 pm 
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Thankyou for that info. The lamp is a MA50, as it states 135W SOX on a label inside the fitting. That is the only bit readable on the label, the rest has worn off. I will try the lamp soon and see if it actually works!


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 Post subject: Re: SOX lamps
PostPosted: Sat Jul 19, 2014 8:54 pm 
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It amused me how Southampton liked to purchase SOX-E lamps for its street lighting rather than SOX lamps like in Hampshire. You would end up seeing something like a Phosco P125 fitted with a 36W SOX-E lamp running on a 60/85W SOI leak transformer. It's as if nobody told the council that to realise power savings you needed a modern compatible ballast.


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 Post subject: Re: SOX lamps
PostPosted: Sun Sep 14, 2014 7:00 pm 
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I'm trying to gauge some idea of the lifetime remaining in some used 55W SOX lamps.

How good an indicator is measuring the running voltage?

At what point should it have reached a steady value? Say, 30min after switch on?

Any other pointers as to good 'rule-of-thumb' ideas?

Thanks

Adrian


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 Post subject: Re: SOX lamps
PostPosted: Mon Sep 15, 2014 6:03 pm 
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Voltage slowly rises as the lamp age. New lamps have lower running voltages than old ones.

Steady state voltage is reached when the sodium discharge is at full power.

The usual failure is lack of emmissive material on the electrodes. So if there is lots of sputter on the inside of the glass then the lamp will last not as long as one without.

Failure modes that can't be predicted are loss of vacuum from the outer tube or the arc tube leaking into the outer tube as the seals around the lead in wires fail.

Black ends of the arc tube are not an indication of failure - new lamps come like this.


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 Post subject: Re: SOX lamps
PostPosted: Sat Dec 13, 2014 10:54 pm 
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Hi All,

I have a question about the colour of SOX lamps when they first switch on. I apologise if this  question has been asked before.

I have two Philips 135W lamps, I think they are about 2013 and 2014. One switches on with what I call the perfect colour (Quote from Miranda Hart) , yellow at the electrode end and a lovely red/purple colour in the tube. The other lamp switches on and is vibrant red all over with no yellow at the electrode end!

Why is this?

They both came from lanterns that were  in service, the all over red one is a year older than the Perfect one?

Regards,

Andrew.


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 Post subject: Re: SOX lamps
PostPosted: Sun Dec 14, 2014 9:09 am 
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The difference between pink/purple and deep red is due to the amount of argon/neon in the tube. More neon means more red.

The tube that has a yellow end has some sodium near/or on the electrodes which as they are the hottest part, allows it to vapourise at switch on as the emissive material on the electrodes heats up,  producing the yellow colour.

The other tube has the sodium in the cooler parts of the arc tube so until it warms up, it remains red.


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 Post subject: Re: SOX lamps
PostPosted: Sun Dec 14, 2014 7:46 pm 
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Thanks phosco152 for the info. The first tube I tried only the electrodes glowed.

I have seen lanterns running red all night. What would cause this?

Regards,

Andrew.


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 Post subject: Re: SOX lamps
PostPosted: Mon Dec 15, 2014 12:43 am 
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meppso wrote:
I have seen lanterns running red all night. What would cause this?


Low pressure sodium lamps have always been at the more interesting end of the spectrum (excuse the pun) and in some respects could be regarded as living chemistry demonstration. Their method of operation is simple and the resulting electrical and physical changes as the lamp warms up can be viewed perfectly over several minutes, until the lamp has reached full output.

The history and development of the low pressure lamp has been recorded elsewhere including some excellent websites, so I needn't duplicate it here. Others may be able to explain this better than me in any case!

However, your observation of some lanterns running red all night is valid one and is something everyone here will have come across too.

Without waffling too much, the reason for the red glow is down to one thing - a loss of vacuum. If you are fortunate enough to check out a SOX lamp, it comes in two main sections - a sealed glass "U" tube which contains the metallic sodium, some neon and argon gas and two electrodes which are connected to the lamp cap. There is also a larger outer glass vacuum bulb or "envelope" which is coated on the inside surface with an infra-red reflective coating to provide thermal insulation. Even without the envelope, the bare lamp could be plugged into the lantern and it would glow the characteristic red colour you have described. However, it would struggle to go much further than this because without the outer envelope and its vacuum, the heat from the discharge would be lost and the sodium wouldn't get hot enough for the lamp to run up properly (as I discovered to my cost after dropping my first ever 35W lamp).

When a SOX lantern is exhibiting the behaviour you describe, it will be found that the vacuum in the outer envelope will have been lost, usually down to a failure of the main seal or an actual crack in the glass envelope. The only option is to replace the lamp.

Whilst a marvel of technology, the vulnerable vacuum of a SOX lamp can be its Achillies heel, as it can be compromised by vibration, impacts and even the quality of the lamp itself. Interestingly, the loss of vacuum won't turn a lamp red straightaway, unless its loss is very dramatic. You will often see early signs of this condition in that the lamp won't quite run up to full or you'll see a slight red tint in one area of the lamp. Over time, the condition gets worse. If you look at a unlit SOX lamp which has lost its vacuum, you will generally see a characteristic white / grey clouding on the inside of the envelope usually near to the lamp cap.

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