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Philips 250w MBTL Lamp

Philips 250w MBTL Lamp

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Philips 250w MBTL Lamp

Blackening that took place after roughly 20 minutes of operation.

IMG_9051.JPG IMG_8260.JPG IMG_8213.JPG IMG_8082.JPG

Light Information

Light Information

Manufacturer:Philips
Lamp
Lamp Type:Self ballasted mercury
Base:E40
Electrical
Wattage:250
Physical/Production
Factory Location:Gt. Britain

File information

File information

Download: Download this File
Filename:IMG_8213.JPG
Album name:Andy / Mercury Lamps
Keywords:Lamps
File Size:304 KB
Date added:Sep 10, 2018
Dimensions:2464 x 1848 pixels
Displayed:132 times
Date Time:2018:08:19 15:25:34
DateTime Original:2018:08:19 15:25:34
Exposure Bias:0 EV
Exposure Time:1/400 sec
FNumber:f 3.2
Flash:No Flash
Focal length:5 mm
ISO:100
Make:Canon
Model:Canon IXUS 132
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Comments
tuopeek
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Tuopeek-475652085781113 tuopeek1 77334065@N05/
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Sep 10, 2018 at 12:39 PM Author: tuopeek
Oh, that's a bit of a shame. I had something like this happen in a tungsten ballasted lamp, I think some air or actually oxygen must have seeped in. Still a lovely example though.
sox35
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Sep 10, 2018 at 01:49 PM Author: sox35
A lovely lamp, I do love these half-coated examples. A pity about the blackening, it's still a good display lamp, though

Ria in Aberdeen
It'll be all right in the end, and if it isn't all right, it isn't the end  Smiley

Valve 72
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Sep 10, 2018 at 01:55 PM Author: Valve 72
That's sad, it's such a lovely lamp.
James
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Sep 10, 2018 at 02:33 PM Author: James
Aww such a pity, but its still an outstanding lamp. The blackening is caused by the water cycle, which particularly affects mercury blended lamps.

If it was a big air leak the tungsten would oxidise to tungsten trioxide (WO3) and create a yellowish smoke on the glass. A small air leak would create the low tungsten oxide W2O5 which is blue-violet. The deposition in such lamps stops after all the oxygen has been consumed.

But here the deposit is black, so pure tungsten. This is caused by minute traces of water, which tend to come out of the quartz arc tube. The heat of the filament then cracks the water into oxygen and hydrogen. The oxygen reacts with the filament, evaporates, and is deposited on the bulb as above. The free hydrogen then reacts with the tungsten oxide, reducing it to the black tungsten metal deposit you can see, and forming more water. Then the cycle begins again with the cracking of that new water to go and attack the filament over and over again - hence the water cycle. It will continue until the filament burns out.

The way to stop this cycle is to include a getter for hydrogen in the outer bulb. These days that takes the form of a zirconium-aluminium getter pan eg. Type St101 from Saes Getters or the Chinese equivalent from Nanjijng Getter. Older lamps used a piece of wire made from zirconium or titanium, usually in the form of a coil on the support frame alongside the arc tube. I do not see either in this lamp - perhaps it was forgotten.
Andy
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Sep 11, 2018 at 06:39 AM Author: Andy
Thanks for that explanation of what has happened. Needless to say the lamp will not be lit again sadly.
I didn't think it was just a simple case of an air leak as I have experienced that before on a 300w GLS lamp - The filament immediately gave off lots of yellow smoke for about 5 seconds before breaking.
I wouldn't have considered the culprit to be water but your explanation makes perfect sense and brings back my somewhat vague memories of A level Chemistry lessons.
There is no getter of any sort that I can see in this lamp.

My main area of interest is vintage fluorescent and mercury lamps. Always interested in doing lamp trades - just let me know! Smiley

sox35
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Sep 11, 2018 at 08:47 AM Author: sox35
Very strange there's no getter, at least now we know what happened. I know what you mean about the yellow smoke, that's what happened to Thomas when the glass cracked and air got in

Ria in Aberdeen
It'll be all right in the end, and if it isn't all right, it isn't the end  Smiley

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Sep 11, 2018 at 09:04 AM Author: Cal
I wondered about the lack of getter too. At least the filament still lives intact.
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