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Old 27th Jul 2021, 7:26 pm   #1
dglcomp
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Default Nernst Lamps

A real rare one here, photonicinduction doesn't blow something up but takes a very careful look at some very old Nernst lamps. These are laps that were around in the carbon filaments era and use the light emission of heated ceramic to produce light, requiring a heater/ballast to get the light going, being more efficient than a carbon filament lamp.

Supposedly this is the only video online of a Nernst lamp being powered up as they are rare and extremely fragile. Very interesting, photon has quite the collection of electrical glasswear.

https://www.youtube.com/watch?v=-spTvp5-sf0

Last edited by Cobaltblue; 27th Jul 2021 at 8:42 pm. Reason: Name
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Old 27th Jul 2021, 8:18 pm   #2
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Default Re: Nernst Lamps

I saw Andy's video last night and was going to post a link here too!
He was right, I had never seen anything like it and it blew my mind.
At least a good number of us here will know what a Barretter is.

Its about the most sedate Photonicinduction video I have seen, and I prefer this style.
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Old 27th Jul 2021, 9:15 pm   #3
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Default Re: Nernst Lamps

Great stuff!

Thanks for posting,

Peter
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Old 27th Jul 2021, 9:41 pm   #4
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Default Re: Nernst Lamps

Interesting - never seen a Nernst lamp operating before.

However, maybe I’m just being too techie, but it would have been even better if he’d filled in some of the time with more information. We learned that it runs from 130 VDC, but what current was it drawing? He said it was ‘quite bright’, but how did its light output compare with, say, a 60W tungsten lamp? He told us it was very fragile, but how long did a Nernst lamp typically last in service?

It was an enterprising demo. I wonder where he got the lamp from……

Martin
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Old 27th Jul 2021, 9:41 pm   #5
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Default Re: Nernst Lamps

Love it!

(PS, I want one.)
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Old 28th Jul 2021, 12:16 am   #6
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Default Re: Nernst Lamps

Fascinating, thanks so much for posting the link! I knew they existed, but it was great to see one in operation. The Nernst lamp is described and (line) illustrated in an article in the 1910 Encyclopaedia Brittannica about illumination, and a 1970 Science Museum booklet (Lighting: 3: Other than in the home) has a colour photo of a different design of lamp from those in the video but without the glass globe or the brass cover for the barretter. The Science Museum booklet caption says:

" In 1897 Count Auer von Welsbach, of incandescent gas mantle fame, introduced a new kind of electric filament lamp which required no vacuum. The filament was a rod composed mainly of magnesia which decreased rapidly in resistance after a critical temperature was reached, but was virtually non-conducting at room temperature. Up to about 1900 a spirit lamp was used to heat the filament initially, but after that a platinum wire wound round a ceramic spiral was used as a heating element and cut out by a simple electro-magnetic relay as soon as the main filament current rose sufficiently to indicate that the lamp was well alight. Because there would have been difficulty in operating the relay from an alternating current source the lamps were normally restricted to direct current supplies.

Resistance to the filament decreased so rapidly with temperature that it was necessary to put into the circuit an iron wire barretter resistance ( an evacuated bulb on top of the lamp) which increased in resistance as the current rose. Efficiency was about 6 - 8 lumens per watt, and the filaments were normally enclosed by a glass globe for protection while the barretter was enclosed by a metal tube (not shown). As the glass globe was not essential these lamps later became a source of radiation for infra-red spectroscopy. "


N.B. The Science Museum booklet photo seems to be upside-down, as the barretter is depicted below the filament assembly.

Last edited by emeritus; 28th Jul 2021 at 12:28 am. Reason: typos
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Old 28th Jul 2021, 3:51 am   #7
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Default Re: Nernst Lamps

I once repaired an infra-red spectrometer where the light source was a Nernst glower. The advantage in that application was that the glowing bit didn't have be inside an (evacuated) glass bulb. so there was nothing to absorb the infra-red radiation.

The ballast was a box containing officially 3 0.3A barretter lamps with switches to select 0.3A and 0.6A, both on giving 0.9A of course. When the bulbs failed we fitted normal 60W bulbs which seemed to work.

Anyway, the startup procedure was interesting. There was no heater coil on the Nernst element. Instead you opened up the lamphouse, took a screwdriver, put bit of cotton wool on the end, soaked it in ethanol and lit it. Then used that to heat the Nernst element. When it started to glow you removed the screwdriver and closed the lamphouse. Remember that the Nernst element was connected to the mains...

I don't know the date of the instrument, but it can't have been all that old (1960s?) The amplifier unit was mostly valved, but there was an OC-something-or-other transistor in there too.
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Old 28th Jul 2021, 9:11 am   #8
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Default Re: Nernst Lamps

Interesting that the spectrometer used what was essentially the pre-1900 starting technique. I guess that, for the spectometer, there was not the need for the quasi-instant start that was desirable for room lighting, and it eliminated the need for expensive platinum.
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Old 28th Jul 2021, 9:48 am   #9
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Default Re: Nernst Lamps

When I was at university (from 1974 to 1981) the IR spectrometer used a Nernst glower. The trick for long life was not to turn it off. It would last about a year, and I kept a small stock of the things to keep the spectrometer operating.

I needed the spectrometer functional because I was working at wavelengths up to 20um, and so needed it to check and calibrate the transmission spectrum of the optics.

I forget entirely what brand that Spectrometer was. Almost certainly a 1960's vintage instrument.

Craig
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Old 28th Jul 2021, 12:27 pm   #10
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Smile Re: Nernst Lamps

Hi,
Here's another YouTube video about these fascinating Nernst lamps.

https://www.youtube.com/watch?v=1vCQySb6ulA

Cheers, Pete
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Old 28th Jul 2021, 3:57 pm   #11
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Default Re: Nernst Lamps

Very generous of Andy to devote so much time to YT, the previous clip summarised (some rare) fluorescent tubes, eg coloured ones with bayonet caps, half-phosphored ones, etc. Also a demo of just how little inert gas is actually present in a T12- only about 2 or 3% by volume.

The few Nernst type lamps for sale online are several hundred quid- and almost certainly broken!

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Old 28th Jul 2021, 4:11 pm   #12
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Default Re: Nernst Lamps

After seeing the video the OP kindly posted, I read up a bit on the Nernst glower, zirconium and yttrium oxides were used.

For lamp mantles (gas, and paraffin), the oxides used were thorium with a small amount of cerium, to give a good light. I'm wondering why these were not used in the Nernst - maybe just because of conductivity (or lack of?)

Quote:
Originally Posted by The Philpott View Post
...how little inert gas is actually present in a T12- only about 2 or 3% by volume
That can't be right - a gas always fills its container! So they're 100% full.

Does it mean that the gas inside is at 2 or 3% of atmospheric pressure?
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Old 28th Jul 2021, 6:30 pm   #13
G.Castle
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Default Re: Nernst Lamps

Clever device, very interesting to see the lamp working as intended, thanks for posting a link
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Old 28th Jul 2021, 6:40 pm   #14
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Default Re: Nernst Lamps

As a modest collector of vintage light bulbs I am fascinated by this lamp. I never knew it existed. The Hydrogen filled ballast barretter, in a very similar form was used as a heater regulator in GEC and English Electric TV receivers from the early 50's to around 1956. John.
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Old 28th Jul 2021, 7:53 pm   #15
The Philpott
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Default Re: Nernst Lamps

Post No.12- Terminology glitch by me there; he tested how hard the vacuum was by submersing the bottom end of the 'tube in (dyed) water then snipping the crimp off the end. It was surprising how much water was pulled in!

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Old 29th Jul 2021, 6:38 am   #16
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Default Re: Nernst Lamps

As I have an interest in lighting of all kinds this was absolutely fascinating! They knew a thing or two back in the day, far more than, I think, we give them credit for. Never heard of a Nernst lamp before let alone seen one operating. Many thanks for posting & broadening my knowledge & understanding.
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Old 29th Jul 2021, 12:50 pm   #17
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Default Re: Nernst Lamps

I have inherited (many years ago) a box of 2 Nernst filaments neatly wrapped in cotton packing. For ages I didnít give them a second thought amongst all the other stuff I have accumulated over the years but it is great to see a renewed interest in this older technology. The lamps I have seen ( again on YouTube etc) show a complex light fitting with a bimetallic time switch that pre heats the Nernst filament before it is powered.
I would post a picture of them but I in Japan working on a well known spectator free event. Iíll put some up when I get home.
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Old 29th Jul 2021, 3:50 pm   #18
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Default Re: Nernst Lamps

There was, and may still be, a Nernst lamp on display in the science museum London.

As has been said, Nernst lamps are now rare. Has anyone tried making a working replica ? Possibly easier than a filament lamp as no high vacuum pumping plant is needed.

Nichrome wire might serve for the preheating element rather than very costly platinum.
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Old 29th Jul 2021, 4:33 pm   #19
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Default Re: Nernst Lamps

Quote:
Nichrome wire might serve for the preheating element rather than very costly platinum.
Or a flame as said before. I wonder if a gas/paraffin mantle would work if scrunched up enough? I have some Tilly mantles I may give it a go in a moment of madness.
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Old 29th Jul 2021, 4:39 pm   #20
TonyDuell
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Default Re: Nernst Lamps

Be warned that some of those gas mantles contain thorium oxide and are quite radioactive. Make sure you don't breath any dust from them, for example.

As I menitoned, a mains fillament lamp (you lamp limiter?) will work as a ballast at least for testing.
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