In a museum in Germany, I saw this lightbulb-shaped device mounted in a E27 mount, seemingly on 230V AC. It contained a thick black spiral, with a visible gap at the top, emitting a soft deep orange glow when switched on. It was definitely not bright enough to have been used for general lighting (or perhaps degraded over the years so that it is no longer bright?), as seen when compared to a normal 40W bulb in the second picture. The glass seemed darkened, perhaps by something ablating from the spiral.

Any ideas what this is?

Image of the device in question Brightness comparison

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    \$\begingroup\$ Is it somewhere that a low power heater would be useful (e.g. to keep water pipes from freezing) in a semi-outdoor area? \$\endgroup\$ – user_1818839 Jun 24 '20 at 15:48
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    \$\begingroup\$ Looks very Neon-ish. If so, it contains low-pressure neon gas. I'd guess a current-limiting series resistor resides in the base. Very low-power and very little heat generated. Tested with an ohmmeter, it would register "infinite" ohms (if I've guessed right) \$\endgroup\$ – glen_geek Jun 24 '20 at 15:51
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    \$\begingroup\$ How much heat does the bulb produce? Any chance that it is a heater? \$\endgroup\$ – Dwayne Reid Jun 24 '20 at 15:56
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    \$\begingroup\$ Oh. Somehow I didn't see that bit about the museum. \$\endgroup\$ – JRE Jun 24 '20 at 16:44
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    \$\begingroup\$ As @jsotola notes - there seem to be two non touching interleaved spirals. If so this strongly suggests a gas discharge rube - probably Neon - often used as a voltage indicator. The purposeful effort to increase the area between the two conductors does suggest that the light output may have been valued - so use as a darkroom lamp or similar seems possible. \$\endgroup\$ – Russell McMahon Jun 25 '20 at 17:47

Jsotola noted that the lamp has two separate electrodes.
This is a form of Neon or Argon "glow filament lamp". The term Aerolux is also used. There are quire a few examples on web once you know what to look for.

This is described as "Here you see a Vintage Osram (G.E.C.) 200/250 volt NEON (Beehive) Nightlight Lamp with B22d (BC) cap, with Clear Bulb circa 1950's" from here

You can see the two interleaved non contacting spirals intended to maximise the area of glow discharge and hence light output. enter image description here

THey are also used as "artwork" with glowing shapes and figures.
Various examples here


A more normal electrode shape but also used as a lamp - "A General Electric NE-34 glow lamp, manufactured circa 1930"

enter image description here


  • Around 1917, Daniel Moore developed the neon lamp while working at the General Electric Company. The lamp has a very different design from the much larger neon tubes used for neon lighting. The difference in design was sufficient that a U.S. patent was issued for the lamp in 1919.[4] A Smithsonian Institution website notes, "These small, low power devices use a physical principle called coronal discharge. Moore mounted two electrodes close together in a bulb and added neon or argon gas. The electrodes would glow brightly in red or blue, depending on the gas, and the lamps lasted for years. Since the electrodes could take almost any shape imaginable, a popular application has been fanciful decorative lamps.[5]

  • Glow lamps found practical use as indicators in instrument panels and in many home appliances until the widespread commercialization of light-emitting diodes (LEDs) in the 1970s.[5]

Vintage Soviet Light Bulb Aerolux Neon Filament Glow Lamp Spiral - source link broken

enter image description here

In his answer 7kasper provides this useful link.

It notes "Application: Lighting of Hospital Wards, Nursaries, Childrens Bedrooms and General Night Lighting"

Key factoids from that site relating to the bulb he shows but generally applicable include:

Lamp Type: Neon Glow Lamp
Filament/Radiator Type: 2 x Spiral Electrodes
Service Life: 10000 Hours
Fixture Type: General Domestic & Hospital Night Lights
Ballast Type: Internal Resistor
Wattage: about 5 watts
Current: Very Little [ :-) ] Color Temperature: Orange
Color Rendering Index: Unknown
Fabrication Date: 1950's
Application/Use: Lighting of Hospital Wards, Nursaries, Childrens Bedrooms and General Night Lighting

  • \$\begingroup\$ Combined with a comment from @7kasper‘s link, above, that those were used as long-lived nightlights in childrens‘ rooms, staircases, hospitals and so on, I think we have a winner. Very interesting! \$\endgroup\$ – jstarek Jun 26 '20 at 18:15

My first bet was that they were all just incandescent lightbulbs. Where the right most lamp has perhaps a bit of air seeped in the vacuum bulb and the tungsten started to burn a bit. However these spirals are not a form which incandecents are made. Much more likely it is a neon lamp. Here is another one:



  • \$\begingroup\$ It doesn't really look like the pne in the middle \$\endgroup\$ – Sim Son Jun 24 '20 at 20:31
  • \$\begingroup\$ Yeah that's true. I will edit the comment a bit. \$\endgroup\$ – 7kasper Jun 24 '20 at 20:31
  • \$\begingroup\$ That looks pretty much like it, thanks! However, can you elaborate on the details of such a form of neon lamp? I am only familiar with the shape and properties of neon tubes. And what about that very thick "filament", do you know about the material used, its properties and so on? \$\endgroup\$ – jstarek Jun 25 '20 at 6:30
  • \$\begingroup\$ +1 | Good link. They say " Lighting of Hospital Wards, Nursaries, Childrens Bedrooms and General Night Lighting" \$\endgroup\$ – Russell McMahon Jun 27 '20 at 7:00
  • \$\begingroup\$ I've added content from your link to my answer. If you want to you can copy the material from the end of my answer (edited if desired) and if you do I'll delete it from my answer. Please let me know if you do this. \$\endgroup\$ – Russell McMahon Jun 27 '20 at 7:05

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