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Author Topic: Conductive paper in light bulb ?  (Read 580 times)

Offline FRANCO.M

  • Jr. Member
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  • Posts: 16
Conductive paper in light bulb ?
« on: June 01, 2019, 03:25:53 pm »

Hi collectors, i've found this strange light bulb.

It has an early westinghouse socket with plaster isolator, the single hairpin filament is united at platinum wire with little clamp, i think that this is an late 1880 or early 1890's bulb but  i never seen this type of conductor welded into glass.

Is similar to paper ( is transparent at light ) but is sure conductive, is a system for  elude the Edison's patent ?

Have you got any tecnical information ?

Regards, Franco.

Offline James

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    • www.lamptech.co.uk
Re: Conductive paper in light bulb ?
« Reply #1 on: July 28, 2019, 02:22:59 pm »
Hi Franco,

That is a very peculiar lamp you have found, and I think probably dates to the early 1890s when GE was taking action against smaller competing manufacturers who were infringing the Edison patents.  This period sparked a lot of ingenuity in terms of trying to circumvent the patents, and one such idea was the invention of the so-called Pollard Lamp, of which you have an example.

The Edison patents refer to hermetically sealing a metal wire through the glass to carry the electric current into the bulb.  Pollard developed a technique of coating the inside of the inner glass stem tube with silver metal powder, and then pinch-sealing this around an inner metal wire to carry the current to the filament.  Hence it brings the current into the bulb without any metal wires being sealed through the glass.

I don't know whether or not the Pollard lamp stood up in the courts and was able to escape the litigation, but by 1894 the key Edison patent had in any case expired, and manufacturers who had survived that long then quickly reverted to making lamps according to the standard design, which was certainly cheaper and easier than the complex construction like yours.

I also have a Pollard lamp, further details you can find here.