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WWII DUNGENESS LIGHT HOUSE SPARE LAMP
Removed from the lighthouse during WW2 and held in storage since then.
It was removed to prevent subversive organisations from using the light for signalling in the event of an invasion.
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- My Father was an Assistant Keeper at Dungeness Lighthouse 1954-68 and he gave me one of these bulbs when the glass became loose in the copper base and it was replaced. I have still have it and was interested to read the technical information about its design and use.
.......... David Caldwell-Evans, London, 23rd of March 2016
- This is a lamp known as the type EC111, manufactured by Osram-GEC at Wembley. It is rated 240 Volts and 3000 Watts. It is of a rather unique construction for incandescent lighthouse lamps, because instead of containing the usual one or two large filaments, it contains six smaller filaments each rated 500 Watts. These are arranged in three pairs, each pair being mounted separately to form a cylindrical arrangement. The reason for using several small filaments instead of one large coil is that their thermal mass is reduced - i.e. they heat up and cool down more quickly. This was an important step forward which simplified lighthouse design.
Until the development of this lamp, lighthouses produced their pulsating signal by using a static lamp which burns continuously, disposed at the centre of a rotating optical assembly which sweeps out a beam of light around the tower thus giving a flashing effect from a fixed viewpoint. The large rotating optics are complex and expensive to build, but were necessary right from the beginning of lighthouses because of the difficulty of flashing on and off the early light sources based on fire / combustion of gas/oil etc. Even with the advent of incandescent lamps, flashing remained difficult because the thermal mass of their huge high-power filaments was such that they take several seconds to cool down after switch-off, with the result that individual flashes of light would be blurred together.
Osram-GEC solved the problem by introducing this multi-filament lamp. The small individual filaments have lower thermal mass and can be flashed on and off at suitably high speeds with a simple electrical controller. Dungeness Lighthouse has historically been the site used by Trinity House Corporation for the trialling of new light sources, and it was the first place where this so-called EC111 lamp was installed.
Later in the 1970s it was superseded by a superior lamp type EC111A developed by Thorn Lighting, which employed 4x 750W filaments in a box configuration and was much easier to construct (and less fragile) than the GEC's original design.
Later still, Dungeness was the first lighthouse to be converted to use of a Xenon Arc as its light source. Since arc lamps have no filament to heat up, the light can be pulsed on and off near-instantaneously. Discharge lamps are now used almost universally in the British Lighthouses.
.......... James Hooker, Aarschot, Belgium, 30th of April 2011