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Imperial-brand Double Hairpin carbon filament lamp Voltage- 110-120v Wattage/rating- ? Filament- Carbon, Double Hairpin Cap type- US Std base Circa- ~1905 Finish- Clear glass Origin- USA Imperial brand Double hairpin lamp. First introduced in 1905, these used "GEM" filaments which were metalised carbon that had a lower resistance than normal carbon, and burned brighter. Since the resistance was lower, they needed to have a longer length of filament inside to run from the mains voltage so the Double Hairpin design was adopted- essentially 2 identical filaments connected in series. Although the outer label is long gone, the internal construction gives its origin away. The manufacturers of these lamps made them in slightly different ways. Edison/GE`s lamp had just 3 points where the filament attached- one at each end where the power comes in and one in the middle where both filaments join. Imperial`s lamp uses 4 points to attach the filament- each end of each filament is joined seperately. The two central pins are interconnected (they are made of one single piece of wire set into the stem) and you can just see the wire looping round in the closeup of the stem below. Double Hairpin lamps are quite scarce- about 4 years after they were introduced, all GEM carbon lamps were changed to a simpler single continuous filament looped round inside, usually with a central support. These later looped carbons however, are quite commonly found.

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