Edison First Commercial Carbon Lamp

This historic lamp illustrates the earliest commercial design made by Edison from late 1879 to early 1880, after the first experimental models of early 1879. About a hundred were made to illuminate the Menlo Park laboratories for a public demonstration in December 1879. There are some doubts concerning its provenance, and recent discoveries suggest that it may be an extremely good replica made by Edison's assistant Francis Jehl around 1928-30, when the Menlo Park lab was re-built at Henry Ford's Greenfield Village museum.

The filament is made from Bristol board cut into a horseshoe shape with widened ends, and carbonised. This hopelessly delicate article is mounted with the aid of small metal clamps fastened around its ends, these being tightened with tiny bolts to exert the required pressure. The clamps are made from a dark or oxidised metal, which seems unusual as known originals have shiny clamps, possibly of platinum. The end of each clamp is pierced by a platinum wire which extends into a bulbous glass stem. Presumably in an effort to improve the quality of the glass-to-metal seal, a small bead of white glass is present around each of the wires. An olive formed further down the stem widens its diameter for sealing to the bulb, which has been free-blown in lead glass.

The stem is continued to form the base, whose terminals consist of diametrically opposed lateral copper strips. Small copper wires connect these to the platinum at a twisted joint inside the stem. The terminals are fastened in place with cotton thread at one end, and at the opposite end with the aid of a small cork wedged into the open end of the glass tube. This design was manufactured and sold until early 1880 when it was replaced by an improved construction.

Manufacturer:	Edison Electric Light Company
Lamp Power:	Approx. 70 Watts
Lamp Voltage:	Approx. 115 Volts
Lamp Current:	Approx. 0.6 Amps
Cap Type:	Copper Slide Terminals	Cork stopper
Bulb Type:	GA-64	GA-20 in eighths/inch
Bulb Finish:	Clear	Leak-alkali silicate glass
Filament Type:	Carbonised Bristol Board	Horseshoe shape
Atmosphere:	Vacuum	No Getter
Luminous Flux:	Approx. 60 lumens	Approx. 5 candle power
Luminous Efficacy:	Approx. 1.4 lm/W
Beam Intensity:	N/A
Beam Distribution:	N/A
Colour Temperature & CRI:	CCT: Approx. 2000K	CRI: Ra 100
Chromaticity Co-ordinates:	CCx: 0.527	CCy: 0.413
Rated Lifetime:	Approx. 2000-3000 hours
Burning Position:	Vertical only	(to avoid filament sag)
Overall Length:
Light Centre Length:
Factory:	Menlo Park NJ, USA	or Greenfield Village MI, USA
Date of Manufacture:	1879 - 1880	or c.1928-30
Original Value:	Unknown


References:	1) The Electric Lamp Industry, A.A. Bright, publ. The Macmillan Company 1949, p.122, 134
	2) Chad Shapiro, private communication, May 2022