Maxim Carbon Filament Lamp

The American inventor Hiram Maxim was one of the earliest contributors to the development of the incandescent lamp. His designs are particularly distinctive on account of the M-shaped filament, which is often speculated to have been chosen in view of its similarity to the first letter of his name. They were first produced in 1879 by the United States Electric Lighting Co. which had been established a year earlier in New York with Maxim as chief engineer, until perhaps as late as 1888 when it was taken over by Westinghouse. In 1881 Maxim emigrated to England, and established his own independent lamp works in London.

This lamp is of quite different appearance than the typical long-necked American versions. Its platinum loop terminals and round bulb are more typical of Swan and other British lamps, a design which was not widely adopted in USA. It is therefore suspected that this lamp may be of UK origin.

The filament is of carbonised paper and the leading-in wires are platinum throughout. The method of filament mounting is typical of Maxim lamps. He disliked the usual deposited carbon or electroplated joints of this era, fearing premature failure at the junction. To reduce temperatures at the joint as well as provide a large contact area, the filament tails are greatly enlarged. These are compressed tightly against the flattened lead-wires and sandwiched between a pair of platinum washers with the aid of tiny nuts and bolts. Maxim was also the inventor of the so-called flashing process, in which the filaments are first lighted in gasoline vapour. This forms a deposit of carbon over the filament, particularly in the area of hot-spots, to achieve a more uniform cross-section and allow it to be driven at higher efficacy.

Manufacturer:	Maxim Lamps (or US Electric Lighting Company?)
Lamp Power:	32 Watts	(at 50 Volts)
Lamp Voltage:	50 Volts	(estimated)
Lamp Current:	0.64 Amperes	(at 50 Volts)
Cap Type:	Bottom Loop	Platinum wires
Bulb Type:	G-64	G-20 in eighths/inch
Bulb Finish:	Clear	Leak-alkali silicate glass
Filament Type:	Carbonised Paper	Flat M-shape
Atmosphere:	Vacuum	Trace gasoline vapour
Luminous Flux:	c. 80 lm	(at 50 Volts)
Luminous Efficacy:	c. 2.5 lm/W
Beam Intensity:	N/A
Beam Distribution:	N/A
Colour Temperature & CRI:	CCT: Approx. 2000K	CRI: Ra 100
Chromaticity Co-ordinates:	CCx:	CCy:
Rated Lifetime:	Unknown
Burning Position:	Vertical only
Overall Length:	88 mm	3.5 inches
Light Centre Length:	45 mm	1¾ inches
Factory:	London, England	(or Bridgeport CT, USA?)
Date of Manufacture:	c. 1883-1890
Original / Present Value:	Unknown


References:	1) Evolution of the Electric Incandescent Lamp by F.L. Pope, publ. Boschen and Wefer (New York) 1894, pp.77-81.
	2) Electric Illumination Vol. II by James Dredge, 1885, pp.658-661.
	3) The History of N.V. Philips Gloeilampenfabrieken by A. Heerding, publ. Cambridge University Press 1985, pp. 16-17, 88-89.
	4) Lengthening the Day by Brian Bowers, publ. Oxford University Press 1998, p.87 and 99.
	5) Edison's Electic Light : Biography of an Invention by R. Friedel & P. Israel, Rutgers University Press 1987, p.115.
	6) Profile of Hiram S. Maxim, by Ed Covington
	7) Description of similar lamp on website of Tim Tromp
	8) US Patent 230,310, 20th July 1880, "Electric Lamp", Hiram Maxim, assignor to Joseph D. Schuyler of New York.
	9) US Patent 247,085, 13th September 1881, "Process of Manufacturing Carbon Conductors", Hiram Maxim, assignor to US Electric Lighting Co. of New York.