Edison Bamboo Filament with Copper Clamps

This lamp is representative of the type in production at the Edison Company between the years 1884 and 1886. A number of its features help to date it to this period.

Prior to 1884 all Edison lamps employed a strain relief ring of plaster-of-paris between the base and bulb, not present here. The type of base on this lamp was used from 1884-1888. From 1888-1894 it was superseded by a longer type having more screw threads, whose open end was spun in to a smaller diameter to yield a stronger bond to the bulb.

The filament is a carbonised bamboo strip of rectangular cross-section, having enlarged ends. It is of Japanese Madake bamboo. This was in production from 1880 to 1886, after which thinner square-section filaments were adopted.

Another identifier is the method of affixing the filament to the platinum leading-in wires. These have been flattened at their extremities and crimped around the filament, the joint then being fixed by electroplating a layer of copper over the whole. This method was used between 1881 and 1886, after which the carbon paste joint was introduced.

The leading-in wires are made of platinum throughout the whole stem, a method that was used until 1890. Thereafter the weld to the external lead-wires was included in the glass stem press to reduce the required length of platinum.

The bulb is of a type free-blown in the air from 1” diameter tubing. Moulded bulbs were not introduced until 1892. It is sealed to an enlarged olive-section in the stem. The bulb shows the classic rounded tip, common to Edison lamps.
Manufacturer: Edison Lamp Company
Lamp Power: Approx. 72 Watts
Lamp Voltage: 110 Volts
Lamp Current: Approx. 0.65 Amperes
Cap Type: Edison Screw Open top 1884-1888 style
Bulb Type: SA-56 SA-18 in eighths/inch
Bulb Finish: Clear Soda-lime glass
Filament Type: Bamboo strip, rectangular Enlarged end sections
Atmosphere: Vacuum No getter
Luminous Flux: 201 lm 16 Candle Power
Luminous Efficacy: 2.8 lm/W 4.47 Watts per Candle
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 120 hours
Burning Position: Vertical only (to avoid filament sag)
Overall Length: 140mm 5¼ inches
Light Centre Length: 82mm 3¼ inches
Factory: Harrison, NJ U.S.A
Date of Manufacture: 1884 - 1886
Original / Present Value: Unknown Unknown
References: 1) The Electric Lamp Industry, A.A. Bright, publ. The Macmillan Company 1949, p.123