Edison GE Carbon Filament Stereopticon Projector
Since the origins of the first carbon filament lamps, they began to find uses beyond general illumination - for instance in signalling and projection apparatus. In particular, the British Ediswan company had developed a full range of flat-filament lamps for magic lanterns by the early 1890s. One of the Ediswan "Focus" lamps employed a beehive-shaped filament coil, which later became very popular in America where it was manufactured by Edison General Electric and known as the Stereopticon lamp, featured on this page.

A Stereopticon is a kind of magic lantern projector having two lenses, used for the seamless blending of one projected slide into the next. It was common in the Americas and as such the lamps for these as well as the more standard projectors quickly became known as stereopticon lamps.

The filament is intended for viewing facing the axis of the coil to achieve the most compact light source having the highest luminance, and deliver brighter projected images. Thanks to its beehive shape, the distance between adjacent coils is increased, to avoid the risk of contact or arcing during vibration or as the filament distorts during life.

The stem is ususually crowned with two extensions of rather elegant blue glass - a feature that is often found on early high power lamps. The blue glass has lower electrical conductivity when hot and reduces problems of electrolysis in the stem which may decompose the glass and cause early failure due to cracking. The leadwires are of platinum, and the filament is sealed into a spherical glass bulb having a top exhaustion tip. It is believed to date to arond 1895-1914, after which tungsten stereopticon lamps appeared.
Manufacturer: Edison Lamp Works of GE
Lamp Power: 200 Watts
Lamp Voltage: 115 Volts
Lamp Current: 1.74 Amperes
Cap Type: E26s Brass & vitrite
Bulb Type: G-950 G-30 in eighths/inch
Bulb Finish: Clear Soda-lime glass
Filament Type: Stereopticon Beehive coil
Atmosphere: Vacuum Red phosphorus getter
Luminous Flux:
Luminous Efficacy:
Beam Intensity:
Beam Distribution:
Colour Temperature & CRI: CCT: 2000K CRI: Ra 100
Chromaticity Co-ordinates: CCx: 0.527 CCy: 0.413
Rated Lifetime: 800 hours
Burning Position: Universal
Overall Length: 135 mm 55/16 inches
Light Centre Length: 89 mm 31/2 inches
Factory: Harrison NJ U.S.A.
Date of Manufacture: Approx. 1905 Date Code: h1175
Original Value: Unknown
 
References: 1) Edison & Swan Lamp Catalogue, UK, 1893, p.31.
2) Electric Incandescent Light Sources for the Magic Lantern, J.A.Davidson, The Magic Lantern Gazette, V.24 No.4 Winter 2012, pp.3-17.