Robertson Infrared Carbon Radiator
Incandescent lamps have long been used as a source of heat, on account of the fact that they are tremendously inefficient convertors of electrical energy into visible light. Despite their powerful thermal radiation, the design can still be improved so as to make it an even better heat source.

One of the earliest applications of heat lamps was pioneered by General Electric of USA in 1893, which introduced the first domestic electric fire. It was engineered around what later became more commonly known as the 'Dowsing' or 'Sausage' lamp featured on this page. H.J. Dowsing was a British pioneer who established the Dowsing Radiant Heat Company to capitalise on the advantages of these lamps, and became so prolific in selling domestic heating apparatus that the lamps soon became known as Dowsing lamps.

It comprises two long hairpin-shaped carbon filaments, supported by wire loops attached to a central glass stem. See X-Ray - the filament itself is not visible due to its low absorption. It was standard practice to connect the filaments in parallel for 100-130V mains and in series for 200-260V. There were clearly large tolerances - this example drawing 335W despite its 250W rating. The earliest lamps were clear, then shifting to a frosted bulb to reduce glare. This later model features a reddish iron oxide coating to create an atmosphere of cosiness and warmth similar to a coal fire.

After the 1905 invention of chromel / nichrome, a nickel-chromium alloy which resists oxidation up to dull red heat, it became possible to simplify domestic heaters and they shifted to open resistance elements. However, replacment carbon heater lamps remained in production until the 1960s.
Manufacturer: The General Electric Company of England
Lamp Power: 335 Watts
Lamp Voltage: 230-250 Volts
Lamp Current: 1.40 Amperes
Cap Type: B22d/35x38 Brass & Vitrite
Bulb Type: T-57 T-18 in eighths/inch
Bulb Finish: Flame-tint Soda-lime glass
Filament Type: 2S-2 Twin carbon hairpin
Atmosphere: Vacuum Red P getter
Luminous Flux: 125 lumens
Luminous Efficacy: 0.37 lm/W
Colour Temperature: N/A
Colour Rendering: Ra 75
Chromaticity Co-ordinates: CCx: 0.600 CCy: 0.365
Lifetime: Approx. 1000 hours
Burning Position: Vertical
Overall Length: 285 mm 111/2 inches
Light Centre Length: 185 mm 71/4 inches
Factory: Hammersmith England
Date of Manufacture: 1940 September Date Code 81
Original Value: £0 4s 3d 1937
References: 1) Photoelectric measurement.
2) Osram-GEC Catalogue, 1932, UK, p.17.
3) Osram-GEC Catalogue, 1937, UK, p.35.
4) Osram-GEC Catalogue, 1951, UK, p.55.
5) Osram-GEC Catalogue, 1959, UK, p.14.
6) Osram-GEC Catalogue, 1960, UK, p.18.
7) Osram-GEC Catalogue, 1962, Australia, pp.26-27.
8) The History of Electric Heating, Electric Radiators Direct, UK.
9) Biography of Herbert John Dowsing, Grace's Guide to British Industrial History.
10) Dowsing Radiant Heat Co., Grace's Guide to British Industrial History.
11) GEC Electric Fire featuring Dowsing Flame-tint lamps, Science Museum Collection, London.