Ediswan Thermalite Carbon Heater
The first electric heaters were based around high power single-ended carbon filament lamps, commonly known as the Dowsing Radiator. They were physically large lamps and even using a polished metal reflector, it was not possible to collimate their rays of heat into a small area. As such they were primarily used for domestic heating applications.

This unusually high power compact carbon lamp would be used in a shallow bowl-type parabolic reflector, to collimate its rays and produce a narrow beam of heat. Such devices were pioneered by the Belling Heat Company and typically featured a copper reflector. This low voltage version is believed to have been produced for industrial heating, such as drying lamps. The packaging style dates its production to the period 1927-1936. The bulb is acid-etched 'Menley & James Ltd.', a manufacturing chemist which became famous as the first British producer of Aspirin. It is possible that they were a large consumer of such lamps, which warranted the marking of their name on the bulbs to avoid pilfering.

Such lamps were largely phased out following the 1905 invention of chromel / nichrome, a nickel-chromium alloy which resists oxidation up to dull red heat without requiring an evacuated glass bulb. Retrofit devices were made in which the resistance wire was coiled around a conical ceramic former, being equipped with a screw base to fit the old heater units. The carbon lamps did however remain in large scale production until as recently as the 1990s. One of their final applications was as therapeutic lamps requring the combination of light plus heat. They were often made in red and blue glass bulbs to allow the transmission of only certain wavelength ranges, and were especially popular in Europe.
Manufacturer: Royal Ediswan
Lamp Power: 200 Watts
Lamp Voltage: 50 Volts
Lamp Current: 4.00 Amperes
Cap Type: E27s Brass & Vitrite
Bulb Type: G-88 G-27¾ in eighths/inch
Bulb Finish: Clear Soda-lime glass
Filament Type: Carbon 3.5 loop
Atmosphere: Vacuum Red P getter
Luminous Flux: 300 lumens
Luminous Efficacy: 1.5 lm/W
Colour Temperature: 1950 K
Colour Rendering: Ra 100
Chromaticity Co-ordinates: CCx: 0.530 CCy: 0.408
Lifetime: Approx. 800 hours
Burning Position: Universal
Overall Length: 133 mm 51/4 inches
Light Centre Length: 90 mm 31/2 inches
Factory: Ponders End England
Date of Manufacture: 1927-36 Date Code: 701
Original Value:
References: 1) Photoelectric measurement.
2) The History of Electric Heating, Electric Radiators Direct, UK.
3) Belling & Co. Ltd., Grace's Guide to British Industrial History.