Robertson Carbon Heater 65W
Long after the obsolescence of the original carbon filament lamps for general lighting applications, their production continued on a smaller scale for their secondary applications as electrical heaters and resistances. The carbon lamp, having a lower luminous efficacy than its tungsten successor, naturally produces a greater proportion of its radiation in the infrared spectrum and therefore makes a better heater. Their reduced luminous flux is often also beneficial in terms of avoiding glare in heating applications. Another spinoff use of the carbon filament lamp was as a convenient high power electrical resistor. They have the advantage of not requiring a metallic heatsink, as used with typical wirewound power resistors.

Carbon Heater lamps were especially popular in scientific and school laboratories as a convenient source of heat. They were also used in resistance boards for a variety of applications - once again in school laboratories, as well as for the control of older electrical equipment.

The UK demand for such lamps was produced by two manufacturers : Robertson, which was a part of the General Electric Company of England, and Ediswan, which was a part of Associated Electrical Industries and later Thorn Lighting. Both companies produced high power Dowsing Radiator lamps, as well as GLS-type lamps in 65W, 130W and 200W ratings which were approximately based on the 16, 32 and 50 candlepower carbon illumination lamps. This relatively old Robertson lamp was produced shortly after WW2, and its production was continued by GEC and later Victory Lighting until around 2003. Thorn Lighting abandoned its carbon heater production in the early 1980s.
Manufacturer: The General Electric Company of England
Lamp Power: 65 Watts
Lamp Voltage: 240-250 Volts
Lamp Current: 0.27 Amperes
Cap Type: B22d/25x26 Brass+vitrite
Bulb Type: PS-60 PS-19 in eighths/inch
Bulb Finish: Clear Soda-lime glass
Filament Type: Carbon 3½ loop
Atmosphere: Vacuum Red P getter
Luminous Flux: 75 lumens
Luminous Efficacy: 1.15 lm/W
Colour Temperature: 1950K
Colour Rendering: Ra 100
Chromaticity Co-ordinates: CCx: 0.527 CCy: 0.407
Lifetime: Approx. 800 hours
Burning Position: Universal
Overall Length: 285 mm 111/2 inches
Light Centre Length: 152 mm 6 inches
Factory: Hammersmith England
Date of Manufacture: 1949 January Date Code: 85
Original Value:
References: 1) GE USA Large Lamp Catalog, 1948, p.30.
2) GE USA Large Lamp Catalog, 1954, p.62.
3) GE Blacklight Lamps Brochure, 1970, USA.
4) Lamps for a Brighter America, P.Keating, McGraw-Hill Book Company Inc, 1st Edition (1954) p.205.