Thorn Infrared Reflector Hardglass Spot
Incandescent lamps have long been used as a convenient source of heat. Even in the 1890s manufacturers offered high power carbon lamps for domestic radiators. However it it was not until the late 1930s that filament lamps suddenly gained popularity for industrial heating, following the pioneering work of Ford with standard incandescent lamps to accelerate paint drying in its automobile production.

The first industrial infrared lamps were made in spherical bulbs for use with an external reflector. However, following the invention of the aluminised blown-reflector lamp, it was a logical step to produce infrared lamps with integrated reflector. This very much simplified the arrangements in infrared paint drying tunnels, and allowed a significant increased in irradiation levels due to the closer spacing that became possible between adjacent lamps.

Initially the infrared reflector lamps were made in soft glass bulbs, even up to the most powerful 375W rating. Their high operating temperature rendered them liable to shatter with some violence if splashed with liquids or touched against cold objects whilst in operation, due to the low thermal shock resistance of soda-lime type glasses. That problem was overcome with the lamp featured here, which employs a hard glass borosilicate bulb which is considerably more resistant to thermal shock. However this also increased lamp cost by around 40%, hence the hardglass types are mainly for domestic use whereas industrial customers tend to prefer the cheaper softglass lamps. The filament is a coiled-coil design operating at 2500K to produce the optimum wavelengths for domestic heating. A mica baffle plate in the lamp neck serves to limit the cap temperature rise.
Manufacturer: Thorn Lighting Ltd.
Lamp Power: 275 Watts
Lamp Voltage: 200-250 Volts
Lamp Current: 1.1 Amperes
Cap Type: B22d/25x26 Brass + vitrite
Bulb Type: R-125 R-40 in eighths/inch
Bulb Finish: Clear aluminised Borosilicate glass
Filament Type: CC-9 Wreath
Atmosphere: 85:15 Argon-Nitrogen Red P & ZrAl getters
Luminous Flux: 1920 lm (2420 lm clear bulb)
Luminous Efficacy: 7.0 lm/W (8.8 lm/W clear bulb)
Beam Intensity: N/A
Beam Distribution: N/A
Colour Temperature & CRI: CCT: 2500K Ra 100
Chromaticity Co-ordinates: CCx: 0.478 CCy: 0.414
Lifetime: 5000 hours
Burning Position: Universal
Overall Length: 175 ± 3.5 mm 67/8 inches
Light Centre Length: 106 mm 41/8 inches
Factory: Buckie, Inverness Scotland, UK
Date of Manufacture: 1982 Aug Date Code: 2J
Original Value: GB £6.62 (1985)
References: 1) Thorn Lighting Comprehensive Catalogue, 1983 UK, p.257
2) Thorn Lighting Comprehensive Price List, 1985 UK, p.60
3) Thorn EMI Merthyr Tydfil Specification MT11-TL-200 - Design Control Parameters IR Lamps - 7-VII-1988
4) Thorn EMI Merthyr Tydfil Specification MT11-ML-200 - Finishing Materials IR Lamps - 7-VII-1988
5) Thorn Lighting Kent Street Specification 11-2125A - Product Data 125mm Reflector Lamps - 24-VII-1987