Thorn Compact Iodide Daylight CID Lamp
The CSI and CID compact source lamps from Thorn Lighting proved extremely popular in the professional studio lighting business during the 1970s and 1980s, primarily on account of their very compact dimensions by comparison with the alternative state of the art.  Such types of compact source lamp were traditionally always made in the double ended format, which resulted in large lamps that were not so easy to mount in an optical system.

Thorn, or rather its predecessor AEI-Mazda, was responsible for developing the first single ended metal halide arc tubes with only one pinch-seal.  The first lamp in the family was the 400W Compact Source Iodide (CSI) , developed primarily as a technical light source for special projection.  A 1000W version soon followed, which was widely employed in floodlighting applications.  A very narrow and tightly controlled beam was attainable on account of the small arc and the ease with which it could be mounted in a reflector.

A later development was the Compact Iodide Daylight CID lamp in 575W and 1000W.  These competed with the double ended HMI and MEI types of Osram, delivering a similarly high daylight colour temperature.  Colour rendering suffered slightly owing to Thorn's preference for the indium-tin halide system, which was inferior to the Osram rare earth system.

This 2500W lamp is the largest in the family, and its G38 base and light centre length is the same as that of the 5000W and compact 10,000W studio halogen lamps, thus enabling simple retrofitting into standard lanterns.  Insulation between the lead wires is effected with several plates of mica inserted between the lead wires into a slit in the pinch.
Manufacturer: Thorn Lighting Ltd.  (Lamp Ref. 99-0431)
Lamp Power: 2500 Watts
Lamp Current: 30 Amps
Lamp Voltage: 100 Volts
Cap: G38
Bulb Finish: Clear
Bulb Type: G-40
Overall Length: 175 mm max.
Light Centre Length: 127 ± 2 mm
Electrodes: Backwound tungsten, 18mm arc length
Atmosphere: Pure Argon
Luminous Flux: 200,000 lm
Luminous Efficacy: 80 lm/W
Colour Temperature & CRI: CCT : 5500K  CRI : Ra 85
Chromaticity Co-ordinates: CCx : 0.333 CCy : 0.341
Rated Life: 350 hours
Factory: Leicester, England
Date of Manufacture: August 1983
Original / Present Value: £415.03 (1988) £672.72 (2001)