Thorn Graph-X Universal Photoprinting Lamp

In the early 1970s Thorn became one of the first companies to introduce metal halide lamps for photochemical reactions, following the research led by Eric Beeson. Previously such actinic radiation had been produced by mercury lamps which offered high output, but their radiation was inconveniently concentrated in narrow spectral lines at 365 and 401nm. Alternatively carbon arcs were used, whose electrodes could be doped with metallic additives to produce broad UV-A and deep blue wavelengths ideally suited to diazo photopolymer materials, but were unstable and needed constant attention. Metal halide lamps allowed the introduction these species into an arc tube, solving both problems to create actinic radiation sources of both long life and high performance.

One of the first lamps was Thorn's Gallium Halide 1200W MBIL, introduced around 1970 for Agfa-Gevaert colour proofing units. In 1972 Thorn added the innovative Graph-X lamp, featuring a sealead beam reflector. Its superior optical efficiency allowed this small 400W lamp to match systems of 3-4x higher power, and the textured glass lens producing an elliptical beam suitable for exposing a 24x36" area from a distance of 3'. The nitrogen atmosphere in the reflector also extended life. By the mid 1970s it was re-named Graph-X 417 and joined by the iron halide Graph-X 365, optimised for materials sensitive to 365nm. Both were subsequently re-rated to allow boosting to 800W at the moment of exposure, while normally simmering at the original 400W rating.

In 1983/84 both lamps were replaced again by this Graph-X Universal, comprising gallium and iron halides in a single lamp to produce broad radiation from 315-450nm. Most recently it was upgraded to allow boosting up to 1000W.
Manufacturer: GE-Thorn Lamps Ltd.
Lamp Power: 400 / 1000 Watts
Lamp Current: 4.6 Amps @ 400W 8.7 Amps @ 800W
Lamp Voltage: 95 Volts @ 400W 100 Volts @ 800W
Cap: Spade terminals
Bulb Finish: Half Aluminised Borosilicate
Bulb Type: PAR-64 (202 mm)
Overall Length: 110 mm
Light Centre Length: Arc tube 10mm behind seating plane of reflector
Electrodes: Backwound thoriated
Atmosphere: Inner: Ar | Hg (Ga,Fe)Ix Outer: Nitrogen
Luminous Flux:
Luminous Efficacy:
Colour Temperature & CRI: CCT: CRI:
Chromaticity Co-ordinates: CCx: CCy:
Burning Position: Universal
Rated Life: 1000hrs @ 400W 400hrs @ 800W
Warm Up / Re-strike Time 1000W:1min/800W:2min 7-10mins/2-3mins if cooled
Factory: Leicester England
Date of Manufacture: February 1993 Date Code: 38
Original / Present Value:
References: 1) Thorn Lighting Comprehensive Catalogue, UK, 1984/85, p.233