The Graph-X is a high wattage ultra-violet reflector lamp, created by Thorn Electrical Industries in the late 1960's. It was developed following a programme of experimentation to determine which metal halide salts would be of most use for the creation of improved metal halide lamps, and some of these materials were found to deliver a spectral output that was suited to lamps for non-lighting applications.

This lamp is based on the iodides of gallium and iron which together, radiate strongly in the blue and UV-A regions of the spectrum. A wide band of radiation between 315nm and 420nm is emitted which makes its output particularly suited to the fields of photo-printing, graphic arts, photo-resists, diazo photopolymer reproduction and other materis. The stippled front lens acts as a most effective spreader, homogenising the light and giving an elliptical beam distribution measuring approximately 24" x 36" at a distance of 2/3 feet infront of the lamp.

It is intended for operation at either 400 or 800 Watts. Lamp life is quite short and electricity consumption rather high at full power, and the lamp takes a minute or so to run up to this level. A system was developed which simmers the lamp at 400W, and when switched to the higher power the response in output is immediate, thus saving electricity and lamp life.