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On 6th March 1961 Sylvania made history with the launch of this lamp, the world's first to feature a cool-beam dichroic reflector. Cold light coatings were pioneered several years earlier by Bausch & Lomb, to reduce the heat from carbon arcs in 35mm cinema film projectors. B&L offered its new technology to GE, which ridiculed the idea of a dichroic lamp due to the high costs. It therefore approached Sylvania, which immediately saw the potential and developed a manufacturing technique to minimise the cost impact. This was based on the sagging process, in which a thin glass sheet is heated and allowed to slump into a mould to produce an ellipsoidal reflector with excellent surface quality.
The first lamp is believed to be this ANSI-coded DLS model, based on the earlier DLG of similar design with aluminium reflector. A multilayer dichroic coating of magnesium fluoride and zinc sulphide reflects visible light forward while infrared is transmitted backwards, reducing heat in the beam by 50%. This allowed the brightness of projected movies to be greatly increased, without risk of overheating the film. Image sharpness was also improved by limiting expansion as the film passed through the heat at the projection gate. Another advantage was a small spectral shift, achieving a whiter light with the appearance of being brighter.
The dichroic lamp triggered a new era in 8mm projectors, and was quickly followed by the 250W DLR for 16mm film. It proved so popular that GE was forced to copy the design, introducing its 'Dikor' DEF in 1962. Sylvania maintained its lead by adapting the dichroic reflector into the bulb envelope for its Tru-Beam DNF and Halogen Super Tru-Beam, whose invention led to the ubiquitous MR16 dichroic lamps. |