||The Kolorarc MBI-T lamp was developed by Thorn engineer Ken Brown as a high performance alternative to its standard Kolorarc range. The earlier lamps were are based on sodium-scandium technology which had been developed through Thorn's close links with Sylvania of USA. In effect, the Thorn MBI lamps are simply versions of the Sylvania originals which have been tailored to suit European ballasts.
A characteristic feature of American and British-developed sodium-scandium lamps is their high initial lumen output, but this is always followed by rapid lumen depreciation. Consequently in later life they are not nearly so efficient. However they have the advantage that their spectral output remains fairly constant, and strong colour shifts are unusual. The competitive technology being developed in Europe by Philips was the tri-band sodium-indium-thallium chemistry. This delivered more stable lumen output, but initial output was lower and the colour stability from lamp-to-lamp, as well as colour rendering quality, was rather poor.
This lamp was Thorn's attempt to develop a new lamp having the advantages of both technologies. It features a shaped arc tube having end seals of very small cross-section, which minimise thermal losses and ensure higher cold spot temperatures and good luminous efficacy, but without overheating the central portion of the arc tube so that sodium loss would be accelerated. A steatite ceramic insulator over the side frame further enhances colour stability by slowing sodium loss. Ignition of the lamp is assisted by a small UV-enhancer which produces a brief pulse of UV radiation, these high energy photons then ionising the gas in the arc tube.