Kolorarc MBI-T 250W Tri-Band Metal Halide
The Kolorarc MBI-T lamp was developed by Thorn Lighting as a high performance alternative to its standard Kolorarc range.  Its predecessors, the standard MBI range 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 the American and British-developed sodium-scandium lamps is their very high initial lumen output, but this is always followed by an exceptionally 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 metal halide lamp.  This delivered much more stable lumen output, but initial output was much lower and the colour stability rather poor - lamps tended to turn green during life owing to rapid sodium loss.

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.
Manufacturer: GE-Thorn Lamps Ltd.
Lamp Power: 250 Watts
Lamp Current: 3.0 Amps
Lamp Voltage: 105 Volts
Cap: E40s/45
Bulb Finish: Clear
Bulb Type: T-46
Overall Length: 220 mm
Focal Distance: 150 mm
Electrodes: Backwound thoriated tungsten
Atmosphere: Ar | Hg-In (Na, Tl, Hg)Ix Outer : Nitrogen
Luminous Flux (100 hrs): 21,000 lm @ 100 hours
Luminous Efficacy (100 hrs): 84 lm/W @ 100 hours
Colour Temperature & CRI: CCT: 4200K CRI: Ra 70
Chromaticity Co-ordinates: CCx: CCy:
Burning Position: Horizontal ±15°
Rated Life: 6000 hours to 70% survival
Warm Up / Re-strike Time: 2 minutes < 7 minutes
Factory: Leicester, England
Date of Manufacture: April 1991
Original / Present Value:
References: 1) GE Lighting UK Catalogue 1992.