MBI-T 400W Indium Iodide Blue Lamp

Osram-GEC was relatively late to enter the market for general lighting metal halide lamps, principally owing to the fact that it appeared to have had difficulty in making lamps having a high quality white light output that was stable throughout lamp life.

GEC metal halide lamps were based on tri-band technology, consisting essentially of a normal 400W mercury arc tube dosed with the halides of sodium (peach colour), thallium (green) and indium (blue). By adding these constituents in the appropriate quantities it was possible to balance their respective radiations to yield a white light output. However the sodium iodide was lost relatively quickly in the early GEC lamps as a result of electrolysis effects and reactions with other arc tube materials which saw it gradually being consumed. Consequently the colour would shift either towards blue or green as the relative intensity of the remaining indium or thallium dose took over the discharge.

Since it proved so difficult to make a stable white lamp, but very easy to make one whose colour ended up strongly coloured blue or green, it was decided to try marketing these lamps in coloured versions, with some success. They proved popular for the floodlighting of trees in parks and gardens in inner-city areas, or to produce spectacular effects in the night lighting of prestigious buildings.

Both the blue and green 400W lamps incorporate a snap-starter allowing the lamps to be operated from a normal mercury lamp ballast. However the use of an electronic 'stabiliser' was recommended to control the shape of the current waveform and prevent both flicker, and overloading of the electrodes which would lead to premature blackening.
Manufacturer: The General Electric Company of England PLC
Lamp Power: 400 Watts
Lamp Current: 3.6 Amps 5.5A during starting
Lamp Voltage: 120 Volts
Cap: E40s/45 nickel plated brass
Bulb Finish: Clear borosilicate
Bulb Type: T-51
Overall Length: 285 mm
Light Centre Length: 177 mm
Electrodes: Backwound tungsten
Inner / Outer Atmosphere: Inner: Ar | Hg, InBr Outer: Hard Vacuum
Luminous Flux: 8,000 lm (100 hours) 6,000 lm (2000 hours)
Luminous Efficacy: 20 lm/W (100 hours) 15 lm/W (2000 hours)
Colour Temperature & CRI: CCT: N/A CRI: Ra=0
Chromaticity Coordinates: CCx: 0.200 CCy: 0.140
Burning Position: Vertical cap up to cap 20 below horizontal
Rated Life: 2000 hours useful life
Warm Up / Re-strike Time: 2 mins. to 80% lumens 10-15 minutes
Factory: Shaw, Oldham England
Date of Manufacture: September 1986
Original / Present Value: GB £60.69 (1988) GB £100.03 (2002)
References: 1) Osram-GEC Lamp Catalogue, UK, 1985/86, p.212
2) Osram-GEC Price List 1988