MBIF/H Lithium Doped Marks & Spencer Lamp
The 250W MBIF lamp from Thorn Lighting was the first HID lamp that achieved widespread success as a light source for retail spaces in Europe. One of the first users of these lamps was the British chain Marks & Spencer, who for many years had striven to simulate daylight conditions in the high quality clothing departments of their stores. Previously that task had always been accomplished with very large numbers of linear fluorescent lamps in oversized luminaires. The MBIF lamp offered the possibility to reduce the number of light points, but before accepting this light source, M&S noted that the output was slightly lacking in the red spectrum.

To win the contract and be first to establish metal halide as a lamp for retail interiors, Thorn developed a specially modified lamp exclusively for use in M&S stores.

The additional component of lithium iodide and an increased thorium content was employed to produce extra red light and raise the R9 red colour rendering index by a few crucial points. Thorium is well known for its capability to add red light to the spectrum of metal halide lamps, and this was the first use of lithium for the same purpose but in newly discovered proportions which do not negatively influence the lumen maintenance of the lamp. US Patent 4,247,298 was awarded to Thorn for the invention.

The mercury pressure in this arc tube is sufficiently low that the lithium radiation is not significantly broadened into the infrared spectrum which would otherwise lead to a reduction in luminous efficacy. To maintain high luminous efficacy, the usual red-emitting yttrium vanadate phosphor is combined here with blue emitting strontium chloroapatite.
Manufacturer: Thorn EMI
Lamp Power: 250 Watts
Lamp Current: 2.9 Amps
Lamp Voltage: 100 Volts
Cap: E40s/45 Ni plated brass
Bulb Finish: 45% Yttrium Vanadate, 55% Strontium Chloroapatite
Bulb Type: ED-90 Borosilicate
Overall Length: 183 mm
Light Centre Length: 110 mm
Electrodes: Backwound tungsten on thoriated shank
Inner / Outer Atmosphere: Inner: Ar | Hg (Na,Sc,Li)Ix Outer: Nitrogen
Luminous Flux: 19,000 lm (100 hours)
Luminous Efficacy: 76 lm/W (100 hours)
Colour Temperature & CRI: CCT: 3571K CRI: Ra=64
Chromaticity Co-ordinates: CCx: 0.420 CCy: 0.440
Burning Position: Horizontal
Rated Life: 6,000 hours to 70% survival
Warm Up / Re-strike Time: 3 minutes 8 minutes
Factory: Leicester England
Date of Manufacture: 31st May 1982 Date Code: 3105
Original / Present Value: Unknown
 
References: 1) US Patent 4,247,298.
2) Private communication with inventor of the M&S lamp.