MBIL/H Linear Metal Halide Floodlight

The MBIL lamp was a developed by Thorn's engineers Eric Beeson and Brian Page, as a floodlighting lamp based on earlier developments in long-arc UV metal halide photo-printing lamps of Sylvania.

The principal reason for the long arc was to enable the lamp to be used in floodlighting luminaires of a similar type to the very successful design which had been created for linear halogen lamps. There was a strong desire to achieve the same kind of optical control from a discharge lamp to realise their significant energy saving possibilities.

Prior to this time nearly all discharge lamps required an outer jacket to provide thermal insulation and prevent the end seals from oxidation. The large dimensions of the outer bulb made it impossible to locate such lamps at the focus of a small reflector, as was possible with linear halogen. From the outset of MBIL development it was decided to dispense with the outer jacket, thermal insulation and protection from the environment being provided by the sealed fitting it was designed to be used with.

The lamp is based on sodium-scandium chemistry. Early designs were made in clear quartz but owing to the long arc, colour inhomogeneities could occur due to demixing of the halides. Externally frosting the arc tube successfully resolved these issues. Special coloured lamps were also made for marine applications. Today the MBIL lamp continues to be popular in some applications on account of its remarkably good colour stability, but it has been largely superseded by shorter arc types which can achieve better efficacy in newly designed luminaires.
Manufacturer: Thorn Lighting Ltd. (Lamp No. 91-7473)
Lamp Power: 1500 Watts
Lamp Current: 6.7 Amps
Lamp Voltage: 250 Volts
Cap: Rx7s
Bulb Finish: Frosted quartz
Bulb Type: T-20.1 (pinches 21.3 wide)
Overall Length: 254 mm
Light Centre Length: 127 mm
Electrodes: Backwound tungsten with thoriated shank
Atmosphere: Ar | Hg (Na,Sc)Ix
Luminous Flux (100 hrs): 120,000lm (100hrs) 110,000lm (2000hrs)
Luminous Efficacy (100 hrs): 80 lm/W (100hrs) 73 lm/W (2000hrs)
Colour Temperature & CRI: CCT: 5200K CRI: Ra 65
Chromaticity Co-ordinates: CCx: 0.340 CCy: 0.360
Burning Position: Horizontal ± 45°
Rated Life: 6000 hours (to 50% survival)
Warm Up / Re-strike Time: 2 minutes 15-20 minutes
Factory: Leicester England
Date of Manufacture: July 1988
Original / Present Value: £88.00 (1988) £145.04 (2002)
References: 1) Thorn Lighting Comprehensive Catalogue, UK, 1989/90, p.366
2) Thorn Lighting Data Sheet 91-7473
3) Thorn UK Price List, 7th November 1988