Mazda MB/V High Pressure Mercury

This particular lamp represents one of the earliest styles of MB lamp made by the company. It employs a hand-made arc tube and the style of the packaging is a type which was phased out before 1950. The date code of 72 can therefore be translated into a manufacture date of December 1947.

The first mercury lamp placed on the market was the MA style having a hard glass arc tube and rated 400 Watts, but lamps of lower wattages soon became quite desirable. A 250W MA lamp was introduced and shortly after a 150W version arrived, but luminous efficacy fell sharply as lamp wattage was reduced. Lower wattage lamps need to operate at higher temperature and pressure to keep them efficient, and the special aluminosilicate glasses developed for the MA arc tubes were not sufficiently refractory.

Quartz has an even higher melting temperature, but it was not until methods has been found of chemically purifying it to lamp quality levels that it could be adopted. Even then, sealing metal wires through it was very difficult because quartz expands and contracts at a rate ten times slower than most metals. The answer lay in a thin strip of molybdenum foil, so thin that the quartz barely knows it's there, and having feathered knife-edges which can deform when the foil expands laterally. The seal was invented by D. Gabor, working with BTH and British Siemens at the time, and the 80W and 125W MB lamps were launched.

The hand-made arc tube has one seal at each end for the main electrodes, and a side-arm with a third seal for the auxiliary electrode. A 'pearl' GLS shaped bulb was necessary to diffuse the glare of the intensely bright MB arc tube.
Manufacturer: The British Thomson-Houston Co. Ltd.
Lamp Power: 80 Watts
Lamp Current: 0.8 Amps
Lamp Voltage: 115 Volts For 200-210V Mains
Cap Type: B22d-3/30x35 Brass + vitrite
Bulb Finish: Pearl Soda-lime soft glass
Bulb Type: PS-80 PS-25 in eighths/inch
Overall Length: 160 mm 6¼ inches
Light Centre Length: 120 mm 4¾ inches
Arc Length: 20mm ¾ inch
Electrodes: C-6 Open Coil Thoria pellet emitter
Atmosphere: Inner: Hg | Ar (8 atm) Outer: Nitrogen
Luminous Flux: 3,040 lm @ 100 hrs 2,240 lm @ 1500 hrs
Luminous Efficacy: 38.0 lm/W @ 100 hrs 28.0 lm/W @ 1500 hrs
Colour Temperature & CRI: CCT: 6000K CRI: Ra 16
Chromaticity Co-ordinates: CCx: 0.315 CCy: 0.380
Burning Position: Vertical cap up
Rated Lifetime: 1,500 hours Rated to 70% survival
Warm-up & Re-strike Time: 4 minutes 5 minutes
Factory: Rugby United Kingdom
Date of Manufacture: December 1947 Date Code: 72
Original & Present Value: £2 15s 0d (1947) £71.78 (2005)
References: 1) BTH-Mazda Lamp Catalogue, UK, 1947, p.23
2) Bourne, H.K., Discharge Lamps for Photography & Projection, Chapman & Hall, London, 1948