Mazda MB/U High Pressure Mercury

This lamp represents the last style of mercury lamp production in bulbs which were not coated with colour-correcting phosphor. The MBF coated lamp had taken over the vast majority of the mercury lamp market, but in certain environments the user had no concern for good colour rendering and preferred the more economically priced uncoated lamps.

This particular lamp was made along exactly the same lines as the mercury fluorescent products, even making use of the isothermal elliptical bulb shape which was required to keep the phosphor at a uniform temperature around the arc tube. The bulb is inside frosted to give it the pearl appearance, as this was always necessary in low wattage MB lamps to diffuse the glare of the intensely bright arc tube.

It is interesting to note the remarkably high level of quality to which the Mazda lamps were assembled, particularly in terms of their mechanical strength. Most HID lamps have their arc tubes supported on a simple wire frame, sometimes with an auxiliary support at the upper end of the bulb. The Mazda style instead made use of the 'Flare Strap' mounting style. A heavy-guage nickel-manganese wire was mechanically clamped to the side of the glass flare tube with a welded nickel strip, a thin spacer of mica in between relieving stress on the glass. The arc tube is welded to the frame wire with nickel straps and in this way, no stresses were placed on the electrical welds carrying current to the arc tube. Competitors lamps supported the arc tube on the current-carrying wires themselves and vibration damage etc frequently damaged the spot welds and caused total failure of the lamp.
Manufacturer: AEI Lamp and Lighting Co. Ltd.
Lamp Power: 125 Watts
Lamp Current: 1.15 Amps
Lamp Voltage: 125 Volts For 220-250V Mains
Cap Type: B22d-3/25x26 Ni plated brass + vitrite
Bulb Finish: Pearl Soda-lime soft glass
Bulb Type: E-75 E-23½ in eighths/inch
Overall Length: 183 mm 7¼ inches
Light Centre Length: 110 mm 4 3/8 inches
Arc Length: 25mm 1 inch
Electrodes: Backwound tungsten Double carbonate emitter
Atmosphere: Inner: Hg | Ar (8 atm) Outer: Nitrogen
Luminous Flux: 4,900 lm average through life
Luminous Efficacy: 39.2 lm/W average through life
Colour Temperature & CRI: CCT: 6000K CRI: Ra 16
Chromaticity Co-ordinates: CCx: 0.315 CCy: 0.380
Burning Position: Universal Horiz. lumens 10% less
Rated Lifetime: 7,500 hours Rated to 70% survival
Warm-up & Re-strike Time: 4 minutes 5 minutes
Factory: Leicester England
Date of Manufacture: June 1969 Date Code: 42
Original & Present Value: £2 3s 9d (1969) £23.69 (2005)
References: 1) Thorn Lighting Comprehensive Catalogue, UK, 1969/70, p.CF5