Mazda MA/U Medium Pressure Mercury
Represented here is the later style of MA production from the Mazda company, which was operated by AEI Lamp & Lighting Co. at this time. The lamp has been considerably improved from earlier designs in the BTH days, most noticeable being the improved arc tube frame mount. The former frame often resulted in breakage of the arc tube and was particularly time consuming to manufacture. Use is made of stamped steel plates here which are sprung-loaded onto the arc tube ends and these offered a far better degree of cushioning against impact while also speeding production. Dating this lamp to the time of AEI's 1955 takeover of BTH is simple because of the fact that the packaging makes use of BTH material with AEI labels affixed over them.

It is interesting to note that this lamp also has an individual serial number etched into the arc tube, specifying the glass batch which was employed. The lettering C46 refers to the glass type (later known as A42 after the AEI and GEC glassworks merged), which had recently been introduced to replace the slightly softer C37 (A431) grade. C46 was a harder aluminosilicate glass made by BTH Chesterfield, and its introduction permitted a slight increase in luminous flux.

Seals at either end of the hand-blown glass arc tube are made to glazed molybdenum rods, each of which supports the main electrode on a moly T-piece. The main open-coled tungsten electrodes contain an emissive pellet of radioactive thorium oxide to facilitate starting and maintain efficient operation of the lamp. For heat retention purposes, a layer of platinum paint has been applied to the area of the arc tube immediately behind each electrode, and the threads of the cap have been lubricated with a graphite coating.
Manufacturer: Associated Electrical Industries Ltd.
Lamp Power: 250 Watts
Lamp Current: 2.15 Amps
Lamp Voltage: 145 Volts For 200/250V Mains
Cap Type: E40s/45 Brass + Vitrite
Bulb Finish: Clear Borosilicate hard glass
Bulb Type: T-51 T-16 in eighths/inch
Overall Length: 290 mm 11½ inches
Light Centre Length: 170 mm 6¾ inches
Arc Length: 120mm 4¾ inches
Electrodes: C-6 Open Coil Thoria pellet emitter
Atmosphere: Inner: Hg | Ar (1 atm) Outer: Nitrogen
Luminous Flux: 8,250 lm VBU mean 7,500 lm HOR mean
Luminous Efficacy: 33.0 lm/W VBU mean 30.0 lm/W HOR mean
Colour Temperature & CRI: CCT: 5400K CRI: Ra 6
Chromaticity Co-ordinates: CCx: 0.337 CCy: 0.421
Burning Position: Universal H lumens = V less 10%
Rated Lifetime: 6,000 hours (to 50% survival)
Warm-up & Re-strike Time: 7 minutes 7 minutes
Factory: Leicester England
Date of Manufacture: March 1955 Date Code: 74
Original & Present Value: £2 17s 6d (1954) £52.75 (2005)
 
References: 1) BTH-Mazda Lamp Catalogue, UK, 1955, p.21
2) AEI Mazda Lamp Data Sheet 1/DIS/MA/1 September 1958