Mazda MAF/V Mercury Fluorescent

The MAF lamp marked the first application of a phosphor to the outer bulb of a mercury lamp, in an effort to improve its colour rendering. The original concept was pioneered by Osram-GEC in 1937. By 1938 BTH-Mazda followed with this lamp, which differs mainly in the shape of its outer bulb.

The luminescent material is zinc cadmium sulphide activated by copper, (Zn,Cd)S:Cu. It is stimulated by the 365nm UV-A that is able to pass through the hard glass inner arc tube, and produces a weak orange radiation which boosts the red ratio of the lamp from 1% to about 4%. Since the phosphor loses its efficiency above about 150°C, MAF lamps employ a large bulb. This has an isothermal shape to maintain a low surface temperature when operated in the cap-up position.

One drawback of this phosphor is its yellow body colour, which absorbs the violet and blue mercury lines. Despite its own orange radiation and notable improvement in colour rendition, the net result is a rather unpleasant greenish light. This was partly overcome by adding cadmium to the arc, which produces extra blue light. This helps achieve a whiter appearance, but the colour still leaves a lot to be desired and reduces efficacy - 12% drop was claimed, but testing shows 30% less. Cadmium also has a lower vapour pressure than mercury, and to bring it into the plasma the lower end of the arc tube is tapered to increase its temperature.

BTH also made a tubular MAF lamp to fit smaller luminaires, but the phosphor had little benefit due to its hot operation and it was dropped by the early 1940s. At that time the neck of this lamp was lengthened to improve compatibility, and it was produced without further changes until around 1959.
Manufacturer: The British Thomson-Houston Co. Ltd.
Lamp Power: 400 Watts
Lamp Current: 3.0 Amps 5.0A during starting
Lamp Voltage: 145 Volts For 220-230V Mains
Cap Type: E40s/45 Brass + porcelain
Bulb Type: ED-165 ED-56 in eighths/inch
Bulb Finish: Zinc Cadmium Sulphide (Zn,Cd)S:Cu
Electrodes: C-6 Open Coil Thoria pellet emitter
Arc Length: 160mm 6¼ inches
Atmosphere: Inner: HgCd | Ar (1 atm) Outer: Nitrogen
Luminous Flux: 15,200 lm claimed 11,100 lm measured
Luminous Efficacy: 38.0 lm/W claimed 27.8 lm/W measured
Colour Temperature & CRI: CCT: 5200K CRI: Ra 40
Chromaticity Co-ordinates: CCx: 0.325 CCy: 0.430
Lifetime: 5000 hours
Warm-up & Re-strike Time: 5 minutes 10 minutes
Burning Position: Vertical cap up
Overall Length: 335 ± 7.5 mm 13¼ inches
Light Centre Length: 195 ± 7.5 mm 7½ inches
Factory: Rugby England
Date of Manufacture: December 1945 Date Code: 48
Original Value: £3 12s 6d (1947)
References: 1) BTH-Mazda Lamp Catalogue, UK, 1937, pp.23 & 50 - first known listing of MAF/V isothermal and tubular lamps.
2) BTH-Mazda Lamp Catalogue, UK, 1941, pp.29 & 52 - photographs and further details of MAF/V isothermal and tubular lamps.
3) BTH-Mazda Lamp Catalogue, UK, 1947, pp.24 & 38 - technical data for this lamp, with longer neck to replace the earlier tubular version.
4) BTH-Mazda Lamp Catalogue, UK, 1947, pp.39, 43, 46 - photograph of this lamp with longer neck
5) BTH-Mazda Lamp Catalogue, UK, 1954, pp.37, 41, 44 - last mainstream listing of MAF. Introduction of new support frame illustrated.
6) BTH-Mazda Lamp Catalogue, UK, 1955, pp.22-23 - MAF/V lamps delisted and replaced by MBF - at more than double the price!
7) AEI-Mazda Lamp Catalogue, UK, 1957, pp.24-25 - MAF/V lamps re-listed - presumably due to high cost difference vs quartz MBF
8) AEI-Mazda Lamp Catalogue, UK, 1959, pp.28-29 - final known listing of MAF/V lamps
9) AEI-Mazda Datasheet, MA Mercury Lamps, UK, 1958 - technical data for this lamp
10) Electric Lamps, ELMA Lighting Service Bureau, 1949, pp.83-85
11) Electric Discharge Lamps, H. Cotton, publ. Chapman & Hall 1946, pp.354-358
12) Discharge Lamps for Photography and Projection, H.K. Bourne, publ. Chapman & Hall 1948, pp.88-91
13) Lamp photometric measurement in integrating sphere and on spectroradiometer