Osram MAF/V Mercury Fluorescent

This MAF lamp represents the first application of a phosphor coating to the outer jacket of a mercury lamp. It was developed in 1937 at the Wembley laboratories of Osram-GEC in London, where the modern medium pressure mercury lamps had been invented just a few years earlier.

The luminescent material is zinc cadmium sulphide with an impurity of copper as the activator (Zn,Cd) S:Cu. This type of coating is sensitive to the longwave UV radiation which is able to escape through the hard glass arc tube. The great size of this lamp is necessary to ensure that the temperature of the phosphor does not exceed 150°C, above which it loses efficiency in converting UV into reddish-orange light. The special shape of the bulb has an isothermal profile, and when perated in the cap up position, the phosphor temperature is maintained in the region 100-150°C.

The phosphor has such a high cadmium content that it shows a natural yellowish body colouration. This absorbs the mercury blue lines, and despite the extra red radiation, it makes the green mercury lines relatively more powerful. The colour hue of the MAF lamp was thus not always considered to be so desirable. The problem in this lamp is partially overcome by the addition of cadmium to the arctube, which radiates extra blue lines, and some weak red radiation. Luminous efficacy falls as a result, but the red ratio is valuably increased from around 1% to approximately 4%.

It is interesting to note the conical form of the arc tube at the lower end. This serves to raise the wall temperature in this region, and assists in keeping the additional cadmium metal dose fully vaporised into the discharge.
Manufacturer: The General Electric Company of England PLC
Lamp Power: 400 Watts
Lamp Current: 3.25 Amps 5.0A during starting
Lamp Voltage: 130 Volts For 220-230V Mains
Cap Type: E40s/45 Brass + porcelain
Bulb Finish: Zinc Cadmium Sulphide (Zn,Cd)S:Cu
Bulb Type: BT-165 BT-56 in eighths/inch
Overall Length: 335 ± 7.5 mm 13¼ inches
Light Centre Length: 190 ± 8 mm 7½ inches
Arc Length: 160mm 6¼ inches
Electrodes: C-6 Open Coil Thoria pellet emitter
Atmosphere: Inner: Hg | Ar (1 atm) Outer: Nitrogen
Luminous Flux: 15,250 lm (@ 100 hrs) 12,800 lm (average)
Luminous Efficacy: 38.1 lm/W (@ 100 hrs) 32.0 lm/W (average)
Colour Temperature & CRI: CCT: 4650K CRI: Ra 29
Chromaticity Co-ordinates: CCx: 0.365 CCy: 0.461
Burning Position: Vertical cap up
Rated Lifetime: Not published
Warm-up & Re-strike Time: 5 minutes 10 minutes
Factory: Hammersmith England
Date of Manufacture: August 1952 Date Code: 32
Original & Present Value: £3 12s 6d (1951) £76.23 (2005)
References: 1) Osram-GEC Lamp Catalogue, UK, 1951, p.35, relates to average through life lumen data.
2) Photometric lamp measurement relates to 100 hour lumen and colour data.
3) http://www.lamptech.co.uk/Documents/M14B Sulphide.htm.