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Osram MAF/V Mercury Fluorescent |
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 its efficiency for converting the UV into reddish-orange light. The special shape of the bulb has an isothermal profile, and when the lamp is operated in the cap up position, the phosphor temperature is maintained in the region 100-150°C.
This phosphor has such a high cadmium content that it shows a natural yellowish body colouration. This quite strongly absorbs the usual 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, London | England |
| Date of Manufacture: | August 1952 | Date Code: 32 |
| Original & Present Value: | £3 12s 6d (1951) | £76.23 (2005) |
