|
Mazda SO/H Sodium Vapour Discharge Tube |
For many years, the 85W lamp had been a particularly troublesome animal for BTH and AEI to manufacture reliably. A problem of all sodium lamps at the time was the adsorption of the argon component of the neon-argon gas filling, which is necessary to lower the ignition voltage. Being the longest lamp with a small diameter discharge tube, the 85W had the highest striking voltage and was the most sensitive to argon cleanup. All of the company's low wattage lamps were produced from hand-drawn glass tubing in the region of 13-15mm outside diameter, while the large 140W rating was made in 15-17mm glass. To combat the 85W problems, the glass tubing was sorted into batches with the narrowest 13-14mm diameter tubes being employed for the lower wattages, while the larger 14-15mm diameter was reserved for the 85W. The slightly reduced loading on the glass helped slow the rate of argon cleanup. Such practice was not necessary for competitors lamps whose soft glass tubes showed slower argon cleanup - but would often crack.
Following a discovery by the GEC that the introduction of trace amounts of xenon could reduce the rise in striking voltage, BTH and AEI also experimented with this technique. This lamp almost certainly employs some 0.05% xenon which was applied only for the difficult 85W size which really needed it, because the inclusion of xenon resulted in a loss of up to 12% lumens. As an additional measure to facilitate starting, from 1957 onwards the 85W lamps were coated with a moisture-repellent silicone coating.
| Manufacturer: | Associated Electrical Industries Ltd. | |
| Lamp Power: | 85 Watts | |
| Lamp Current: | 0.6 Amps | 0.54A Starting Current |
| Lamp Voltage: | 150-180 Volts | 450V ignition |
| Cap Type: | By22d | Porcelain |
| Bulb Type: | Inner: TU-14½ (TU-4½") | |
| Bulb Finish: | Inner: Borate Hard Glass | |
| Electrodes: | CCC-6 Transverse | Black W + BCT Emitter |
| Arc Length: | ||
| Atmosphere: | Na | Ne 99.2%, Ar 0.75%, Xe 0.05% (12 torr) | |
| Luminous Flux: | 6,205 lm (@ 100 hrs) | 5,100 lm (@ 4000 hrs) |
| Luminous Efficacy: | 73.0 lm/W (@ 100 hrs) | 60.0 lm/W (@ 4000 hrs) |
| Colour Temperature & CRI: | CCT: 1700K | CRI: Ra -44 |
| Chromaticity Co-ordinates: | CCx: 0.574 | CCy: 0.425 |
| Rated Lifetime: | 6,000 hours | Guaranteed to 4,000 hrs |
| Warm-up & Re-strike time: | 11 minutes | Instantaneous |
| Burning Position: | Horizontal +20° -5° | |
| Overall Length: | 425 mm | 16¾ inches |
| Light Centre Length: | 230 mm | 9 inches |
| Factory: | Leicester | England |
| Date of Manufacture: | February 1955 | Date Code 62 |
| Original Value: | GB £3 3s 0d | |
