Mazda SO/H Sodium Vapour Discharge Tube

This SO/H sodium vapour lamp was one of the first Mazda lamps to be manufactured after the parent BTH company had become Associated Electrical Industries, and features that company's unique hard glass 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
References: 1) BTH-Mazda Lamp Catalogue, UK, 1955, p.21