Philips SO/H Sodium Vapour with Dewar Jacket
Almost from the outset Philips operated two sodium vapour lamp factories, the first of which was located in Eindhoven, The Netherlands.  A second British factory was based at Hamilton in Scotland and that is where this particular lamp was manufactured.  The Eindhoven production was relocated to Turnhout in Belgium many years later, but today all low pressure sodium lamp production is centred in Hamilton.

This lamp has seen a considerable amount of use, as evidenced by the brown staining of the discharge tube caused by sodium attack on this early glass type.  It is still fully functional, although the stained glass has naturally reduced the luminous flux of this lamp by a considerable amount.  The Philips trade-mark dimples blown in the sides of the discharge tube are not present on this lamp, which suggests that it is of later manufacture.  The dimples were originally present, but were later removed from SO lamps and employed only on the integral SOI design, because it was found that on bare SO arc tubes, they were too easy to break accidentally when inserting an inner into the dewar.

Even on this early example, it is interesting to note the excellent glassworking quality achieved by Philips.  Lamps from this company are today characterised by a remarkable degree of uniformity of glass wall thickness around the U-bend (see close-up photo) , whereas competitor's bends tend to thicken on the inside which can lead to the glass cracking here.  The pinch-seals around the electrodes are perfectly shaped, and the discharge tube exhaust tip-off has been hand-formed to a very desirable shape to give trouble-free service.  Despite being British made, it is likely that the glass here is of Dutch origin.
Manufacturer: Philips Electrical Industries Ltd.
Lamp Power: 45 Watts
Lamp Current: 0.60 Amps 0.54A Starting current
Lamp Voltage: 65-90 Volts 200-250V Mains voltage
Cap Type: BY22d Porcelain Small
Bulb Finish: Clear Soft glass arc tube
Bulb Type: Inner: TU-14½ x 32 Outer: TA-50
Overall Length: 238 mm 9 3/8 inches
Light Centre Length: 140 mm 5½ inches
Arc Length:
Electrodes: CCC-4 Triple Coil Black W + BCT Emitter
Atmosphere: Na | Ne 98.5% Ar 1.5% Outer: Vacuum
Luminous Flux: 2,700 lm (@ 100 hrs) 2,300 lm (mean to 4000hrs)
Luminous Efficacy: 60.0 lm/W (@ 100 hrs) 48.9 lm/W (mean to 4000hrs)
Colour Temperature & CRI: CCT: 1700K CRI: Ra-44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Burning Position: Vertical Base Up ± 95°
Rated Lifetime: 6,000 hours
Warm-up & Re-strike Time: 11 minutes Instantaneous
Factory: Hamilton Scotland
Date of Manufacture: Inner: January 1954 Dewar: September 1954
Original & Present Value: £3 4s 3d (1953) £60.00 (2005)
 
References: 1) Philips UK Lamp Catalogue, 1953.