Philips SO/H 45W of British Design
Despite the fact that the low pressure sodium lamp is of European origin, it quickly became a distinctly British light source and gained considerable popularity in that country. Soon after Philips' invention of the lamp in the Netherlands, the British manufacturers BTH-Mazda and Osram-GEC established their own production in England. Even though they were not the pioneers of this lamp technology, they dominated the British market due to the strong preferences for buying locally-made products. It was clear to Philips that if it was to gain a foothold in this most important market, it would have to set up a duplicate of its production in that country.

The first British-made Philips sodium lamps appeared in the 1940s, and were presumably built at the Philips incandescent lamp factory in Harlesden, London. Being discharge devices however, they could have instead been produced at the company's valve and CRT plants in Croydon or Blackburn. In 1949 all lampmaking was transferred to a new factory at Hamilton in Scotland, and it is believed that this lamp would have been produced there.

Unsurprisingly, the design of this lamp appears identical to its Dutch counterparts of the same era. Later however, Philips Eindhoven made a number of improvements to its SO/H lamps. In 1955 the Dutch lamps were superseded with an improved type having a Bamboo-shaped discharge tube, and in 1958 these were replaced again with a lamp having sodium-retention dimples. The British factory lagged behind and did not produce either of those versions in the SO/H format, and continued producing the original design illustrated here right up to the mid 1960s.
Manufacturer: Philips Lighting Ltd.
Lamp Power: 45 Watts
Lamp Current: 0.6 Amps 0.54A Starting Current
Lamp Voltage: 65-90 Volts 450V ignition
Cap Type: By22d Porcelain
Bulb Type: Inner: TU-14 (TU-4½") Dewar: TA-50 (TA-16")
Bulb Finish: Inner: Borate Soft Glass Dewar: Clear Soft Glass
Electrodes: CCC-4 Beehive BCT emitter
Arc Length:
Atmosphere: Inner: Na | NeAr Dewar: Vacuum
Luminous Flux: 2,700 lm (@ 100hrs) 2,200 lm (average)
Luminous Efficacy: 60 lm/W (@ 100hrs)
Colour Temperature & CRI: CCT: 1700K CRI: Ra -44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Rated Lifetime: 6,000 hours 50% survival, 60% flux
Warm-up & Re-strike time: 11 minutes Instantaneous
Burning Position: Vertical Cap Up ±95°
Overall Length: 238 mm 9 3/3 inches
Light Centre Length: 140 mm 5½ inches
Factory: Hamilton Scotland
Date of Manufacture: Inner: February 1952 Dewar: May 1951
Original / Present Value: £5 7s 6d (1953) GB£80.12 (2014)
 
References: 1) Philips Lighting UK Catalogue, 1953