Philips SOX-Plus Extended Life Lamp

The improved reliability SOX-Plus lamp was launched by Philips in 1993, with its goal being to extend the group re-lamping interval for low pressure sodium installations from two to three years such that they could benefit from the same long-life as high pressure sodium systems. The technical improvement lies in the electrode assembly.

Traditional SOX lamps suffer a weakness at the glass-to-metal seals. These are normally made to unborated dumet wire sleeved in 2-ply soda-lime glass having an external borate layer. Since the borate does not extend over the end of the glass bead to the encapsulated leadwire, that weak spot is protected by embedding a small tube of magnesia into the glass to keep away sodium, but it is only partly successful. Cracking of the seals due to sodium attack affects a small percentage of lamps. Gas leakage between the core and sheath of dumet is another rare failure mechanism. In 1986 Philips introduced the so-called 'SR' Sodium-Resistant electrode assembly, which was initially applied only for its Belgian-made SOX-E range. It replaced the dumet seal with a single piece leadwire of 'Vacovit' iron-nickel-chromium alloy, sleeved with a single layer of pure borate glass. No ceramic bead is necessary. Elimination of premature seal failures leads to a small improvement in life.

Even though the SOX-Plus life claims showed a significant improvement, the actual gain was minimal as traditional lamps had been out-performing their life claim for several years. Rather than updating those claims to reflect reality, Philips cunningly developed the parallel range of SOX-Plus lamps, identifiable by their red caps, and increased profits by selling these new 'long life' lamps at higher prices.
Manufacturer: Philips Lighting Ltd.
Lamp Power: 35 Watts
Lamp Current: 0.60 Amps
Lamp Voltage: 70 Volts
Cap Type: BY22d Red Alkyde Insulator
Bulb Type: T-50 T-16 in eighths/inch
Bulb Finish: Indium-tin oxide film Soda-lime glass
Electrodes: CCC-4 Beehive Black W + BCT emitter
Arc Length:
Atmosphere: Na | 99% Ne, 1% Ar Outer: Hard Vacuum
Luminous Flux: 4,550lm (@ 100 hrs)
Luminous Efficacy: 130.0 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 1700K CRI: Ra -44
Chromaticity Co-ordinates: CCx: 0.574 CCy: 0.425
Rated Lifetime: 12,000h (85% survival) 20,000h (50% survival)
Warm-up & Re-strike time: 11½ minutes Instantaneous
Burning Position: Vertical Cap Up ± 110°
Overall Length: 310 mm 12¼ inches
Light Centre Length: 183 mm 7¼ inches
Factory: Hamilton Scotland
Date of Manufacture: January 1996 Date Code 6A
Original / Present Value: GB £36.03 (1995) GB £61.86 (2014)
References: 1) Riley, D., 1993. SOX-Plus Saves You £'s. 'The Lighting Journal' of the UK Institution of Lighting Engineers, June 1993 p.129.
2) Warner, P., 1995. Report of SOX-Development Conference. 'The Lighting Journal' of the UK Institution of Lighting Engineers, June 1993 pp.190-191.
3) Sprengers, L.M. & Peeters, J.I.C., 1986. SOX-E - A New Generation of LPS Lamps. Journal of UK National Lighting Confererence 1986, pp.266-272.
4) Philips UK Lamp Catalogue 1997/98.
5) Philips UK Price List December 1995.