Philips SDW-T High Pressure Sodium White SON
In the 1980's Philips directed much of its attention to the development of very high pressure sodium lamps to further enhance its colour rendering properties. The sodium pressure here is 95 kPa, much higher than the 10 kPa of standard SON but still less than atmospheric. Increased pressure requires an increase in the arc tube temperature, and a new kind of seal had to be developed. A niobium-zirconium wire penetrates a thick-walled PCA extension piece at each end of the arc tube, thus removing the seal to a lower temperature region.

To facilitate starting of the slimmer arc tube which requires a higher xenon pressure, a spiral of tungsten wire runs alongside it, this being physically removed by a bi-metal strip when hot to prevent sodium loss. The frame beside the arc tube is kinked purely to reduce its imaging effects in the beamA special electronic controller is required to precisely regulate lamp current. With a normal ballast colour variation is unacceptably wide, and with full electronic ballasts the squarewave output reduces the colour temperature of the lamp. A standard magnetic ballast is therefore employed in conjunction with an electronic starter and controller to deliver longer life, best colour stability, and the highest CCT.

The lamp shown here represents the first generation type, launched in 1986. Its CRI is an impressive Ra85 and the colour temperature is 2500K warm-white, while luminous efficacy is four times greater than the incandescent display lamps it was designed to replace. The lamp was marketed in ratings of 35W, 50W and 100W, and all employ plastic pre-focussed caps designed to exactly locate the small arc tube in the optical system. Metal caps were introduced around 1995 because these plastic types sometimes discoloured.
Manufacturer: Philips Lighting
Lamp Power: 53 Watts
Lamp Current: 0.76 Amps 1.5A Starting current
Lamp Voltage: 92 Volts 3.5-4.5kV Ignition
Cap Type: PG12-1 Polycarbonate
Bulb Finish: Clear Borosilicate glass
Bulb Type: T-31.5 T-10 in eighths/inch
Overall Length: 145 mm 5¾ inches
Light Centre Length: 91 mm 3½ inches
Arc Length: 17 mm 21/32 inch
Electrodes: Tungsten-rhenium rod No emitter
Atmosphere: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 2,300 lm @ 100 hrs 2,070 lm @ 5,000 hrs
Luminous Efficacy: 43.4 lm/W @ 100 hrs 39.1 lm/W @ 3,000 hrs
Colour Temperature & CRI: CCT: 2500K CRI: Ra 85
Chromaticity Co-ordinates: CCx: 0.479 CCy: 0.417
Burning Position: Universal
Rated Lifetime: 5,000 hours to 50% survival
Warm-up & Re-strike Time: 5 minutes 30 minutes max.
Factory: Turnhout Belgium
Date of Manufacture: April 1991 Date Code 1H
Original & Present Value: £53.89 (1995) £69.40 (2005)
 
References: 1) Philips White SON Guide for Luminaire Manufacturers, June 1990.
2) Philips UK Price List December 1995.