Philips SDW-AR White SON Crown Silver
In 1986 Philips launched the SDW-T White Sodium lamps, having very high sodium vapour pressure around 95 kPa to realise a warm white light of 2500K with excellent colour rendering. The increased pressure required a hotter arc tube, and to avoid short life the seals were redesigned to the 'protruding plug' concept. The hot sodium reservoir and relatively cool seals to thin niobium-zirconium wires are separated from each other by long and thick-walled ceramic extension pieces. The arc tube is filled to high xenon pressure to maximise efficacy. Ignition is facilitated with a coiled tungsten antenna, supported on a moving bi-metal strip to prevent sodium loss while hot.

It was originally envisaged that White SON would replace incandescent lamps for high-end accent and display lighting applications, consuming about a third of the power. As such the early samples were prototyped in similar glass bulbs as incandescent lamps - such as this crown silver version and a blown reflector type. These were extensively trialled in shop lighting environments, but were never launched for sale.

This lamp is a replica which is similar to the originals, but its arc tube is extracted from a 35W SDW-T lamp and is not optimised for the heat reflection from the mirrored bulb, which varies significantly depending on the precise position of the arc tube. This is not well controlled with ordinary GLS lampmaking techniques but is critical for SDW lamps, and is maybe one reason why reflector types were never launched for sale. The final production tubular versions were equipped with a precision-focussed cap to reduce this problem. As the power curves show, this lamp must be operated at reduced power of around 22W to deliver the White SON spectrum.
Manufacturer: Philips (arc tube) J.D. Hooker (outer bulb)
Lamp Power: 22 Watts
Lamp Current: 0.28 Amps
Lamp Voltage: 102 Volts
Cap Type: E27/27 Ni plated brass + Vitrite
Bulb Type: PS-60 PS-19 in eighths/inch
Bulb Finish: Aluminised Crown Soda-lime glass
Electrodes: Tungsten-rhenium rod No emitter
Arc Length: 17 mm 21/32 inch
Atmosphere: Inner: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 550 ℓm
Luminous Efficacy: 27.5 ℓm/W
Colour Temperature & CRI: CCT: 2500K CRI: Ra 80
Chromaticity Co-ordinates: CCx: 0.479 CCy: 0.417
Rated Lifetime: N/A
Warm-up & Re-strike Time: 5 minutes 30 minutes max.
Burning Position: Universal
Overall Length: 104.5 mm 41/8 inches
Light Centre Length: 70 mm 23/4 inches
Factory: Turnhout, Belgium (arc tube) J.Hooker, Belgium (outer)
Date of Manufacture: 1987 (arc tube) 2018 (outer)
Original Value: N/A
 
References: 1) Photoelectric Measurement
2) Philips SDW-AR 35W lamp of Maxime Gendre at Lighting-Gallery.net
3) Philips SDW-AR 35W test of Maxime Gendre at Lighting-Gallery.net
4) The High Pressure Sodium Lamp, J.J de Groot & J.A.J.M. van Vliet, publ. Philips Technical Library 1985, p.256