Philips SON-T Comfort 250W
While the high efficacy and long life of the standard HPS lamp make it eminently suitable for exterior and industrial lighting, its relatively poor colour rendering excludes it from uses where better colour fidelity is required. Nevertheless in the 1980s it was not unusual to find ordinary HPS lamps in such applications as office or even shop window lighting, to achieve higher light levels at low cost. Naturally the results were quite unsatisfactory, and efforts began on improving the colour rendering properties of this light source.

The first such lamp from Philips was the SON-T Comfort in this 250W rating, launched around 1987. It employs the well-known principle that an increase in sodium vapour pressure results in the spectrum being further broadened, which leads to a higher colour rendering index. The vapour pressure of the sodium has been increased in this design by a combination of applying heat-reflectors of niobium around the arc tube in the area behind the electrodes, and reducing the arc length. Ordinarily such changes would result in a somewhat greenish colour light, so to bring the colour point back to the blackbody locus the mole fraction of sodium in the amalgam has been adjusted to about 80%.

High-loaded lamps of this type are especially susceptible to loss of sodium during life, which results in a change in the amalgam composition and the resulting light colour. To minimise this problem the diameter of the arc tube is larger than normal, and the electrodes are coated with a different emissive material which has a reduced rate of reaction with the sodium. To minimise efficacy loss, the xenon pressure in this lamp is higher than normal. Starting is facilitated with the aid of an auxiliary ignition antenna.
Manufacturer: NV Philips Gloielampenfabrieken
Lamp Power: 250 Watts
Lamp Current: 3.0 Amps
Lamp Voltage: 100 Volts 3500V ignition
Cap Type: E40s/45 Ni plated brass + vitrite
Bulb Type: T-46 T-14.5 in eighths/inch
Bulb Finish: Clear Borosilicate glass
Electrodes: Backwound Tungsten Ba3Y2WO9 emitter
Arc Length: 65 mm 2.5 inches
Atmosphere: Inner: Na,Hg|Xe Outer: Hard Vacuum
Luminous Flux: 23,000 lm (@ 100h)
Luminous Efficacy: 92 lm/W (@ 100h)
Colour Temperature & CRI: CCT: 2150K CRI: Ra 65
Chromaticity Co-ordinates: CCx: CCy:
Rated Lifetime: 10,000 hours to 90% flux & survival
Warm-up & Re-strike time: 6 min. to 80% flux Restrike <2 minutes
Burning Position: Universal
Overall Length: 257 mm 10 1/8 inches
Light Centre Length: 158 mm 6 1/4 inches
Factory: Turnhout Belgium
Date of Manufacture: August 1989
Original / Present Value: GP £44.57 (1988) £104.30 (2013)
 
References: 1) The High Pressure Sodium Lamp, Sjef de Groot & Johan Van Vliet, Philips Technical Library, 1986, ISBN 90 201 1902 8.
2) Philips Training Manual MTO Turnhoutlampen, Hogedruk-Natriumlampen, C.A.J Jacobs & M. van Delm, 1987, pp.26,44.
3) Philips UK Brochure, SON Comfort Lamps, April 1990.
4) Philips UK Lamp Catalogue, 1989/90.
5) Philips UK Price List, August 1988.