Solarcolour Deluxe SONDL-T 400W
While the high efficacy and long life of the HPS lamp makes 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 being employed in such applications as office or even shop window lighting, to achieve higher light levels at low cost. Naturally the results were unsatisfactory, and efforts began on improving the colour rendering properties of this light source.

Osram-GEC was one of the pioneers in this field, launching its first Solarcolour Deluxe lamp in 1981. Initially offered only in 250W rating with internal ignitor, it was soon joined by 150W and 400W models for use with external ignitors. These lamps employ the principle that an increase in sodium vapour pressure results in further broadening of the spectrum, which leads to a higher colour rendering index at the expense of efficacy. The sodium pressure has been increased by a combination of applying heat-reflectors of niobium around the arc tube in the area behind the electrodes, so as to raise the amalgam temperature, and reducing the arc length. To prevent the short life that would otherwise arise from overloading the ceramic discharge tube, its diameter has been increased. Ordinarily such changes would result in a greenish light, and to bring the colour point back to the blackbody locus the mole fraction of sodium in the amalgam is adjusted to about 80%.

The ceramic arc tube has a 3-piece construction, and the end seals are to niobium tubes with additional ceramic end-buttons to increase the seal length. One niobium tube is blind, the other being open so as to exhaust the arc tube.
Manufacturer: The General Electric Company of England PLC
Lamp Power: 400 Watts
Lamp Current: 4.45 Amps 6.6A during starting
Lamp Voltage: 105 ±15 Volts 1000V ignition
Cap Type: E40s/45 Ni plated brass + vitrite
Bulb Type: TD-51 TD-16 in eighths/inch
Bulb Finish: Clear Borosilicate glass
Electrodes: Backwound Tungsten BCT Emitter
Arc Length: 90 mm 31/2 inches
Atmosphere: Inner: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 38,500 lm (@ 100 hrs) 36,000 lm (average)
Luminous Efficacy: 96.3 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 2200K CRI: Ra70
Chromaticity Co-ordinates: CCx: 0.506 CCy: 0.418
Rated Lifetime: 10,000 hours 70% survival, 75% lumens
Warm-up & Re-strike Time: 5 minutes 15 minutes
Burning Position: Universal
Overall Length: 285 mm 111/4 inches
Light Centre Length: 175 mm 67/8 inches
Factory: Shaw, Oldham England
Date of Manufacture: October 1985 Date Code SK
Original / Present Value: GB £57.27 (1988) GB £137.10 (2014)
 
References: 1) Osram-GEC Lamp Catalogue, UK, 1985/86, p.223
2) Osram-GEC Solarcolour Brochure, 1981
3) Osram-GEC Solarcolour Brochure, c.1985
4) Osram-GEC Price List, Apri 1988