Thorn SONDL-T Deluxe Colour 400W

The poor colour rendering of HPS lamps has been improved in the "Deluxe" family, invented by Westinghouse in 1978. GE followed in 1980, Osram-GEC in 1981, and Thorn in 1982. Thorn's range began with 150W & 250W diffuse ovoid lamps, being joined by 400W and tubular models in 1983.

Deluxe HPS lamps feature a broader spectrum, thanks to operation at still higher sodium vapour pressures. An increase from about 10kPa to 45kPa widens the D-line self-reversal Δλ from around 100Å to 250Å, and more light is produced in the red and blue wings of the spectrum. This boosts the CRI from ~25 to 50-70 and CCT from 1900 to 2200K, but at the expense of efficacy since the eye is relatively insensitive to the deep red and blue wavelengths.

Sodium pressure is increased by shortening the gap behind the electrodes and applying niobium heat screens around the ends, to raise amalgam temperature. Owing to the very high loading, these are graded in steps of 0.1mm length and matched to individual arc tubes. CRI is further increased by using wider arc tubes, which amplifies the self-absorption of resonance radiation. The increased diameter requires a shorter arc to maintain optimum thermal balance. Ordinarily such changes would result in a greenish light, and this is counteracted by increasing the sodium ratio in the amalgam. At such high sodium pressures the chemical reactions in the arc tube are accelerated, which leads to more rapid voltage rise and lamp life is approximately halved. This arc tube has a 3-piece monolithic construction, with additional ceramic buttons to increase the seal length. It is of Thorn's most recent design, in which the diameter of the niobium tubes has been reduced to just 1.75mm to increase seal reliability.
Manufacturer: Thorn Electrical & Musical Industries Ltd.
Lamp Power: 400 Watts
Lamp Current: 4.6 Amps
Lamp Voltage: 100 Volts
Cap Type: E40s/45 Ni plated brass + vitrite
Bulb Type: TD-46 TD-14½ in eighths/inch
Bulb Finish: Clear Borosilicate glass
Electrodes: Backwound Tungsten BCT Emitter
Arc Length: 56.0 mm 2.205 inches
Atmosphere: Na25:Hg75 | Xe 20 torr Outer: Hard Vacuum
Luminous Flux: 35,000 lm (@ 100h) 34,000 lm (@ 2000h)
Luminous Efficacy: 87.5 lm/W (@ 100h)
Colour Temperature & CRI: CCT: 2200K CRI: Ra 25
Chromaticity Co-ordinates: CCx: 0.505 CCy: 0.412
Rated Lifetime: 12,000 hours 50% survival, 75% flux
Warm-up & Re-strike Time: 8 minutes <1 minute
Burning Position: Universal
Overall Length: 285 mm 111/4 inches
Light Centre Length: 173 mm 67/8 inches
Factory: Leicester England
Date of Manufacture: March 1988 Date Code: 75
Original Value: GB £57.27 (1998)
References: 1) Thorn Lighting Comprehensive Catalogue, UK, 1983.
2) Thorn Lighting Comprehensive Catalogue, UK, 1984/85.
3) Thorn Lighting Comprehensive Catalogue, UK, 1987/88.
4) Thorn Lighting Brochure, Discharge Lamps, Publication 44748, 1989.
5) Thorn Lighting Brochure, SON-Deluxe Lamps, 1982.
6) Thorn Lighting Product Data Sheet 400W SONDL-T 96-3046C, 23-6-1986.
7) Thorn Lighting SON Manufacturing Specifications.