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Thorn SONDL-T Deluxe Colour 400W |
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) | |
