Sylvania SHP-T Standby with Twin Arc Tubes

Sylvania is inventor of the so-called Standby SON lamp pictured here, which incorporates two identical arc tubes electrically connected in parallel. The purpose is two-fold.

The principal reason for the development is that when the electricity supply is restored after a momentary interruption, there is a second cool arc tube inside the lamp which can be illuminated instantaneously without delay. The hot arc tube which was in use beforehand cannot be ignited for several minutes until after it has cooled down, and in certain applications the delay may be unacceptable.

In addition, the fact that the lamp contains two arc tubes means that its service life can effectively be doubled. This is particularly useful in installations where maintenance is difficult.

However the lamp remains to become well accepted by street lighting agencies where maintenance costs are considerable. Partly this is on the grounds of the higher initial lamp price, but also it is found that this lamp does not function quite so efficiently in many of the more compact modern lanterns. To accommodate two arc tubes, they must be offset from the central axis of the lamp and consequently they can no longer reside at the optical centre of the reflector system. There can also be a not inconsiderable change in beam profile from one day to the next, depending on which arc tube happens to strike up first (a random event) .

Nevertheless, particularly in the low wattage sizes and where the lamp is employed for security lighting, the instant re-strike feature is invaluable and here it finds a sizeable market.
Manufacturer: GTE Sylvania
Lamp Power: 392 Watts
Lamp Current: 4.65 Amps
Lamp Voltage: 100 Volts
Cap Type: E40s/45 Ni plated brass + vitrite
Bulb Finish: Clear Hard glass
Bulb Type: T-46 T-14½ in eighths/inch
Overall Length: 280 mm 11 inches
Light Centre Length: 175 mm 6¾ inches
Arc Length:
Electrodes: Backwound Tungsten Barium Calcium Tungstate
Atmosphere: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 48,000 lm (@ 100 hrs) 47,000 lm (@ 14,000hrs)
Luminous Efficacy: 120.0 lm/W (@ 100 hrs) 117.5 lm/W (@ 14,000hrs)
Colour Temperature & CRI: CCT: 2050K CRI: Ra 25
Chromaticity Co-ordinates: CCx: 0.520 CCy: 0.420
Burning Position: Universal
Rated Lifetime: 28,000 hours to 70% survival
Warm-up & Re-strike Time: 5 minutes Instantaneous restrike
Factory: Arc Tubes: Shipley, UK Lamp: Tienen, Belgium
Date of Manufacture: 1988
Original & Present Value: £60.13 (1989) £100.22 (2005)
References: 1) GTE Sylvania UK Lamp Catalogue 1988/89.
2) GTE Sylvania UK Price List 1989.
3) GTE Sylvania Brochure, SON Extra, 1990 UK
4) GTE Sylvania Brochure, Sodium SBY Extra, 1991 Switzerland