Sylvania SHP-TS Mercury-Free
The first reported high pressure sodium lamps were in fact mercury-free types. However mercury was added to the first commercialised lamps in the form of an Na/Hg amalgam. It serves to raise efficacy, owing to the reduced thermal conductivity and losses from the Na-Hg-Xe plasma. It also acts as a buffer gas, decreasing electrical conductivity so that shorter arc tubes can be used. Finally it allows the colour point to be brought on to the blackbody locus. Owing to the low plasma temperature it is scarcely excited and contributes no direct radiation of its own.

Recently it has become desirable to eliminate mercury for environmental reasons. Also with normal sodium loss during life, the discharge in the increasingly Hg-rich plasma causes a lamp voltage rise, which leads to cycling and eventual failure.

The development of the high Xenon pressure lamp in the 1980s made it possible to replace the Hg content with a similar pressure of xenon. However since mercury was used to decrease the electrical conductivity of the plasma, its removal means that longer and thinner arc tubes are needed to control the volt drop, such that standard lamps can be retrofitted. This results in a small loss of efficacy compared to "Super" HPS lamps with mercury, but the Hg-free lamps remain more efficient than conventional standard HPS types.

The mercury in standard lamps causes some broadening of the red-wing of the sodium spectrum, and this is absent for the Hg-free lamp (see spectrum below). Consequently the they appear slightly yellower than standard types. The colour temperature is around 100K higher with CRI a little lower, and colour is shifted somewhat away from the blackbody locus.
Manufacturer: Sylvania Lighting International
Lamp Power: 100 Watts
Lamp Current: 1.2 Amps
Lamp Voltage: 100 Volts
Cap Type: E40s/45 Ni plated brass + vitrite
Bulb Finish: Clear Soda-lime glass
Bulb Type: T-46 T-14½ in eighths/inch
Overall Length: 211 mm 8 5/16 inches
Light Centre Length: 127 mm 5 inches
Arc Length:
Electrodes: Backwound Tungsten BaSr3Y8O16 emitter
Atmosphere: Na,Hg | Xe 300 torr Outer: Hard Vacuum
Luminous Flux: 10,000 lm @ 100 hours
Luminous Efficacy: 100.0 lm/W @ 100 hours
Colour Temperature & CRI: CCT: 2100K CRI: Ra 18
Chromaticity Co-ordinates: CCx: 0.527 CCy: 0.434
Burning Position: Universal
Rated Lifetime: 24,000 hours to 50% survival
Warm-up & Re-strike Time: 3 minutes 5 minutes
Factory: Tienen Belgium
Date of Manufacture: March 1996 Date Code 3
Original & Present Value:
 
References: 1) R. Geens & E. Wyner,Progress in High Pressure Sodium Lamp Technology", IEE Proceedings-A Vol. 140 No. 6, November 1993.
2) Sylvania brochure SHP Mercury-Free, March 1995.