Philips HPI-BUS 400W Self-Starting Metal Halide

Philips metal halide lamps of the HPI variety are intended for operation on mercury type ballasts, with the addition of a high voltage ignitor to strike the discharge. Thanks to the arc tube being unusually filled with a neon-argon Penning mixture, the Philips arc tubes only require a 700V soft ignitor. In certain cases it is desirable to further reduce the ignition voltage such that the lamps will strike at ordinary mains voltages, and can thus directly replace a mercury lamp with no need for any ignitor. That is the purpose of the HPI-BUS range (BU = Base Up, S = internal Starter).

The starting voltage is reduced by the addition of a third auxiliary electrode and 20k ohm series resistor, similar to the arrangement in a mercury lamp. This was in fact trialled in the earliest metal halide lamps but was found to reduce lamp life, owing to undesirable electrolytic reactions in the quartz seal between the two electrodes which led to rapid devritrification of the quartz and subsequent arc tube explosions. In the HPI-BUS lamps this problem is alleviated by the use of a thermal switch which short-circuits the two adjacent electrodes once the lamp has warmed up.

The arc tube is dosed with the usual tri-band sodium-indium-thallium halides, with additional red radiation being contributed by lithium impurities from the quartz. A heat-reflective zirconia coating is applied only on one side of the arc tube, which is optimised for cap-up orientation. The outer bulb is filled with a Neon-Nitrogen mixture, so as to prevent loss of the neon from the arc tube since neon can diffuse through quartz at its operating temperature, but not through the glass outer bulb. Originally a 250W HPI-BUS was also produced, but it was not a commercial success.
Manufacturer: Philips Lighting
Lamp Power: 400 Watts
Lamp Voltage: 125 Volts
Lamp Current: 3.4 Amperes
Cap Type: E40/45 Nickel Plated Brass
Bulb Type: ED-120 ED-37 in eighths/inch
Bulb Finish: YVO4:Eu,Tb,Gd Borosilicate
Electrodes: Single Coil ThO2 emitter
Arc Length: 38 mm 1 1/2 inches
Atmosphere: NeAr½% | Hg(Na,In,Tl)Ix Outer: Ne:N2 60:40
Luminous Flux: 31,500 lm @ 100h 28,300 lm @ 2000h
Luminous Efficacy: 78.8 lm/W @ 100h 70.8 lm/W @ 2000h
Colour Temperature & CRI: CCT: 4000K CRI: Ra 65
Chromaticity Co-ordinates: CCx: CCy:
Rated Lifetime: 24,000 hrs to 50% survival
Warm-up & Re-strike Time: 4 minutes 15 minutes
Burning Position: VBU ± 15°  
Overall Length: 282±8 mm 11 1/8 inches
Light Centre Length: 175±5 mm 7 inches
Factory: Turnhout Belgium
Date of Manufacture: October 1987 K7
Original / Present Value: £57.97 (1988) £112.00 (2009)
References: 1) Philips Lighting UK Catalogue 1988.
2) Philips Lighting Brochure "Metal Halide Gas Discharge Lamps", Dec. 1981
3) Philips Lighting UK Price List, August 1988.
4) Philips Training Manual MTO Turnhoutlampen - Metaalhalogenidelampen, F. Oostvogels, D. v.Pijkeren & G. Rouweler, 1985.