Osram Metal Halide Powerstar HQI-T 400W/D

During 1989 Osram lauched this 5th generation 400W HQI lamp, which achieved the same feature as its smaller 250W counterpart in that it became suitable for universal burning in all positions. It superseded the earlier /DH and /DV versions for horizontal and vertical burning respectively.

The change was made possible by reducing the length of the arc from 48mm to 33mm. So as to keep the quartz wall loading the same and avoid life compromises, the diameter has been increased. Shorter arcs tend not to bow upwards so significantly when operated horizontally, and this arc tube of low aspect ratio delivers more consistent performance in different burning positions. This allowed the twisted frame of earlier lamps to be replaced by a simple straight wire.

A less-noticeable change is in the electrical properties of the arc. Metal halide lamps have traditionally been designed to run on mercury ballasts, one exception being Osram's smaller HQI-T 250W which was designed from the outset for use on the higher current of an HP sodium ballast. The 1989 redesign of this 400W lamp made the same change, and as such lamp power and luminous flux are notably boosted. The reason for the change is because when reducing arc length, lamp voltage falls. To bring this up to the level for dissipating 400W on a mercury ballast could be done by adding more mercury - but increased mercury pressure exacerbates the convection currents that lead to arc bowing with horizontal burning. To maintain the universal burning design Osram opted for the low mercury dose and offset the low arc voltage by running on the increased current of sodium ballast. Rather inconveniently, this required a ballast change when upgrading to the new lamps.
Manufacturer: Osram GmbH
Lamp Power: 400 Watts
Lamp Current: 4.0 Amps
Lamp Voltage: 110 Volts
Cap Type: E40s/45 Ni plated brass + porcelain
Bulb Type: T-46 T-14½ in eighths/inch
Bulb Finish: Clear Borosilicate
Electrodes: Backwound Tungsten No emitter
Arc Length: 33 mm 1 7/8 inch
Atmosphere: DyI3,TlI,CsI | Ar:Kr85 Outer: Hard Vacuum
Luminous Flux: 33,000 lm @ 100 hours
Luminous Efficacy: 82.5 lm/W @ 100 hours
Colour Temperature & CRI: CCT: 5900K CRI: Ra 85
Chromaticity Co-ordinates: CCx: 0.330 CCy: 0.365
Rated Lifetime: 6,000 hours to 70% flux
Warm-up & Re-strike Time: 2 mins to 80% flux 10-15 minutes
Burning Position: Universal
Overall Length: 285 mm 111/4 inches
Light Centre Length: 175 mm 67/8 inches
Factory: Spandau, Berlin Germany
Date of Manufacture: May 1991 Date Code: qz4
Original / Present Value: GB £64.21 (1991) GB £124.30 (2015)
References: 1) Osram Lichtprogramm Outdoor and Indoor Lighting Catalogue, Germany, 1989/90.
2) Osram Buyer's Guide & Price List, UK, October 1990.