Wotan Daylight Metal Halide HQI-T 400W / DV
This lamp is representative of one of the earliest designs of daylight metal halide developed by German Osram. Of primary interest is the long arc tube, which made the lamp quite sensitive to variations in orientation. This /DV lamp is for use vertically ± 45°, but to satisfy the demand for horizontal operation it was joined later by the /DH version. That has a slightly modified dosing to counteract the effects of the arc bowing upwards, and operates at about 10% reduced efficacy.

The long arc and low wall loading implies a rather low cold spot temperature, especially for the DH type, and as a result the efficacy is not especially impressive. Attempts to overcome this have been made by using a vacuum outer bulb.

The daylight spectrum is produced from a dose based on the iodides of dysprosium, which produces a very high density of spectral lines in the visible region, and thallium which serves to balance the colour point and increase efficacy by virtue of its strong green line. However this chemistry is well known to cause severe arc constriction, which generates strong convection currents and brings the risk of arc instability and flicker. The problem is minimised by the addition of a small amount of caesium iodide, an arc-fattening agent which increases the arc diameter to more stable proportions.

In mid 1989 Osram replaced the /DV and /DH with a new universal burning HQI-T 400W/D. The problems of arc bow were solved by reducing its length from 49 to 29mm, and at the same time designing the lamp for use on a sodium ballast thus increasing its rating from 360W to 420W. However overheating problems saw the lamp modified again in 1999 to the current HQI-BT 400W/D design with bulged outer jacket.
Manufacturer: Osram GmbH
Lamp Power: 360 Watts
Lamp Current: 3.5 Amps
Lamp Voltage: 105 Volts
Cap Type: E40s/45 Ni Plated Brass + Porcelain
Bulb Finish: Clear Borosilicate
Bulb Type: T-46 mm T-14.5 eighths/inch
Overall Length: 285mm 11 1/4 inches
Light Centre Length: 175mm 6 7/8 inches
Arc Length: 49mm 1 15/16 inch
Electrodes: Backwound tungsten
Atmosphere: Hg,(Dy,Tl,Cs)Ix | Ar Outer: Hard Vacuum
Luminous Flux: 28,000 lm @ 100 hrs 700cd/cm2
Luminous Efficacy: 78.0 lm/W @ 100 hours
Colour Temperature & CRI: CCT: 5900K CRI: Ra 85
Chromaticity Co-ordinates: CCx: CCy:
Burning Position: Vertical ± 45°
Rated Lifetime: 6000 hours to 50% survival
Warm-up & Re-strike Time: 4 minutes 10 minutes
Factory: Spandau/Berlin-B Germany
Date of Manufacture: March 1988 Date Code qa3
Original & Present Value: £55.21 (1988) £102.31 (2005)
 
References: 1) Osram Lichtprogramm 1989/90 pp.6.02
2) Osram UK Buyers Guide April 1988 pp.70
3) Osram Powerstar HQI Brochure August 1990
4) "Technology of Special Discharge Lamps", Osram Training Book pp.192.
5) "Taschenbuch der Lampentechnik", Published by Osram GmbH 1987.