GE Lucalox LU1000/BD with Auxiliary Electrode
Following the introduction of GE's original 400W HPS lamp in 1965, the range was quickly expanded. A 275W rating followed in 1966, and was adjusted to 250W in 1969. Next came the 1000W in 1971-72, at first in a cylindrical T-18 bulb, which was replaced in the late 1970s by the more common ET-25 conical envelope. This particular example has an unusual ED-25 bulb which was never listed for sale, and is believed to be an early prototype of the 1000W lamp.

American 1000W HPS lamps are different than those in the rest of the world. Normally it is desirable to set the voltage of a discharge lamp to about half the mains voltage - and since the first developments were in Europe with 200-260V mains, this resulted in lamps of around 100-130V. When discharge lamps were adopted in the Americas where mains voltages are lower, the lamp designs were not changed. Instead autotransformer ballasts were developed, which first boost the mains to European voltages, then regulate the current. This results in large, complex and inefficient ballasts - but does give the lamp engineer more freedom. When GE came to develop the first 1000W lamp it built on this flexibility by departing from its established 400W arc tube design, and while holding lamp current the same, simply increased arc voltage by a factor 2.5 from 100V to 250V. This allows use of the same electrodes and the same diameter of arc tube. The only necessary change is an increase in arc length to attain the higher volt drop.

This lamp has an unusual wire loop around the centre of the arc tube. Its purpose is unknown - possibly it was to aid starting of the unusually long arc - the loop diameter being set to avoid sodium loss due to its electric field.
Manufacturer: General Electric Company U.S.A.
Lamp Power: 1000 Watts
Lamp Current: 4.7 Amps
Lamp Voltage: 250 Volts
Cap Type: E39s/41 Ni Plated Brass + Vitrite
Bulb Type: ED-79 ED-25 in eighths/inch
Bulb Finish: Clear Lead borosilicate glass
Electrodes: Double tungsten coils Ba2CaWO6 Emitter
Arc Length:
Atmosphere: Inner: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 130,000 lm (@ 100 hrs)
Luminous Efficacy: 130.0 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 2100K CRI: Ra 22
Chromaticity Co-ordinates: CCx: 0.522 CCy: 0.423
Rated Lifetime: Unknown
Warm-up & Re-strike Time: 3-4 minutes 1 minute
Burning Position: Base Down ± 95°
Overall Length: 383 mm 151/16 inches
Light Centre Length: 222 mm 83/4 inches
Factory: Cuyahoga, NELA Park Cleveland OH, U.S.A.
Date of Manufacture: Prior to 1971/72
Original Value: Unknown
 
References: 1) General Electric USA Large Lamp Catalogue, Form 9200, 1972