GE Lucalox Low Power Prototype LU125/BD?

Right from the outset of the high pressure sodium lamp, GE's engineers envisaged a range of lamps having different powers. Following the 1965 launch of the first 400W lamp, a technical paper was published quoting design details for a family of lamps rated 125W, 200W, 275W, 400W, 700W and 1000W. This particular lamp is believed to be a prototype of the 125W rating, which was never launched for sale.

The first lamp in the range was of course the 400W rating, having an arc voltage of about 100V and operating at 4.5A. It was followed in 1966 by a 275W 100V lamp having a narrow bore arc tube, which was re-rated to 250W in 1969 following problems of overheating and short life. The principle of the 700W and 1000W lamps was to maintain the same current, arc tube diameter and electrodes as the 275/400W lamps, but to increase the arc length by about 2.5 times, thereby increasing volt drop and hence the power. Only the 1000W was ever launched. The principle of the smaller lamps seems to have been to maintain the same current and electrodes as the original models, but to halve the arc length, thereby reducing the volt drop and power. Neither of those were launched commercially.

It is interesting to note the unusual end seals of this small lamp. HPS lamps become progressively more difficult to produce at lower powers, due to a relative increase in thermal losses to the cold ends. This lamp is intended for base down operation and has its external amalgam reservoir at the cap side. To ensure that the opposite end does not run sufficiently cool that the amalgam condenses there as well, the usual blind end seal has been shortened, presumably to reduce its thermal mass and heat losses.
Manufacturer: General Electric Company U.S.A.
Lamp Power: 125 Watts ?
Lamp Current: 3.0 Amps ?
Lamp Voltage: 50 Volts ?
Cap Type: E39s/41 Brass + vitrite
Bulb Type: ED-57 ED-18 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: Approx. 10,000 lm
Luminous Efficacy: Approx. 80 lm/W
Colour Temperature & CRI: CCT: 2100K CRI: Ra 22
Chromaticity Co-ordinates: CCx: 0.522 CCy: 0.423
Rated Lifetime: Not published
Warm-up & Re-strike Time: 3-4 minutes 1 minute
Burning Position: Vertical Base Down ± 95°
Overall Length: 248 mm 93/4 inches
Light Centre Length: 146 mm 53/4 inches
Factory: Cuyahoga, NELA Park Cleveland OH, U.S.A.
Date of Manufacture: Approx 1970
Original Value: Unknown
References: 1) High-Intensity Sodium Lamp Design Data for Various Sizes, W.C.Louden & W.C.Matz, Illuminating Engineering, September 1966, pp. 560-561