Lucalox LU400/BD with External Amalgam Reservoir

In October 1965 GE launched the first HPS lamp. It was rated 400W, and the alumina arc tube was sealed via a glass frit to elongated niobium cups. The sodium amalgam resided within the arc tube. It had a rather short life due to rapid voltage rise from end blackening that raised amalgam temperature, and reactions between sodium and the seals.

The design was improved in 1967 by this lamp, featuring an external amalgam reservoir. The niobium caps are shallower and one of them is pierced by a long niobium tube, which represents a well-controlled cold spot and excess amalgam condenses here. The outer end is pinched closed by cold welding to seal the arc tube. It also extends into the arc tube and is TIG-welded to the electrode shank. At the other end a shorter niobium tube is welded to the cup but does not penetrate inside. It contains an yttrium pellet which acts as a getter for hydrogen diffusing through the niobium cup. Note also the anti back-arcing shields behdind the electrodes to prevent puncture of the niobium cups during starting.

The external reservoir was a success in slowing voltage rise and extending life. It also allowed fine-tuning of voltage, by sandblasting part of its surface to radiate more heat, or applying a niobium band around the arc tube to reduce heat loss. But a drawback was the asymmetric design. The amalgam must always be at the lower end, otherwise it may drip into the arc tube and extinguish the discharge due to a sudden rise in voltage - or crack the ceramic by thermal shock. Separate lamps had to be made for Base Up and Base Down use. It was not until 1977 the GE developed the so-called Butterfly Crimp to keep the amalgam inside the reservoir, that universal lamps became feasible again.
Manufacturer: General Electric Company U.S.A.
Lamp Power: 400 Watts
Lamp Current: 4.7 Amps 7A during starting
Lamp Voltage: 100 Volts 2500-4000V ignition
Cap Type: E39s/41 Ni plated 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: 86.9 mm 3.42 inches
Atmosphere: Inner: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 47,000 lm (@ 100 hrs) 42,300 lm (@ 7,500hrs)
Luminous Efficacy: 117.5 lm/W (@ 100 hrs) 105.8 lm/W (@ 7,500hrs)
Colour Temperature & CRI: CCT: 2100K CRI: Ra 25
Chromaticity Co-ordinates: CCx: 0.512 CCy: 0.420
Rated Lifetime: 15,000 hours to 50% survival
Warm-up & Re-strike Time: 3-4 minutes 1 minute
Burning Position: Vertical Base Down ± 90°
Overall Length: 248 mm 9 3/4 inches
Light Centre Length: 146 mm 5 3/4 inches
Factory: NELA Park, Cleveland OH U.S.A.
Date of Manufacture: August 1971 Date Code: 92 -
Original / Present Value: US $55.00 (1972) £210 (2015)
References: 1) General Electric Large Lamp Catalogue, Form 9200, 1972.
2) General Electric Lamp Specification Bulletin, LU400, 24th September 1971.