GE Lucalox LU250 Universal with Butterfly Crimp
GE's first HPS lamp of 1965 was a Universal design - a feature that was lost with the 1967 introduction of the external amalgam reservoir. That improved lamp life and performance, but the asymmetric arc tube meant that lamps had to be produced in base up and base down variants. The risk was that if the reservoir was situated uppermost, slight vibration would cause liquid amalgam to fall into the arc tube. The resulting sudden rise in vapour pressure and arc voltage could cause the lamp to extinguish, or the droplet might even crack the hot ceramic due to thermal shock.

This problem was overcome with the 1977 invention of Charles McVey, which became known as the Butterfly Crimp design and once again allowed the Lucalox lamp to function reliably in all burning positions. It consists of flattening a portion of the niobium sealing tube around the tungsten shank of the electrode, while leaving two narrow channels open. These allow passage of sodium vapour between the reservoir and arc tube, but prevent flow of liquid amalgam. The butterfly crimped Nb tube is sealed into the ceramic arc tube with an intermediate ceramic plug, and GE's G-54 frit sealing glass (54% Al2O3, 38.5% CaO, 7.5% MgO).

Another advantage of this construction is that it eliminated the need for TIG-welding of the tungsten electrode to the niobium tube, which caused embrittlement of the tungsten, especially with small low power electrodes. Still another advantage was the reduction the the amount of niobium used vs the old end cap design. The opposite end of the arc tube uses an alumina plug with niobium wire seal, combined with frit-distributing lateral tie-wire, which was introduced in 1975 to replace the costly niobium cup at that end.
Manufacturer: General Electric Company U.S.A.
Lamp Power: 250 Watts
Lamp Current: 3.0 Amps
Lamp Voltage: 100 Volts
Cap Type: E39s/41 Brass + vitrite
Bulb Type: ED-57 ED-18 in eighths/inch
Bulb Finish: Clear Lead borosilicate glass
Electrodes: Backwound Tungsten Ba2CaWO6 Emitter
Arc Length:
Atmosphere: Inner: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 27,500 lm (@ 100 hrs) 24,750 lm (average)
Luminous Efficacy: 110.0 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 1900K CRI: Ra 22
Chromaticity Co-ordinates: CCx: 0.512 CCy: 0.422
Rated Lifetime: 24,000 hours to 50% survival
Warm-up & Re-strike Time: 3-4 minutes 0.5-1.5 minutes
Burning Position: Universal
Overall Length: 248 mm 93/4 inches
Light Centre Length: 146 mm 53/4 inches
Factory: Ravenna, OH U.S.A.
Date of Manufacture: June 1983 Date Code: 42 ∙-
Original Value:
 
References: 1) General Electric USA Large Lamp Catalogue, Form 9200, 1984
2) General Electric USA Large Lamp Catalogue, Form 9200, 1982
3) US Patent 4,065,691, Ceramic Lamp having Electrodes Supported by Crimped Tubular Inlead, C.I.McVey (General Electric), filed Dec. 1976
4) US Patent 3,992,642, Ceramic Envelope Plug and Lead Wire and Seal, C.I.McVey (General Electric), filed Dec. 1975
5) US Patent 4,034,252, Ceramic Lamp Seal and Control of Sealing Frit Distribution, C.I.McVey (General Electric), filed Dec. 1975