Lucalox LU100/BD with Flux Polished Arc Tube

Ever since the inception of the first high pressure sodium lamps, based on GE's invention of translucent polycrystalline alumina as an arc tube material, the light-scattering nature of this ceramic has been considered a drawback. Nearly all other discharge lamps enjoy optically transparent glass or quartz materials, but HPS performance has been hindered by the lack of a transparent material that can endure the very corrosive sodium at high temperatures and pressures.

In parallel with GE's 1961 invention of the polycrystalline material, detailed in US Patent 3,026,210, the company filed US 3,026,177 detailing a process to create transparent alumina, but its cost and manufacturing complexity was too high to justify its use in a lamp. The first notable progress in creating an alumina ceramic having higher transparency and acceptable cost was achieved by the so-called Flux Polishing technique, featured in this lamp and detailed in GE's 1974 patent US 3,935,495. The improved transparency of this arc tube is clearly visible in the adjoining photographs.

The process consists of immersing a polycrystalline alumina arc tube in a bath of molten sodium borate. This etches the surface, preferentially attacking grain surfaces instead of the boundaries. After withdrawal any adherent salt and vitreous reaction products are washed off in mineral acid, and the result is a polycrystalline tube having a polished surface and high in-line transmission. Luminous flux of HPS lamps using this arc tube material is about 2% greater than for untreated ceramic. However the process is costly and it was soon phased out, in favour of a better polycrystalline material with improved in-line transmission which delivered a similar efficacy increase from a diffuse arc tube material.
Manufacturer: General Electric Company U.S.A.
Lamp Power: 100 Watts
Lamp Current: 2.1 Amps
Lamp Voltage: 55 Volts
Cap Type: E39s/41 Brass + blue glass
Bulb Type: ED-75 ED-23½ 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: 9,500 lm (@ 100 hrs) 8,550 lm (@ 6000 hrs)
Luminous Efficacy: 95.0 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 2100K CRI: Ra 22
Chromaticity Co-ordinates: CCx: 0.522 CCy: 0.423
Rated Lifetime: 12,000 hours to 50% survival
Warm-up & Re-strike Time: 3-4 minutes 1 minute
Burning Position: Universal
Overall Length: 197 mm 7 3/4 inches
Light Centre Length: 127 mm 5 inches
Factory: NELA Park, Cleveland OH U.S.A.
Date of Manufacture: November 1976 Date Code: 59 -
Original Value: Unknown
References: 1) General Electric USA Large Lamp Catalogue, Form 9200, 1977
2) General Electric USA Large Lamp Catalogue, Form 9200, 1975
3) US Patent 3,935,495 - Chemically Polished Polycrystalline Alumina - Scott & Levenson, General Electric, app. March 1974