Tesla SHC 400W Original HPS Design

Tesla, the state-run lamp manufacturer of the former Czechoslovakia demonstrated its technological lead at the end of the 1960s, by becoming the fourth lampmaker to master HPS technology (after GE of America, Osram-GEC of England, and Thorn Lighting of England). This example is representative of the company's earliest production style and is believed to date to 1967. The development was made by Messrs. Ing. Otto Sofka, and Dr. Milan Neužil.

The arc tube is made of translucent polycrystalline alumina, with very rough surface condition. It is suspected that the light transmission is far below that of modern materials. The tube is not completely circular - at the ends it has been ground, so as to enable it to fit within the niobium sealing cups. The design of these cups is very similar to American GE lamps of the era, and it is possible that they may even have been purchased from GE. The method of sealing the cups to the alumina is believed to be with a frit glass. One of the niobium cups is blind, whereas the other is open and has been brazed to a length of niobium tubing, which forms the exhaust tube. After dosing of the sodium amalgam, the Nb-tube has been sealed off by cold-welding / crimping at three locations. Possibly Tesla had concerns about leakage, hence the decision to apply multiple welds.

The hand-numbered arc tube is enclosed within a standard tubular clear outer jacket of borosilicate glass. Two Barium-aluminium-nickel getters are provided to maintain high vacuum. Unusually these are mounted parallel to the stem, with the result that the Ba-mirror extends far up the outer bulb. Later the angle of the getters was adjusted to keep the mirror closer to the cap.
Manufacturer: Tesla Holešovice
Lamp Power: 400 Watts
Lamp Current: 4.45 Amps
Lamp Voltage: 105 Volts
Cap Type: E40s/45 Ni plated brass + porcelain
Bulb Type: T-46 T-14.5 in eighths/inch
Bulb Finish: Clear Borosilicate
Electrodes: Backwound Tungsten BCT emitter
Arc Length:
Atmosphere: Inner: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 43,000 lm (@ 100 hrs)
Luminous Efficacy: 110 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 2100K CRI: Ra 23
Chromaticity Co-ordinates: CCx: 0.526 CCy: 0.418
Rated Lifetime: ~10,000 hours
Warm-up & Re-strike Time: 5 minutes 1 minute
Burning Position: Universal
Overall Length:
Light Centre Length:
Factory: Praha Factory No.1 Czechoslovakia
Date of Manufacture: 1967 Date Code: 7
Original / Present Value: Unknown
References: 1) Private Communication, Stanislav Slabyhoudek, 25-IX-2002.
2) Private Communication, Stanislav Slabyhoudek, 05-VI-2003.