Westinghouse C70S62/PAR Coal Mine Dichroic HPS
In 1978 Westinghouse launched one of the earliest HPS reflector lamps, specially adapted to meet the requirements of American coal mines. Since the 1940s the American manufacturers offered a similarly unique incandescent lamp for this application. It made use of a rough service filament to withstand the shocks and vibrations of the application, and an unusual side prong base which reduced the dept of protrusion of the lamp face into narrow tunnels. These incandescent PAR lamps brought a considerable increase in useful illuminance vs the earlier non-directional incandescent lamps. However the heat radiation in the beam was considerable, which made working in the already hot underground environment even more uncomfortable for the miners.

This unusual Westinghouse development maintains the side-prong PAR38 format, and is perhaps the first embodiment of an HPS lamp in a sealed beam reflector and also the first combination of an electric discharge lamp with a dichroic reflector. The reflector coating appears similar to that used for general lighting incandescent lamps and its function is to allow heat to escape from the back of the lamp, while projecting only the visible light forwards. The front lens has a texture to produce a very wide beam angle. The increase in useful light output of this lamp plus the reduction in heat load made it relatively successful in this niche application.

The arc tube construction is typical of Westinghouse's earliest lamps, and employs a pair of niobium cup seals at each end of the arc tube, with an external amalgam reservoir. The usual barium getter in the outer envelope, which would interfere with the dichroic coating, has been replaced by a strip of solid-state zirconium-aluminium getter.
Manufacturer: Westinghouse
Lamp Power: 70 Watts
Lamp Current: 1.6 Amps
Lamp Voltage: 52 Volts
Cap Type: Medium Side Prong Brass + Porcelain
Bulb Type: PAR-122 PAR-38 in eighths/inch
Bulb Finish: Dichroic Borosilicate glass
Electrodes: Double tungsten coils Ba2CaWO6 Emitter
Atmosphere: Inner: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 4,500 lumens @ 100h
Luminous Efficacy: 68.3 lm/W
Beam Distribution: 60° to half-peak
Colour Temperature & CRI: CCT: 2100K CRI: Ra 22
Chromaticity Co-ordinates: CCx: 0.522 CCy: 0.423
Rated Lifetime: 7,500 hours
Warm-up & Re-strike Time: 3-4 minutes 1 minute
Burning Position: Universal
Overall Length: 110 mm 4.3125 inches
Light Centre Length: N/A
Factory: Fairmont VA U.S.A.
Date of Manufacture: Approx. 1978-1983 Date Code: .W E S T I N G
Original Value: US $75.00 (1978)
 
References: 1) Westinghouse Large Lamp Catalogue, February 1978, USA.
2) Revolution in Lamps : A Chronicle of 50 Years of Progress, R.Kane, publ. The Fairmont Press Inc. (2001), p.275.
3) A New High Pressure Sodium Reflector Lamp for Mine Service, Lighting Design & Application June 1978 p.60.
4) Annual Progress Report - New Lamps, Lighting Design & Application December 1978 p.25.