Westinghouse Ceramalux-4 Deluxe Sodium
While the high efficacy and long life of the HPS lamp makes it eminently suitable for exterior and industrial lighting, its poor colour rendering excludes it from areas requiring better colour fidelity. This situation was not improved until 1978 when Westinghouse achieved this first practical 'Deluxe' lamp with higher colour rendering - known as Ceramalux-4.

It employs the principle that the spectrum can be improved by operation at higher sodium vapour pressure than regular lamps. An increase from about 10kPa to 45kPa widens the D-line self-reversal width Δλ from 100Å to 280Å, broadening the entire spectrum. This boosts CRI from 20 to 65 and CCT from 1900K to 2400K, with a loss of about 10% efficacy. Higher vapour pressure is achieved by increasing the sodium content of the amalgam from 21 to 25%, and applying heat reflector strips around the arc tube ends. Arc length is reduced and tube diameter increased from 7.2 to 8.0mm, leading to further self-absorption of resonance radiation and still better CRI. The increased sodium pressure attacks the end seals and reduces life - initially to 7,500h. Later this was improved to 10,000h and the CCT reduced to approx 2200K.

The original lamp employed niobium cup end seals, whereas this later model features Westinghouse's low cost niobium wire seals. The arc tube ends are closed by a ceramic washer, held in place during sealing with a specially shaped metal clip. This design later proved to be rather unreliable, due to the substantial quantity of glass sealing frit that flows into the arc tube, reacting with sodium causing more rapid voltage rise and short life. Shortly after Westinghouse's 1982 takeover by Philips, its HPS lamps were re-designed with more reliable monolithic seals to niobium tubes.
Manufacturer: Westinghouse C250S50/DX4
Lamp Power: 250 Watts
Lamp Current: 3.0 Amps
Lamp Voltage: 100 Volts 4000 Volts ignition
Cap Type: E39 Brass + vitrite
Bulb Type: ED-57 ED-18 in eighths/inch
Bulb Finish: Clear Lead borosilicate glass
Electrodes: Backwound tungsten Ba2CaWO6 emitter
Arc Length 50 mm 2 inches
Atmosphere: Inner: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 25,000 lumens @ 100h 22,500 @ 10,000h
Luminous Efficacy: 100.0 lm/W @ 100h
Colour Temperature & CRI: CCT: 2200K CRI: Ra 65
Chromaticity Co-ordinates: CCx: 0.505 CCy: 0.410
Rated Lifetime: 10,000 hours to 50% survival
Warm-up & Re-strike Time: 7-10 minutes 1 minute
Burning Position: Universal
Overall Length: 248 mm 9¾ inches
Light Centre Length: 146 mm 5¾ inches
Factory: Bath, NY U.S.A.
Date of Manufacture: 1982 July Date Code: 7 2
Original Value: US $71.00 (1980)
References: 1) Westinghouse Large Lamp Catalogue, January 1980, USA.
2) HPS Lamps with Improved Colour Rendering, R.S. Bhalla, D.A. Larson, M.C. Unglert, Journal of the IES V.5 No.4 1979 June p.202-206
3) Some Important Factors in Design of a Color Improved High Pressure Sodium Lamp, R.S. Bhalla, LS:2 Symposium, Enschede (Holland), 1979
4) Ceramalux-4 High Pressure Sodium Lamp, Lighting Design & Application, December 1978, pp.30-31
5) Photometric measurement at rated power after ageing