GE Lucalox LU50/90/D/27 with Diffuse Coating
Although the Americans were first to introduce HPS lamps, for the first decade they were offered only in clear bulbs. The original models were introduced with a new ED-18 bulb, having a slender ellipsoidal form designed to achieve an isothermal profile. Its size was set to match the temperature of mercury envelopes, and could be smaller because sodium lamps are under vacuum vs gasfilled for mercury, thereby reducing heat losses. American HPS lamps were at first used almost exclusively in new luminaires specifically designed for them, or to replace old clear mercury lamps which remained popular far longer in the USA than the rest of the world.

Meanwhile in Europe, even before the launch of HPS, clear mercury lamps had been almost entirely superseded by the superior phosphor-coated types in large ovoid bulbs. There was more interest in applying HPS to upgrade existing luminaires, and as such they were offered from the outset in both clear and diffuse bulbs. The bulb coating was, of course, changed from the fluorescent powders used with mercury lamps to a simple light-scattering material since the sodium lamp has no appreciable UV output. This enabled HPS lamps to achieve similar light distribution to mercury lamps without need to redesign luminaire optics. Glare is also considerably lower with diffuse lamps, and there is less voltage rise due to light reflected back onto the arc tube.

It was not until 1975 that diffuse HPS lamps were launched in the USA, GE being first with a 150W model in ED-28 bulb. This lamp is representative of the company's first 50W and 70W versions which employed a non-standard E-21 bulb until the early 1990s. The coating is unusually of aluminium oxide powder, which suffers a high light loss of about 7%.
Manufacturer: General Electric Company U.S.A.
Lamp Power: 50 Watts
Lamp Current: 0.76 Amps
Lamp Voltage: 90 Volts
Cap Type: E27s/27 Brass + vitrite
Bulb Type: E-67 E-21 in eighths/inch
Bulb Finish: Diffuse Al2O3 powder Lead borosilicate glass
Electrodes: Backwound Tungsten Ba2CaWO6 Emitter
Arc Length:
Atmosphere: Inner: Na,Hg | Xe Outer: Hard Vacuum
Luminous Flux: 3,300 lm (@ 100 hrs) 2,970 lm (average)
Luminous Efficacy: 66.0 lm/W (@ 100 hrs)
Colour Temperature & CRI: CCT: 1900K CRI: Ra 22
Chromaticity Co-ordinates: CCx: CCy:
Rated Lifetime: 16,000 hours to 50% survival
Warm-up & Re-strike Time: 5 minutes approx 2 minutes
Burning Position: Universal
Overall Length: 160 mm 61/4 inches
Light Centre Length: 105 mm 41/8 inches
Factory: Ravenna, OH U.S.A.
Date of Manufacture: July 1987 Date Code: 91 ∙-
Original Value: Unknown
 
References: 1) General Electric International Large Lamp Catalogue, Form ILD9200, 1986
2) HPS Lamp Design - a Diversification in Design Wattage & Optical Control, B.R.Collins & S.A.Mule, Lighting Design & Application, Mar.1977, pp.26-31