Philips Mercury Blended ML 160W Clear
Philips was one of the early pioneers in self-ballasted mercury blended lamps, and within about five years of the introduction of the first medium-pressure MAT lamp by Siemens of UK, Philips had introduced a superior high pressure version in the form of its ML500 'Mixed Light' lamp. The original ML lamps were produced with pearl-frosted bulbs to blend the light from the mercury arc and tungsten filament. For a brief period during the 1940s-50s they were also made available in clear bulbs such as this example, but soon reverted to frosted glass and from around 1965 were superseded by MLL lamps with lumninescent outer bulbs.

This example is representative of the Philips construction of the 1950s. The quartz arc tube is of modern style having pinch-seals, and the electrodes are unusual in that they have no protruding tip, this allowing greater stability in case of mains voltage fluctuations. A single auxiliary ignition electrode is present, connected via a thermally stable resistor made from an extruded rod of magnesium titanate.

Of particular interest is the addition of a novel getter in the outer bulb, consisting of a coiled-coil of reactive metal such as zirconium or tantalum placed over one of the wires to the filament. Its purpose is to absorb hydrogen impurities in the outer bulb, a gas which is particulary toxic to low power mercury blended lamps. Hydrogen molecules are small enough to be able to diffuse into the quartz arc tube, where they cause an increase in the starting voltage as well as the reignition voltage of the arc on each half-cycle of the mains. Too high a voltage makes ML lamps susceptible to extinguish during mains voltage dips, especially if burned non-vertically, and the new getter greatly improved lamp reliability.
Manufacturer: Philips Model 57270E/00
Lamp Power: 160 Watts
Lamp Current: 0.75 Amps
Lamp Voltage: 230 Volts
Cap Type: E27s/30 Ni plated brass + vitrite
Bulb Type: PS-90 PS-28 in eighths/inch
Bulb Finish: Clear Soda-lime glass
Electrodes: Coiled-Coil tungsten Ba-Ca-Y-tungstate emitter
Arc Length: 16 mm 0.630 inches
Atmosphere: Inner: Hg | Ar (18 atm) Outer: Ar:N2 (600 torr)
Luminous Flux: 2,750 lm @ 100 hrs
Luminous Efficacy: 17.2 lm/W @ 100 hrs
Colour Temperature & CRI: CCT: 3800 K CRI: 60 Ra
Chromaticity Co-ordinates: CCx: 0.349 CCy: 0.380
Lifetime: 3,000 hours 50% survival
Warm-up & Re-strike Time: 4 minutes 10 minutes max
Burning Position: Universal Vertical ± 30°
Overall Length: 184 mm 7¼ inches
Light Centre Length: 130 mm 5⅛ inches
Factory: Emmasingel, Eindhoven The Netherlands
Date of Manufacture: 1955 approx.
Original Value: DM 19/- (1956)
 
References: 1) Philips Lamp Catalogue, 1955 International Edition, p.B11
2) Philips Training Manual MTO Turnhoutlampen, Hogedruk-Kwiklampen, Van der Stap & Goethals, 1986, pp.6,39,81
3) Getters for Lamps, E. Rabusin, publ. SAES Getters S.p.A., Italy 1982, pp.11-13
4) The High Pressure Mercury Vapour Lamp, W. Elenbaas, publ. Philips Technical Library, Netherlands 1965, pp.133, 138-140
5) Philips Handbook Kwiklampen en Natriumlampen, Netherlands 1958, p.22
6) Philips Brochure Quecksilberdampflampen, Germany 1956