Philora ML500 MercuryBlended First Generation

The so-called ML "Mixed Light" lamp was Philips' improved version of the original mercury blended MAT lamps that were developed by British Siemens a few years earlier. Whereas the Siemens originals employed hard glass medium pressure discharge tubes, Philips created its ML lamps around the compact and more efficient quartz arc tubes.

This presents a light source of much more compact dimensions, in which it is possible to mount both the filament and discharge tube at the same height, facilitating optical control. Furthermore, to minimise colour separation effects, the bulb is internally etched to give it the 'pearl' finish, which thoroughly homogenises the light. The resulting lamp is equipped with an E40 screw base and offered in the same dimensions as a comparable GLS incandescent lamp. This lamp is the ML500 version (the 500 signifying its luminous flux in dekalumens, the traditional unit of measure for Dutch and German lamps years ago).

The arc tube form is one of the earliest types employed by Philips, in fact the second type that was commercially employed. First the molybdenum foils to which the main electrodes are welded were sleeved in a layer of quartz, which was shrunk down under vacuum, over this area only. Then the assemblies were loaded into the arc tube itself, which was again shrunk down over the inner quartz sleeves. At the base end of the lamp, a third foil for the auxiliary electrode is sandwiched between the arc tube and this inner quartz sleeve. The auxiliary itself is made from a flat sliver of tungsten sheet, presumably to make it thin enough to easily pass through the gap into the seal. The precise construction is visible in the X-Ray shadowgraph to the left.
Manufacturer: Philips Lighting
Lamp Power: 250 Watts
Lamp Current: 1.14 Amps
Lamp Voltage: 225 Volts
Cap: E40s/45
Bulb Finish: Pearl
Bulb Type: PS-110 Soda-lime
Overall Length: 240 mm
Light Centre Length:
Electrodes: Single Coil Thorium strip emitter
Inner / Outer Atmosphere: Inner: Ar | Hg Outer: Nitrogen
Luminous Flux: 5,000 lm (at 100 hours)
Luminous Efficacy: 20.0 lm/W (at 100 hours)
Colour Temperature & CRI: CCT: 3800K CRI: Ra 60
Chromaticity Co-ordinates: CCx: 0.349 CCy: 0.380
Burning Position: Vertical
Rated Life: 2,000 hours (to 50% survival)
Warm Up / Re-strike Time: 4 minutes 10 minutes max.
Factory: Emmasingel, The Netherlands
Date of Manufacture: circa 1940-45
Original Value:
References: 1) Philips Brochure ML500 Lamps, 1939 Belgium