RLOD#2 (06.05.2020) Mid-1980s Philips MPDL 35W DV27

The 1980s saw the development and release of compact low-wattage metal halide lamps intended for various lighting applications that were traditionally catered for by inefficient incandescent lamps. All the major lamp manufacturers were involved in that effort and Philips was the first company to address the automotive headlight market around the mid-1980s. To that end, the Dutch developed 30–35 W discharge lamps filled with an efficient sodium-scandium salt mix which enables a source efficacy of 90 lm/W, about four times as high as that of standard tungsten-halogen headlight lamps. Early tests and experiments were successful to the point of launching the Micro Power Discharge Lamp/Lighting (MPDL, later MPXL) project in which the technology was successfully developed into a commercial product.

The MPDL 35W DV27 shown here is an early prototype made in the mid-1980s. This lamp is already a rather advanced concept featuring a molded frame made of a phenolic resin and in which lead wires are embedded. Such design provides the necessary structural rigidity and galvanic insulation to the lamp. The miniature quartz burner is mounted on conductors protruding from the lamp frame. Typical of the early days of that technology, the arctube features mechanically pinched end seals and an exhaust tip. Back then, instant light on and hot restrike were not yet of concern, so the MPDL burner was filled with argon to facilitate ignition (while cold) at a relatively low voltage of less than 2 kV. This would change dramatically in the following years though. Another interesting design feature is the side reflector mounted on the lamp frame. This part is made of a solid piece of aluminum, machined and polished into a concave mirror on the burner side so as to reflect light back to its source, and coated with a black iron silicate paint on the other side in order to limit stray light reflections in the luminaire. Such design allows a good thermal management of the semi-confined lamp while increasing the amount of light projected in one specific direction.