||The MHN-T lamp featured here marked the first entry of Philips into the low wattage metal halide market. It is a direct descendent of the earlier experimental Thulium lamp, whose development had to be redirected owing to frequent explosions of the arc tube.
The aggressiveness of thulium iodide towards the quartz arc tube was tamed by using it in conjunction with dysprosium and holmium iodides. These also assisted in correcting the slightly greenish-yellow coloured light of the thulium lamp.
Still the problem of arc tube explosions would sometimes occur, and to enable the development of a new series of compact open-fronted luminaires to accompany this new lamp, it was necessary to make it in a shatterproof format. Two heavy-walled quartz shrouds surround the arc tube, the ends of the shrouds being capped with metal plates.
A slim clear tubular outer jacket is employed, to capitalise on the very short arc gap, and allow excellent optical control when positioned at the focal point of a reflector. With standard E27s screw bases the arc tube position is not well controlled with respect to the lampholder. Consequently the base of this lamp was re-designed as a push-fit pre-focussed design. The base was originally manufactured in white polycarbonate, but owing to the slight discolouration that is sometimes noticed at end of life, it was changed to a nickel plated brass metal shell after a few years. The mechanical arrangement and dimensions of this lamp are the same as for Philips SDW-T White SON, and the two types could therefore be built into the same luminaire to provide a choice of colour.