1989 Philips MSI 200W/F

Until 1976, Osram’s Metallogen HMI family of daylight metal halide short-arc lamps for stage, studio and projection lighting applications consisted of four models only, all double-ended light sources rated from 575 to 4000 W. That year the Germans released a fifth model, a tiny HMI 200W intended primarily for TV news gathering where portable battery-operated lighting equipments are employed. This breakthrough was made possible by two key innovations: the development of transistor ballasts for high-pressure discharge lamps and the optimization of compact low-wattage high-pressure arc lamps. Replacing incandescent light sources by far more efficient arc lamps allowed a much greater battery life as well as higher illumination levels. Moreover, the production of artificial daylight without filters results in an even greater energy saving compared to incandescent lighting.

The design of the HMI 200W differs significantly from that Osram used for its other HMI lamps. Instead of a central bulged burner attached to vacuum-shrunk end seals, the lamp was made from a single quartz tube, pinch-sealed at its extremities and provided with X515 knife plugs. This design was not new however, it came from the company’s 400 W Halos HCI that was introduced in 1975 for image projection applications. The HMI burner is filled with a mixture of dysprosium and holmium halides, balanced for the production of light at 5600 K with a color rendering index above 90 Ra8. With an electrode gap length of 10 mm, the lamp has the lowest arc power load (169 W/cm) of all metal halide short-arc sources. As a result, the burner is provided with heat-conserving end-coatings to ensure an operation at the lamp’s optimal cold-spot temperature. Moreover, the lamp is mounted transversally in the projector’s optics so as to remain horizontal at all beam directions, which garantees a constant operating temperature critical to achieve a stable light color output (the lamp is rated for an operation at ±15° from horizontal).

Osram’s HMI became so successful in their applications that a number of manufacturers began releasing their own variants of the rare-earth filled arc lamps from the 1980s onwards. Although Philips briefly sold a 575 W MSI filled with a Na-Tl-In-Dy iodide mix in the early 1970s, the Dutch did not develop the technology further and concentrated on lamps filled with tin halide (SN) and sodium, thallium and indium iodides (CSI). When it became clear that Osram’s technology was superior, Philips began releasing compatible rare-earth filled MSI lamps in 1985. Initially, they ranged from 200 to 4000 W and all models except the 1200 W MSI were outsourced from Osram. This practice continued for a few years until Philips developed a full production capacity at its HID mother factory in Turnhout, Belgium. The MSI 200 W featured here is representative of this transitional period as it was made by Osram in Berlin (West Germany, at the time).

While this lamp was a major breakthrough in portable lighting technology, it has several drawbacks such as a relatively long run up time due to a limited power load, its rare earth fill chemistry, and an exposed burner. Also, this particular lamp design did not allow power dimming to extend battery life further, while its transversal placement in the luminaires’s reflector limits the system's optical efficiency and causes too much spill light. These limitations were eventually resolved with successive developments in short-arc lamp designs, eventually resulting in the single-ended double-jacketed MSR 200W released by Philips in 1990.