Mid-1990s Philips MSR 4000 HR

Philips's MSR is the first compact jacketed rare earth halide arc lamp released on the market. The Dutch developed this high-performance source during the 1980s specifically for stage and studio floodlighting applications. To this end they replaced the tin halide fill chemistry of their SN lamps by one based on rare earth additives (primarily dysprosium). Since this change resulted in a very significant increase in efficiency, the lamps were re-rated to higher wattage levels. The SN 250W, 500W and 660W then became the MSR 400W, 700W and 1200W, which where first introduced at Photokina (Cologne, FRG) in 1988. A 2500 W MSR based on the SN 1000W was added the following year.

While compact arc sources filled with rare earth halides were not a new technology (Osram first introduced them in 1967), it was the first time these were used enclosed in an outer jacket. This addition no only permits much shorter burner end seals (thanks to the protective gas fill), this also changes the lamp's thermal balance in such a way that it became possible to reduce the input power by 60 % while maintaining excellent light color properties with little change in color temperature (also a characteristic of SN lamps). This particular feature and their single-ended configuration thus made MSR lamps much more flexible than conventional rare-earth lamps of the double-ended design.

MSR lamps were an instant success and Philips released an hot-restrike version of the original models in 1989. For several years the MSR 2500W was the largest type available. Because there was no larger existing SN lamp platform available to quickly release a more powerful MSR, it took three years for the Dutch the develop a 4000 W source from scratch. This lamp was eventually introduced in 1992 and remained the largest MSR lamp produced at Philips's HID lamp factory in Turnhout, Belgium.

The lamp shown here is not standard, it is a special development model built several years after the 4-kW type introduction, for the purpose of testing some design changes, like the addition of a metal support clip at the lower end of the arc tube in order to better center it. Interestingly the bulb is filled with a N2-CO2 mix instead of the usual nitrogen atmosphere. There are two possible advantages to the addition of carbon dioxide: to keep the lamp clean through life thanks to a slightly oxidizing atmosphere (CO2 releases oxygen upon thermal decomposition at the burner), and to prevent internal flashover (CO2 has a higher dielectric strength than N2). The latter is most likely to have been the scope of the investigation because the standard 4 kW MSR is usually provided with a quartz tube sheathing the side frame wire and fused with the bulb pinch, precisely to prevent flashover at the seal. This feature is clearly missing in the present lamp. Except for these changes, the lamp is pretty much identical to the standard one that was produced at Turnhout.