RLOD#1 (05.05.2020) 1981 Philips HPI 12

The HPI 12 shown here is an experimental visible-light variant of the HPM 12, consisting of a bare HPI-T 400W burner sealed to two large ceramic end caps. Such construction results in a very compact light source with an overall length of 11 cm only. The lamp is nearly twice as small as the jacketed HPI-TD 400W/F that was used in various optical/projection applications. The much smaller HPI12 certainly permitted the use of much more compact and efficient optical systems, and/or enabled many lamps to be used in large banks for lighting applications requiring high optical flux densities. A key advantage of this particular lamp design is the lack of outer jacket which provides a direct access to the full emission spectrum of HPI burner, which contains a significant amount of UV and infrared radiation. At nominal temperature and power (1000 K cold spot and 390 W), 210 W is radiated out with 15 W in the ultraviolet, 97 W in the visible, and 98 W in the infrared. Naturally, these figures can be changed depending on the input power and operating temperature, which makes the HPI 12 quite a versatile light source, especially when used in combination with filters.

The quartz burner is of the three-piece barrel type, a typical Philips design that was in production from the late 1960s to the late 1980s. Its fill is similar to that of standard HPI-T lamps and consists of a Ne-Ar Penning mixture as the start gas, a mercury buffer, and a Na-Tl-In iodide mix as the main radiator. Condensation of salt behind the electrodes is prevented by electrode chambers coated with zirconium oxide which ensures a higher local temperature there. The operation of the burner in ambient air presents several difficulties, such as the accelerated oxidation of the moly end seals, or the gradual loss of neon. However, both processes are slow enough to guarantee an effective service life of at least a couple thousand hours at nominal power (390 W), which is significantly less than that of jacketed lamps but enough for special lighting applications.