1970 Philips HP 1000W

Although Philips never listed any high-wattage mercury lamps with a clear elliptical (ED) outer jacket in its product literature, this company made small series of HPL lamps without the phosphor coating for certain specific uses. The hard borosilicate glass bulb used in these lamps has a relatively high transmittance in the UV-A and -B domains, a spectral range between 290 and 380 nm in which high-pressure mercury discharges radiate most of their optical energy. This characteristic is particularly useful in reprographic and material ageing applications.

Interestingly, the HP 1000W shown here was made the year (1970) Philips upgraded the construction of its high-wattage mercury lamps with a more robust internal structure. Characteristics of this change is the conform-fit screw cap which replaced the original skirted E40 base cemented to the bulb. However, with its three-piece design and a quartz material full of hairline bubbles, the burner is typical of 1960s production. This arc tube is provided with two starting probes so as to ensure a reliable discharge ignition under the coldest weather conditions, which is not particularly critical in the intended application of this special clear model. Nevertheless, this feature was often necessary in old quartz mercury lamps, especially those with long electrode gap length, because of the lower quality grade of gases and materials employed in their production. This resulted in the accumulation of gaseous impurities inside the burner, mainly hydrogen, which impedes on ignition processes. Improvements in quality eventually resulted in the removal of the second starting probe in many cases.