A study of HID lamp life when operated by electronic ballasts

The pursuit of making more effective use of the attractive features of compact metal halide lamps has recently promoted further development of electronic ballasts. One of the typical designs of such electronic ballasts was reported by H. Nishimura, et al. at the IESNA Annual Conference in 1987. Generally, when a lamp is operated with a conventional inductive ballast, the output characteristics (lamp wattage vs lamp voltage) are determined uniquely by a given power supply voltage. On the other hand, in the case of the electronic ballast, output characteristics can be freely set up. Using 150-W compact metal halide lamps, we have experimentally verified that the output characteristic, when controlled by an electronic ballast, has a significant influence on the life of the lamp. If output characteristics are controlled by an electronic ballast to have the same characteristics as a conventional inductive ballast, the lamp life was found to be shorter than regular operation with the conventional ballast. We have found that the cause of this phenomenon comes from the localized temperature difference on the surface of the are tube, comparing operation by a conventional ballast vs an electronic ballast. The temperature difference appears to be caused by the difference in the power factor of the lamp. Based on the analysis of this phenomenon, we achieved improved lamp life by controlling the output characteristic to keep the localized temperature differences on the are tube within certain limits.