Charging Tendency of Phosphors and Blackening Phenomena in Fluorescent Lamps.

Abstract

Long-term lumen maintenance of high-load fluorescent lamps is investigated using 3-band rare earth phosphors. The contact electric charging tendency of the phosphor is systematically varied by depositing colloids on the phosphor particle surfaces. For every phosphor system tested, the maintenance shows a maximum at a certain value in the charging tendency where the amount of mercury oxide absorbed on the phosphor is minimum. On the other hand, the depreciation of the phosphors themselves does not depend on the charging tendency. Furthermore, the charging tendency of mercury oxide exists near that for maximum maintenance. From these results, it is concluded that the difference in charging tendency between mercury oxide and a phosphor governs mercury oxide adsorption on the phosphor; the amount of adsorbed mercury oxide becomes larger with an increase in the difference causing significant lamp depreciation.