MEASUREMENT OF MERCURY BOUND IN THE GLASS ENVELOPE DURING OPERATION OF FLUORESCENT LAMPS

Mercury vapor is essential to the high efficiency conversion of electrical power to light in fluorescent lamps. However, the amount of mercury that must be added to the lamp to achieve a 20,000 h operating life is much larger than the amount of vapor needed for the discharge. This is a result of processes that bind the mercury during lamp operation and make it unavailable as mercury vapor. As part of an effort to determine the amount of mercury that must be added to standard GE F40T12 lamps with halophosphate phosphors we have measured the mercury bound in the soda-lime glass under the phosphor in the positive column in a series of these lamps. From these measurements we have developed an empirical model which describes the amount of mercury per unit area that is bound in the glass as a function of operating time and the weight of phosphor over the glass.