Cathode fall voltage relationship with fluorescent lamps

A fluorescent lamp's life is greatly affected by the amount its emission mix sputters, not only during the starting process, but during the normal operating mode as well. One way to determine the amount of sputtering damage is to monitor the cathode fall voltage conditions. This report examines an external cathode fail measurement technique used with fluorescent lamps to measure this important metric Some of the basic relationships explored involve cathode fall voltage changes as a function of cathode heat voltage, ambient temperature, fill pressure, are current, current crest factor, and proximity effects due to local electric field interference. The results are taken from F40 T12, F32 T8, and F40/TT lamps. Understanding this cathode fall metric is particularly useful to lamp and ballast designers because it can be a useful indicator in estimating the sputtering damage to lamp electrodes' emission mix.