A Lamp Life Predictor for Frequently Switched Instant-start Fluorescent Systems

ABSTRACT Although T8 fluorescent lamp life is typically rated at 20,000 hours, it can significantly vary depending on the ballast product. The current industry practice for testing fluorescent lamp life requires these lamps to be subjected to 3-hours on/20-minutes off cycle, which is also known as the standard cycle for life testing. This method requires over 2 years of testing, which is expensive and also delays the development of new products. Therefore, researchers have been trying to expedite the procedure for lamp life testing by increasing the switching frequency. However, none of these attempts have shown much promise for correlating the lamp life on faster cycles to the lamp life on the standard cycle. Alternatively, researchers have been trying to correlate certain starting and operating electrical parameters of the lamp-ballast system to lamp life. As an example, it has been shown that the ratio of the hot cathode resistance to cold cathode resistance correlates well with lamp life for rapid-start ballast fluorescent systems. Instant-start ballasts comprise a larger market share than rapid-start ballast. A literature survey shows that at the present time there is no such parameter available for predicting lamp life of instant-start systems. It is also shown in literature that within a range, lamp life shortens with increasing switching frequency. At very fast switching frequencies such as the 5-minutes on/5-minutes off cycle, the major portion of the electrode damage takes place due to starting, which ultimately leads to lamp failure. At standard operating cycles, the electrode damage takes place during starting and operating periods. To predict lamp life on any switching cycle, one has to know the amount of electrode damage that takes place due to starting and the amount of electrode damage that take place due to normal operation. This study deals only with starting effects. The goal of this initial study is to analyze the starting electrical properties and identify a parameter that correlates well to high-frequency switching life, which provides insight to the amount of electrode damage that takes place during starting. It is shown here that the time integrated value of the lamp voltage over the starting