Lifetime control of fluorescent lamps
Publication Date: 2005-Jun-29
The IP.com Prior Art Database
Lifetime control of fluorescent lamps.
The lifetime of fluorescent lamps is controlled by depletion of the emitter material from the lamp electrodes. This depletion takes place during stationary burning of the lamp, but also more in particular during ignition when a very high ignition voltage is present between the lamp electrodes causing sputtering of the emitter material. As a consequence the lifetime of the lamp strongly depends on the number of times it is ignited. In practise this is undesirable since it makes the lifetime of the lamp strongly dependent on its particular application and therefore unpredictable. However, it is possible to construct and ignite the lamp in such a way that its lifetime becomes independent from the number of times it is ignited. For this purpose one of the electrodes is covered with much more emitter material than the other. These electrodes are respectively referred to as the lifetime non-controlling electrode (LNCE) and the lifetime controlling electrode (LCE). By clamping the ignition voltage in one direction making use of a series arrangement of a diode and a zener diode it is ensured that the ignition voltage reaches an amplitude high enough for lamp ignition, only when the LNCE is the cathode of the lamp. The emitter material depletion by sputtering thus only takes place on the LNCE. Both the LNCE and the LCE lose some emitter material during stationary operation. The LCE thus only loses emitter material during st...