Effect of the auxiliary external electrode on xenon fluorescent lamp depending on its diameter

Summary form only given. Since the environmental awareness is increasing, the development of a high efficacy mercury-free fluorescent lamp is strongly required. Although the xenon is one of the most promising candidates for substitution of mercury, its discharge tends to constrict and the efficacy drops drastically at high input power. The authors have developed a technique to enhance the total flux and the efficacy of the cold cathode xenon fluorescent lamp by using an auxiliary external electrode (AEE); it has an effect to expand the positive column and suppress its constriction. Since that effect is attributed to the electrical coupling between the positive column and the AEE, it is easily expected that the effect of the AEE depends on the lamp diameter. In this paper, the effect of the AEE on the power consumption and the efficacy depending on the lamp diameter is studied. The lamps with three different diameters were prepared: 14, 27 and 32 mm in outside diameter. The lamps have two inside electrodes for cold cathode discharge with 50 mm separation. The AEE made of aluminum tape with 3 mm wide is wound on the outside of the lamp near the HV (high voltage) side electrode (cathode), i.e. 5 mm from the cathode and 45 mm from the anode. The AEE is grounded through a resistance between 5 kOmega and 10 MOmega. The xenon filling pressure was set at 2.7 kPa. The inside wall of the lamp bulb was coated by three band phosphor emitting white luminescence. The lamp was operated by pulsed discharge with frequency of 30 kHz and pulse width of 3 mus. As a result, in the all three diameter cases, the maximum input power without positive column constriction increased by using the AEE. Moreover, maximum total flux was enhanced as well. Thus, the efficacy was improved in the all three cases. The highest efficacy was achieved in the small diameter case (~33 lm/W, 014 mm), whereas the highest efficacy improvement by the AEE was achieved in the middle diameter case (-10%, 027 mm). - hus, it is shown that the optimum condition for the lamp diameter exists to obtain the highest AEE effect. The discharge propagation observation with an ICCD camera and the electrical field calculation are under progress and their results and discussion will be presented.