RF/Microwave Discharge Plasma for Mercury-Free Lighting

This research focused on the development of a mercury-free light source through the use of radio frequency (RF) and microwave discharges. RF at 13.56 MHz and microwave at 2.45 GHz were applied to generate the plasma. With the use of this kind of high frequency power generator, plasma can be ignited without using the electrodes inside the chamber or discharge tube, which could significantly increase the lamp lifetime. The potential for high luminance, excellent colour rendering and environmental-friendliness makes xenon the most promising candidate as the replacement for the mercury fluorescent lamp. In this research, RF energy at 13.56 MHz was induced to the cylindrical discharge tube in order to investigate the characteristics of the xenon RF-inductively coupled plasma discharge as a light source. The luminance, spectral distribution and colour rendering index were measured. The values of the luminance and colour rendering index were comparative to the values for a conventional discharge lamp. For microwave plasma, in order to develop a planar-type lamp, surface wave plasma was applied. A few types (transverse, inclined, longitudinal) of slot antennas were tested and the lamp brightness and discharge uniformity were evaluated. The chamber window (front or rear) was coated with a three-colour phosphor from the combination of red, green and blue phosphors and the excitation effect was investigated. From phosphor coating and slot structure optimisations, lamp luminance and discharge uniformity could be improved.