Effect of Operating Frequency on Plasma Characteristics of Inductively Coupled Electrode-less Lamp

To increase the efficiency and lumen output of inductively coupled electrode-less lamps, numerous studies have attempted to reduce their operating frequency. This is because if the operating frequency is reduced, a wider range of semiconductor devices can be used that enable higher lumen outputs to be obtained from these lamps. The switching loss can be reduced thus increasing the efficiency. We investigated the relationship between the operating frequency of a 50-W electrode-less lamp and its characteristics. Operating frequencies of 13.56 MHz and 135 kHz were used. The characteristics that we investigated are its starting characteristics, the plasma characteristics (such as the temperature and density of the electrons), and its efficiency in producing UV radiation. The results show that the efficiency in producing UV radiation at 135 kHz is 7% lower than that at 13.56 MHz, and that plasmas generated at operating frequencies of 135 kHz and 13.56 MHz had different electron-density and electron-temperature distributions because of the different power input positions.