| 摘要 |
PURPOSE: To stabilize discharge and keep it close to an arc tube, and to prevent the discharge from swaying and dying out if operation is conducted at a high power level, by modulating an RF signal by a frequency in an acoustic resonance band lower than RF frequencies used for exciting discharge in the arc tube. CONSTITUTION: An electrodeless high intensity discharge(HID) lamp 10 comprizes an arc tube 14 and an excitation coil 16 surrounding that. A gaseous filler composed of sodium iodide, cerium iodide, and xenon is put in the arc tube 14. An RF power generator 18 is coupled to the coil 16 via a matching network 36 and a discharge arc 20 is excited by an RF signal. An RF frequency from the power generator 18 is amplitude-modulated by a frequency close to an acoustic resonance frequency according to a signal from an acoustic modulation signal generator 80. Preferably, an amplitude of this modulation is larger than an amplitude of the RF frequency by 5% or more. Further, it is preferable that the RF frequency is between 3 MHz and 300 MHz and that the modulating frequency is 3 MHz or under. |
