Improving Luminous Efficacy of Ceramic Resonator Plasma Lamps by Using Microwave Pulse Modulation

The microwave plasma lamp is an electrodeless light source that uses radio frequency (RF) energy to excite gas discharge. By using the square wave pulse modulation, this article studies the luminous characteristics of the rectangular ceramic resonator plasma lamp so as to improve the system’s luminous efficacy. When the modulation frequency is 22 kHz and the duty ratio is 90% for a quartz bulb with color rendering index (CRI) of 92, the luminous efficacy can be increased by 15% steadily for the RF power of 180 W. The spectral power distribution is almost the same as the continuous wave (CW) 200 W, indicating that the luminous efficacy is improved without changing the luminous parameters and performance. The luminous flux is very sensitive to different modulation frequencies during the arc discharge state. This sensitivity is explained by the resonance between the pressure wave generated by pulse modulation and the reflected wave from the tube wall. Finally, the luminous efficacy of 90.4 lm/W for the light source and 60 lm/W for the system is achieved. This study provides a method to increase the luminous efficacy when the efficiency of the RF driver cannot be significantly improved, and it has a practical value to prolong the life of plasma lamps.