FREQUENCY-DEPENDENCE OF RF-DRIVEN SUBMINIATURE FLUORESCENT LAMP

Electrical characteristics and relative light emission have been measu red in a capacitively coupled, electrodeless, subminiature fluorescent lamp (SMFL) with a mercury-argon gas mixture. Discharge voltage and c urrent, transmitted power, total current, phase shift (between total c urrent and discharge voltage), plasma voltage, and relative light inte nsity were measured at driving frequencies of 13.56, 27.12, and 40.68 MHz. Based on these measurements, selected operational parameters are plotted iis discharge current and power and their behavior with respec t to frequency are compared. Included in these parameters are plasma d e bias and the ratio of sheath power to total discharge power. The exp erimental findings show that although the electrical characteristics ( electric field, relative light output) of the plasma body are virtuall y independent of the driving frequency, the external electrical charac teristics of the discharge (voltage, current, power, and ultimately re lative LPW) are very sensitive to frequency. The strong dependence of the external electrical characteristics to frequency occurs because th e sheath properties (which are very sensitive to frequency) generally dominate the overall characteristics of the discharge. General relatio ns between frequency and relative efficacy are demonstrated and discus sed.