Characteristic improvement of inductively coupled electrode-less metal halide lamps

Inductively coupled electrode-less metal halide lamps were expected to show high efficacy and good life performance and had been studied extensively. At first, at LS6 in 1992, a new inductively coupled HID lighting system was proposed. Since that, improvement of operating circuit efficacy and operation stability of the system has been discussed by using the current limitation of the co-axial cable for impedance matching circuit. On the other hand, dosing tin halides in those arc tubes was tried to extend their life. In this study, to put these systems into practical use, improving lamp efficacy, confirming effect of tin halides on their life performance and improving their operation stability by decreasing Q value, which is resonance constant of their impedance matching circuit, were attempted. As a result, the lamp efficacy reached to 180 lm/W with white color and 58% of visible radiation power ratio to the input power was realized by optimizing rare gas pressure, input wattage, a sort of doses and by employing the elliptical-shape outer jacket with uniform temperature distribution on the arc tube surface. Their life performance was confirmed that the lamps with tin halides were abler to survive up to 60000 hours at rated load operation without decreasing lumen output, because tin halides absorb iodine gas generated in the arc tube and prevent ulit problem. Optimizing the distance between the coil and the arc tube, the arc tube diameter and the rare gas pressure, Q value was decreased by 22% without reducing their lamp performance.