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Methods were investigated to improve the lamp characteristics of inductively coupled electrodeless metal halide lamps to make them practical. First, evaluating lamp efficacy by adjusting the lamp parameters showed that a lamp efficacy of 180 lm/W (Including coil loss: 151lm/W) white color could be attained. Second, the conditions generating free iodine and bulb deterioration, the main factors limiting the life of these lamps, were investigated. For long-life-type lamps, which had 130 lm/W of lamp efficacy, the lamp lumen level did not decrease during 21,000 hours of overload operation (corresponding to 58,000 hours of rated-load operation). These lamps thus have excellent lumen maintenance and life performance compared with conventional electrode metal halide lamps. Third, improving circuit reliability by decreasing the Q value of the resonant circuit was investigated for long-life-tpye lamps which had 145 lm/W of lamp efficacy. The relationship between the Q value and the lamp parameters was analyzed, and the Q value was decreased to 78% its value while maintaining the same lamp performance.