The discovery of the electrodeless sulfur lamp (ESL) in the early 1990's offered a promise that the ESL might very well be "the lamp of the 21s' century" and was at the time hailed as one of the significant events in the development of lighting technology since Edison invented the incandescent lamp more than a hundred and twenty years ago [1-6]. The ESL was shown to produce white light with the luminous efficacy of more than 170 lm/W[,mvj with the color rendering index higher than 85 and the correlated color temperature near 6500K [3], and with the spectrum almost like that of natural light. The lifetime of the bulb itself is expected to be semi-permanent. Other attributes are that no mercury is used, making it environmentally friendly, that lack of electrodes prevents blackening of the bulbs, keeping the lumen maintenance constant over the lifetime of the lamps, and that no chemical reactions take place in plasma discharges, making the lifetime semi-permanent and producing little wastes, to list just a few. In spite of the great expectations, progress in the utility of the new light source has been disappointing, and research and development efforts in the new technology have been very much limited [7-10], After more than a decade since the advent of the new light source, this marvelous source of white light has become an endangered species, perhaps in part owing to lack of participation from the technical community and in large part due to an uncertainty in the competitiveness of the new technology. It seems that the technology is sound and still promising, and yet unsuccessful commercialization has sent out a negative message to the technical and business communities alike. This paper reviews the technology of what we dub as the microwave high intensity discharge (M-H1D) lamps and presents recent progress made in the advancement of the technology in our laboratory.
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