Development of planar type mercury-free lamp excited by microwave surface wave plasma

This paper reports on obtaining a homogeneous and high luminance plasma to be applied as a planar type lamp for general purposes. Microwave frequency of 2.45 GHz was fed into the discharge chamber through a slot antenna facing to the rear quartz window. Xenon gas was filled at pressure range from 0.5 Torr to 5 Torr with 300 W of input power. A few types (transverse, inclined, longitudinal) of slot antennas have been tested and discharge uniformity is evaluated. Plasma is diffused at xenon pressure of 1 Torr and below whereas getting constricted at 5 Torr. The window (front or rear) was coated with a three-color phosphor of the mixture of R, G, B phosphors. Their discharge uniformity, optical characteristics and luminance are discussed. Homogenous discharge has been observed using longitudinal slot and by coating a phosphor at the rear window phosphor excitation improves resulting relatively high luminance up to 5000 cd/m
²
. Xenon pressure (below 0.5 Torr) and phosphor coating condition (mixed ratio, thickness) optimization is believed can improve the luminance as well as luminous flux.