Microwave generated plasma light source apparatus

A microwave generated plasma light source apparatus comprising:

• a microwave generator;
• a microwave cavity having a light reflecting member forming at least a portion of said cavity, said microwave generator being coupled through a feeding opening in said cavity to said cavity;
• a member transparent to light and opaque to microwaves disposed across an opening of said cavity opposite said feeding opening;
• a waveguide for guiding microwaves generated by said microwave generator to said feeding opening of said cavity;
• and an electrodeless discharge bulb disposed at a position in said cavity such that said cavity operates as a resonant cavity at least when said bulb is emitting light, said bulb encapsulating at least one discharge light emissive substance and having a shape and being sufficiently small that said bulb functions substantially as a point light source, said bulb being made of transparent quartz glass and having an inner diameter such that a ratio of an outer surface area of said bulb to the microwave input power is from 1.5 mm.sup.2 /W to 15 mm.sup.2 /W, the weight of said bulb with respect to the microwave input power being no more than 3.0.times.10.sup.-2 g/W, said microwave generator comprising means for generating microwaves intermittently with a rest interval of no more than 5 msec.