120 and the gap between the two is part of the design variables that serve to tune the optimal operating frequency of the lamp those skilled in the art will recognize that the cross section may be of many shapes but ease of manufacturing would make a circular cross section preferable while avoidance of high electromagnetic field concentrations that may lead to arcing would make cross sections with sharp features undesirable one end of the output coupling element 120 is grounded to the body 600 as depicted in fig1 at point 605 the top of output coupling element 120 closely receives and is in intimate contact with gas fill vessel 130 which when excited by the electromagnetic field near the output coupling element 120 forms a radiant plasma filament 115 the gas fill vessel is a bulb made from materials such as quartz or transparent translucent alumina and contains an inert gas such as argon as well as a light emitter consisting of materials such as mercury sodium dysprosium sulfur or a metal halide salt such as indium bromide scandium bromide thallium iodide holmium bromide cesium iodide or other similar materials or it can simultaneously contain multiple light emitters the output coupling element couples the rf energy to the gas fill vessel ionizing the inert gas and vaporizing the light emitter resulting in intense light emission from the bulb a slight depression corresponding to the shape of bulb 130 may exist at the top of output coupling element 120 to positively receive the former a thin layer of high temperature dielectric material such as alumina may be configured with an adhesive to enhance the mechanical interface in certain embodiments the dielectric material may also act as.