A plasma lamp including a waveguide body consisting essentially of at least one dielectric material having a dielectric constant greater than approximately 2. The body is coupled to a microwave power source which causes the body to resonate in at least one resonant mode. At least one lamp chamber integrated with the body contains a bulb with a fill forming a light-emitting plasma when the chamber receives power from the resonating body. A bulb either is self-enclosed or an envelope sealed by a window or lens covering the chamber aperture. Embodiments disclosed include lamps having a drive probe and a feedback probe, and lamps having a drive probe, feedback probe and start probe, which minimize power reflected from the body back to the source when the source operates: (a) at a frequency such that the body resonates in a single mode; or (b) at one frequency such that the body resonates in a relatively higher order mode before a plasma is formed, and at another frequency such that the body resonates in a relatively lower order mode after it reaches steady state.