This disclosure is directed to devices and methods for generating light with electrode-less plasma lamps. More particularly, the present invention provides plasma lamps driven by a radio-frequency source without the use of electrodes inside the bulb, and a pulse-width modulation device that provides RF power regulation, and related methods. The bulb comprises gaseous material with metal halides and/or light emitters that, when powered, substantially stays in an arc shape state. The switching pulse-width modulation device is operable at specific modulation frequencies, duty cycles, and durations to stabilize or control the arc state/mode, which enables consistent and high efficiencies.