An embodiment of a system includes an RF signal source, a first electrode, a second electrode, and a cavity configured to receive an electrodeless bulb. The RF signal source is configured to generate an RF signal. The first electrode is configured to receive the RF signal and to convert the RF signal into electromagnetic energy that is radiated by the first electrode. The cavity is defined by first and second boundaries that are separated by a distance that is less than the wavelength of the RF signal so that the cavity is sub-resonant. The first electrode is physically positioned at the first boundary, and the second electrode is physically positioned at the second boundary. The first electrode, the second electrode, and the cavity form a structure that is configured to capacitively couple the electromagnetic energy into the electrodeless bulb when the electrodeless bulb is positioned within the cavity.