An electrodeless plasma lamp and a method of generating light are described. The lamp may comprise a lamp body including a dielectric material having a relative permittivity greater than 2. A lamp drive circuit is coupled to the lamp body and configured to provide radio frequency (RF) power to the lamp body. A bulb containing a fill is positioned proximate the lamp body. The fill forms a plasma when the RF power is coupled to the fill from the lamp body. A lamp drive circuit including modulation control circuit is provided to control modulation of a frequency of the RF power across a frequency band. The circuit may be configured to provide RF power across a frequency band around a resonant frequency for the lamp body to reduce peak amplitude and electro-magnetic interference while maintaining average power to the plasma.