Ignition of an electrodeless lamp, energized by microwave or radio frequency energy, is achieved by disposing an additive material in the lamp envelope along with the primary fill material. In a first embodiment, the additive is at least partially electrically conductive at room temperatures but non-conductive or a vapor at lamp operating temperatures. The preferred additives for this embodiment are mercury sulfide and mercury selenide. In a second embodiment, the additive is a material, such as piezoelectric crystals, that produces sparks in the envelope when the crystals collide with each other, or with other materials, in response to agitation of the envelope. The additive may alternatively build up electrostatic charge by rubbing along the interior surface of the lamp envelope when the envelope is agitated, the charge build up being sufficient to ignite the primary fill material.