Abstract: A lamp has a solid plasma crucible 101 of polished quartz, with a flat front face 102 and a parabolic rear face 103. The front face is coated with indium tin oxide 104 to render it electrically conductive, yet transparent. In electrical contact with the ITO layer, is a platinum layer 105 on the parabolic rear. These two layers together form a Faraday cage around the quartz plasma crucible. At the focus of the parabola and aligned with its central axis is a void 106, filled with microwave excitable material 107, typically indium halide in xenon. The void is a bore in the quartz, that is sealed by means of a plug 108, the plug having been fused in place without other material by laser sealing. Alongside the void is a receptacle 109 in the quartz for a metal rod antenna 110. This is connected directly to the output 111 of a matching circuit such as the circuit 3. An adaptor plate 112 of the circuit has a contour 113 complementary to that of the rear face of the quartz plasma crucible.