Abstract: A luminaire has a light source in the form of a quartz crucible, having a plasma void. A power supply has a magnetron for providing microwaves for generating a plasma in the void. An air wave guide is connected below the magnetron and a connector is connected below the wave guide. The plasma crucible is fitted to the bottom of the connector and is enclosed by a Faraday cage. Arranged with the crucible at its focal point is a reflector. It has a central aperture through which the connector extends. A lower, hemispherical shell of a casing for the power supply supports the reflector at a similar aperture, with the interposition of one or more focus adjusting spacers.