Electrodeless lamps for lighting: a review

Developments in semiconductor technology and changes in the standards for electromagnetic interference (EMI) have both been important in the recent exploitation of electrodeless discharges for use in lighting. There has been an active period of research on electrodeless discharges inside and outside the lighting industry and much of the basic physics and technology is now well understood. My purpose is to review and evaluate the progress. In the foreseeable future, the constraints on electronics and EMI likely to restrict the practical general purpose light sources to the H discharge principle in which the maintenance field of the discharge is provided by magnetic induction effects. Both low-pressure (LP) and high-pressure (HP) versions have received substantial developments, judging by the extensive patent literature. The former are based on the LP mercury rare-gas principle and the latter use a variety of metal halide doses. The major target for electrodeless technology is a high efficiency, look-alike replacement for the ubiquitous incandescent lamp. Although no version is yet available on the market, recent announcements suggest that it is imminent. Meanwhile, versions of the technology meeting more specialised market needs are commercially available.