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Special issue on light sources

This special issue of Journal of Physics D: Applied Physics covers some of the applied physics currently being addressed by light source researchers. Most of these papers originate from presentations made at the 10th International Symposium on the Science and Technology of Light Sources, held in Toulouse, France, on 18--22 July 2004. The conference attracted about 400 participants from all over the world. Abstracts of all papers, including extended abstracts of invited papers, were published in the conference book Light Sources 2004 (Institute of Physics Conference Series 182) edited by G Zissis. The full papers published in this issue reflect the wide-ranging nature of research on light sources. These collected full papers survived our rigorous journal review process and they report completed, previously unpublished, pieces of work. This is a research field that has seen many major contributions over the last hundred years; nevertheless it continues to produce new sources and important improvements to existing types. It is evident from these papers just how crucial are the materials used for light sources. Numerous recent lamp developments have depended critically on new or improved materials. Ten or more of the papers are concerned explicitly with materials: for example, an environmentally important and challenging area of research is to find a viable alternative to the use of mercury, particularly in fluorescent lamps. This is difficult because a substitute for Hg in general lighting must match the remarkable efficiency of Hg, or risk doing harm to the environment through increased energy consumption. Large-scale computation of the properties of both high- and low-pressure discharge lamps has become indispensable. A good example is in the paper by Derra et al, which is the first major review of an important lamp type. The lamp of interest is a mercury arc used in data projectors, operating with an arc gap of approximately 1 mm at more than 100 bar pressure. Most of the information needed for design is not accessible experimentally. Computer models were essential tools in many aspects of development, including finding out how the highly stressed materials could be used in ways that ensured acceptable life. Short-arc metal-halide lamps are used for producing white light in commercial premises, but they present numerous challenges to developers. Exceedingly complex chemistry, the many emitters and absorbers, the lack of symmetry, and the increasing influence of electrodes as the arc is shortened—all these pose many design problems that are being tackled with increasing success with the help of computer models. This special issue has many papers that deal with electrode issues, with special emphasis on the experimental verification of model predictions. Radiation transport also continues to be a major issue in constructing realistic discharge models. A number of papers tackle this in a simplified manner, whilst a new ray-tracing scheme offers hope of a realistic calculation of radiation in the complicated short-arc metal-halide lamps mentioned above. Light-emitting diodes are now having a major impact on some areas of lighting; two papers in this issue reflect that trend. The group of papers in this special issue will surely provide an important resource for those researching new and improved lamps.