Diagnostics of lighting plasmas

Summary form only given. The author discusses current experimental techniques and on Plasma Science strategies for the diagnostics of the physicochemical properties of lighting plasmas (light sources). The configurations and compactness of commercial light sources, display panel backlights and cells, etc., and the materials used in their construction, pose interesting challenges for diagnostic measurements. Their generally small size and the fact that they are closed systems does, however, at least offer the important advantage of making them laboratory convenient. As might be anticipated, light sources are by their very nature accessible to investigation using an array of optical and spectroscopic techniques, particularly laser based techniques, and these can provide precise spatio-temporal information on the most important plasma parameters such as species identity, number density, temperature, flow velocity and electric field. The scope and general capabilities of these techniques with respect to lighting plasmas will be reviewed, with emphasis being given to studies of operating lamps. Challenges and opportunities for future work will be highlighted. Included in the review also will be discussion of techniques that can probe in a non-destructive manner the physical and chemical properties of surfaces (e.g., envelopes, electrodes) that bound lighting plasmas. Studies of these plasma-materials interfaces are of great interest and importance in lamp diagnostics generally because of their close relation with key longer timescale issues relating to the technology itself such as lamp failure mechanisms and life. Modelling and simulation of many key lighting plasmas is relatively well advanced compared with many other areas of plasma science and technology. This has resulted in a powerful synergy between measurement and modelling and examples of how this has advanced understanding will be highlighted. Another important feature of current light source science and techn- logy that impacts diagnostic measurements is the treatment of lighting plasmas and their power supplies as integrated systems. Until recently the inclusion of plasmas as circuit elements into otherwise well developed circuit modelling tools such as Spice has been primitive, e.g., being represented as a simple resistor. This situation is changing rapidly and models with explicit inclusion of the plasma physics are being developed which are able to predict V-I characteristics with some success. These new systems based tools are proving important in the interpretation of diagnostic measurements on pulsed operation lighting plasmas which promise useful increases in efficacy in comparison with equivalent plasmas operated in conventional DC and AC modes.