Physics
Scientific paper
Jul 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008jphd...41n0301w&link_type=abstract
Journal of Physics D: Applied Physics, Volume 41, Issue 14, pp. 140301 (2008).
Physics
Scientific paper
The papers in this Special Issue of Journal of Physics D: Applied Physics originate from the 11th International Symposium on the Science and Technology of Light Sources (LS:11) held at Fudan University, Shanghai, China, during 20 24 May 2007. Abstracts of all papers were published in the conference book Light Sources 2007 (Sheffield: FAST-LS) edited by Muqing Liu and R Devonshire. Special issues were produced after LS:9 and LS:10 and have proved to be well-cited and important sources of information for this community.
The Symposia occur at three-year intervals. In this one over 200 papers were presented—the majority as posters—with ample time provided for active discussion. As all submitted papers had to be refereed in the normal way for J. Phys. D: Appl. Phys., I was concerned that too many submissions would overwhelm the small number of referees available in this area. To ensure a broad spread of interests and opinions, I invited 10 senior colleagues to give me their recommendations about who should be asked to submit papers for this Special Issue. The criteria were that the work should be new, complete and within the scope of the journal. As a result of their suggestions 42 authors were asked to submit papers. Not all authors were able to submit a manuscript in time and some, at my request, combined their work into a single paper. The 28 papers published here are the result of that process.
The issue starts with a comprehensive review by Benilov of the remarkable progress that has been made in the past 15 years in understanding the behaviour of cathode and anode terminations in arcs. It is fair to say that we now have a fundamental understanding of the formerly baffling behaviour of spot and diffuse terminations, at least in the quasi-steady state. A number of following papers cover applications of this theory, extensions to time dependence and examination of the effects of the different gaseous atmospheres in which lighting arcs operate.
Mercury has very great advantages for efficient discharge lighting, including high volatility, high electron collision cross-section and its 3P levels, which are a major factor in the high efficiency generation of UV. Unfortunately, it is somewhat toxic and therefore unwelcome in the environment. Most of the mercury used in lighting is in fluorescent lamps and these produce (at high efficiency) most of the artificial light on this planet. Finding an alternative is proving a difficult but nevertheless active research field (see the recent Special Cluster on Mercury-Free Discharges for Lighting, edited by M Haverlag, in J. Phys. D: Appl. Phys. volume 40, issue 13). The other approach is to reduce the amount of mercury in each lamp. Much has already been done but pressure for further reduction continues; Corrazza and Boffito review the current status. Developments in the behaviour of fluorescent lamp electrodes and in the ignition of fluorescent lamps are amongst the papers presented on this most important discharge.
Major advances in the performance of LEDs have been made in recent years, although currently most LED lighting is used for signalling and decorative lighting; this is because LEDs cannot yet produce the light levels needed for general illumination at costs and efficiencies that compete with discharge lamps. Because of their specialized technology, papers from this area are somewhat under-represented in this issue. Papers on OLEDs and the specialized field of LED measurement are included.
HID (high intensity discharge) lamps operate close to LTE at high temperatures and pressures in corrosive atmospheres. Research on materials has been very important for their development and is represented here in two papers. Diagnostics of HID have been crucial to securing agreement between models and experiment in HID lamps. Two papers are presented here on the spectroscopy of self-reversed lines, which provide very reliable results in lamps that typically have relatively poor optical quality. These are followed by further papers on emission spectroscopy. Amongst other diagnostics, the use of x-ray methods has proved of great importance in lamps with diffusing ceramic envelopes. Developments and applications of this technique are reported in three papers.
Comparison of model and experiment on the behaviour of metal-halide and mercury HID arcs is covered in further papers with particular emphasis on instabilities and the interaction of diffusion and convection in the flows. The understanding of breakdown and ignition of HID lamps—so critical to reliable operation—has made substantial progress as exemplified by the final two papers.
Many other interesting posters on these subjects and others were presented at the LS:11 meeting. I hope when some of this work is brought to a conclusion that it will also be published. Discharge lamps still provide the best combination of high luminous flux and efficiency for illumination. In the next few years it will be interesting to see how strongly this position will be challenged by the rapidly improving solid state light sources.
My task in preparing this Special Issue would have been impossible without the help of my unnamed colleagues who spent considerable time and energy in short-listing possible papers; they know who they are and I am extremely grateful to them.
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