Gas Discharge Lamps – A Requiem
Almost a century has passed since the introduction into the market of gas discharge lamps for general lighting in the form of fluorescent lamps, made possible by the discovery of phosphors able to convert ultra-violet (UV) light to visible light in 1924. The journey from the first fluorescent lamps to, efficient lamps producing high quality light was an exciting one for researchers, and much of the basic theory of gas discharge physics was developed by scientists during the early stages of gas discharge development. The trend for steady improvement continued through the end of last century, but the discovery of efficient blue light emitting Light Emitting Diodes (LEDs) in the 1990s provided a path for lamp efficacies undreamed of and unattainable by gas discharge sources. These “legacy” lamps will remain with us for many years, perhaps decades to come, but the overriding trend in the market is towards introduction of LEDs for most general lighting applications, due to the huge energy savings that will accompany them. There are certainly niche markets where LEDs have difficulty competing, but the general trend appears irreversible. This talk will take an affectionate and nostalgic backward look at the gas discharge research for lighting to which I have devoted much of my career. Most of the successes I have had would not have been possible without the inspiration, insight and friendship of Jim Lawler. The number of papers we have published together bears testimony to this. The talk will describe a journey along the paths we trod to understand how gases produce light, the fundamental principles involved, the experiment performed and the means of interpreting the results. Topics include studies of the negative glow, the positive column, and an extended look at “electrodeless“ fluorescent lamps and the efforts made to understand their performance. More recent efforts to produce electrodeless metal halides will be discussed, and finally a view on applications of discharge lamps in the expanding market of lighting for plant growth.