The past decade has seen a rapid development of projection systems. Projectors as small as only a few liters in size deliver several thousand screen lumens and are, with an efficacy of over 10 lm/W, the most efficient display systems realized today. This has been made possible by breakthroughs in lamp technology, particularly by the development of the UHP-lamp. This broadband light source with its outstanding brightness and lifetimes of over 10000 hours is ideal for projection applications. In this paper we want to describe three major technological trend lines in the development of UHP-lamps over the past decade: First, there is a trend towards brighter projectors, which is fostered by a brightness increase of the UHP-lamps. At the same time, projectors have seen a dramatic reduction in size, which has been made possible mostly by reducing lamp- and driver-size by even a factor of 10. This was only possible by the development of new ignition concepts as well as new optical designs of the reflector. And finally, UHP-lamps have seen quite some improvement in color rendering by using even higher pressures and shorter arc gaps. This allows for more colorful pictures and even more efficient projector designs.
Light sources represent the input quantity for all design processes of projection and illumination systems and often there are features of the light source that are unsatisfying in the optical engineer's view. However, just as the design of an optical system may be understood and improved with the help of modeling tools, the development of a light source may also greatly benefit from physical models of the discharge. This paper tries to provide a basic understanding on how HID lamps work and how they can be modeled. This covers the major processes within the plasma discharge as well as the heat balance of the discharge within the burner and in particular the influence of the burner shape on the discharge behavior. Questions concerning the arc shape or the presence of a liquid melt at certain areas of the burner wall which are of vital interest to the optical designer will be addressed together with an assessment of the possibilities to influence these phenomena. Finally, a discussion on how and to which degree of reliability light technical properties can be obtained from a lamp model is presented.
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