Achim Gerhard Rolf Koerber

UHP lamp systems for projection applications

Projection systems have found widespread use in conference rooms and other professional applications during the last decade and are now entering the home TV market at a considerable pace. Projectors as small as about one litre are able to deliver several thousand screen lumens and are, with a system efficacy of over 10 lm W −1 , the most efficient display systems realized today. Short arc lamps are a key component for projection systems of the highest efficiency for small-size projection displays. The introduction of the ultra high performance (UHP) lamp system by Philips in 1995 can be identified as one of the key enablers of the commercial success of projection systems. The UHP lamp concept features outstanding arc luminance, a well suited spectrum, long life and excellent lumen maintenance. For the first time it combines a very high pressure mercury discharge lamp with extremely short and stable arc gap with a regenerative chemical cycle keeping the discharge walls free from blackening, leading to lifetimes of over 10 000 h. Since the introduction of the UHP lamp system, many important new technology improvements have been realized: burner designs for higher lamp power, advanced ignition systems, miniaturized electronic drivers and innovative reflector concepts. These achievements enabled the impressive increase of projector light output, a remarkable reduction in projector size and even higher optical efficiency in projection systems during the last years. In this paper the concept of the UHP lamp system is described, followed by a discussion of the technological evolution the UHP lamp has undergone so far. Last, but not least, the important improvements of the UHP lamp system including the electronic driver and the reflector are discussed. (Some figures in this article are in colour only in the electronic version)

UHP lamps for projection systems: getting always brighter, smaller, and even more colorful

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.

Infrared continuum radiation from high and ultra-high pressure mercury lamps

Infrared (IR) continuum radiation from the arc of high and ultra-high pressure (UHP) mercury lamps was measured and modelled. Three major contributions to the IR continuum are electron-atom bremsstrahlung, which is dominant, electron-ion bremsstrahlung and electron-ion recombination radiation. The line width of the resonance broadened Hg 7 1 S 0 to 6 1 P 1 transition at 1014 nm was used to determine the arc core Hg density, and the radiance of this line was used to determine the arc temperature as a function of radius. The temperature map for the UHP lamp was checked using the Bartels method on the 546 nm line of Hg. Model results based on recently published electron-atom bremsstrahlung coefficients were found to be in good agreement with measurements across the near IR.

Novel Molecular Discharge Light Sources

A systematic investigation into transition metal halides and oxides showed the high potential of transition metal oxides as visible radiators for highly efficient gas discharge light sources. Zirconium monoxide (ZrO) has been identified as the most promising candidate combining highly attractive green and red emission band systems with very high dissociation energy (8.2 eV) which ensures that the molecule is stable even at the hot plasma centre. Thus far, however, it has been impossible to keep ZrO in the gas phase of a closed discharge vessel, because at wall temperature usually compounds are formed which have negligible vapour pressures. We succeeded in establishing a regenerative chemical cycle by filling ZrX4 (X = Cl, Br, I) together with a stable, but volatile oxygen compound (like MoO2X2) and realized thus highly attractive, novel gas discharge light sources.

16.1: UHP Lamps with Increased Efficiency

Shorter arcs and higher gas pressures increase the collection efficiency and produce a spectrum which is ideal for video projection. Taking into account the physical lamp efficiency ideal arc lengths are given. New UHP products will realise 30% more light on the screen.

Measuring the pressure in ultrahigh-pressure mercury arcs

Ultrahigh-pressure (UHP) mercury lamps are important as high-brightness light sources for digital projection. Hg pressures are usually above 20 MPa and difficult to measure. We have built special UHP lamps with a liquid Hg condensate in a temperature-controlled reservoir, allowing us to tune the Hg vapor pressure p between 14 and 30 MPa. As a simple measure for p, we recorded the width Δλ of the 546 nm Hg line while varying p and also the lamp current I and voltage U. The data define a function p(Δλ,I,U) that will deliver p to better than 3% from simple measurements of Δλ, I, and U for most UHP lamps in the important 100–200 W power range. The method is applied to sample lamps, yielding pressures up to 26 MPa and demonstrating how filled Hg amount, burning position, arc gap, and lamp power affect the pressure. The effective temperature of typical UHP lamps is found to be 2400 K. We also derive an improved characteristic U(d,p,I) for the dependence of the arc voltage on arc gap, pressure, and current for e...

Advanced UHP lamps for projection systems

Projection systems for large screens have made tremendous progress during the last years, both in terms of performance and size reduction. Improved UHP lamp systems made a major contribution to enable the new generation of projectors. The arc gap is reduced to 1 mm only and allows a high collection efficiency in the projector. At the same time the lamp wattage was increased. In this way, todays projectors can create high-quality XGA pictures with more than 3000 screen lumens using one single 200 W UHP-lamp. Such a projector reaches an efficiency of more than 10 screen lumens per watt electrical input power. The volume of lamp and driver has been reduced by one order of magnitude during the last six years. This was possible by recent progress that has been achieved on the ignition of the lamp. By using a UV-enhancer cavity in the lamp seal and an additional antenna the ignition voltage could be reduced from 20 kV to below 5 kV. This allows more compact drivers and is ideal for miniaturizing projectors. A new optical concept allows for extremely compact reflector systems: A dichroic coating applied to one half of the UHP burner focuses all light into one hemisphere. Additionally 20-30% more light can be collected in systems with high optical demands. Making use of both the reduced ignition voltage and the new optical concept a reduction of the volume of lamp and driver by a factor of 10 has been realized.