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)

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UHP lamp systems for projection applications

Elliptical reflectors are widely used in illumination engineering as a means to concentrate the light of a source in the secondary focal plane. To collect as much light from the source as possible, the reflector must cover a wide angular range of the emitted radiation, hence forward and backward reflections on the reflector must be discussed and conditions for paraxial optics do not apply. We develop a framework of relations that describe the image of an extended source in the secondary focal plane of the ellipsoid. After deriving basic relations between object and image spaces, the propagation of rays depending of their origin and on their direction is investigated. As a result, the function and the aberrations of the reflector can be expressed in terms of an angular dependent magnification for longitudinal and lateral coordinates. With that, one cannot not only calculate luminance and illuminance distributions in the secondary focal plane in a straightforward manner, but can easily understand their properties and their dependence on ellipse parameters. On the basis of the developed relations, implications for the design of "elliptical" short arc high-intensity-discharge (HID) lamps for video projection are discussed.

Optical properties of elliptical reflectors

The present invention provides an enhanced polarized light source for a display system. In one embodiment, the invention includes a light source (11) to produce light having multiple polarization states, a relay optical system (23) to relay light imaged onto the relay optical system onto a display (17), an optical imaging element (25) to image light from the light source onto the relay optical system (23), a polarization separator (34) to direct light of a first polarization to a first portion of the optical imaging element and light of a second orthogonal polarization to a second portion of the optical imaging element, and a polarization conversion element (35) between the optical imaging element and the relay optical system to receive light having the second polarization from the optical imaging element and convert its polarization to the second polarization.

Polarized light source system with dual optical paths

A new class of compact high-definition electronic projection systems has emerged that are based on microdisplays. Very large scale integration process technology is adapted to fabricate the three classes of microdisplays: (1) transmissive liquid crystal on high-temperature polysilicon/quartz; (2) microelectromechanical devices on silicon; (3) and reflective liquid crystal on silicon. A variety of system architectures are discussed. Key ancillary technologies include small arc lamps, color separation and recombination optics, and rear-projection screens.

Progress in projection and large-area displays

Projection engine designs are mostly based on discrete optical components including color filters, mirrors, relay lenses, prisms, etc., which tends to be expensive and increase the space requirement. With the advancement of light pipe based illumination system, e.g. the Wavien patented dual paraboloid reflector system, and light-pipe based polarization recovery system, it would be advantage to design a light-pipe based projection engine for a complete light-pipe based system for low cost and space saving applications. In this paper, a totally light-pipe based projection engine is described. It consists of an etendue efficiency illumination system using the dual paraboloid reflector system with a lensed tapered light pipe as the output. The output is then directed into a light-pipe based polarization recovery system such that the output is polarized. The polarized light is then separated into its individual RGB colors, and is directed into the corresponding HTPS imager chips separately by the use of light pipes, prism, and beam splitters. The outputs from the imager chips are then recombined by an X-cube and projected onto the screen. This light-pipe based system uses low cost optical components and take up much less space than the traditional projection system.

Novel Projection Engine with Dual Paraboloid Reflector and Polarization Recovery Systems

New developments of UHP lamps with higher power and shorter arcs (even below 1mm) fulfill the optical demands of future projectors and novel displays. In addition a new technology is presented which leads to a reduction of the lamp ignition voltage from 20kV to 5kV. This enables a further step in system size reduction.

52.1: Invited Paper: New Developments in Projection Light Sources—Shorter Arcs and Miniaturisation

UHP-lamps are standard for high efficient projection systems. All short arc lamps show arc instabilities. Optical integrators can successfully suppress visual effects but they are of limited use for small displays. A new technology is presented here which stabilises the lamp arc directly and keeps the good maintenance of the lamp.

G. Derra

Papers

52.1: Invited Paper: New Developments in Projection Light Sources—Shorter Arcs and Miniaturisation

9.1: Arc Stabilisation for Short Arc Projection Lamps