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

A light source includes an discharge lamp including a first electrode and a second electrode emitting light by discharge between them, a drive unit performing a steady operation which supplies steady energy to the first and second electrodes and an initial operation which supplies energy to the first and second electrodes with an operation different from the steady operation before performing the steady operation, a determination unit determining states of the discharge lamp and a data storage unit storing plural initial power feeding conditions provided corresponding to states of the discharge lamp as examples of the initial operation and plural steady power feeding conditions provided corresponding to the states of the discharge lamp as examples of the steady operation, in which the drive unit performs the initial operation in any one of conditions selected from the plural initial power feeding conditions according to a determination result by the determination unit and performs the steady operation in any one of conditions selected from the plural steady power feeding conditions according to a determination result by the determination unit.

Light source and projector

A method and a circuit arrangement for the operation of a high-pressure gas discharge lamp (HID [high intensity discharge] lamp or UHP [ultra high performance] lamp) is described, which lamp is particularly suitable for illuminating projection displays with sequential color rendering (for example LCOS or SCR-DMD systems) with a pulsatory lamp current. Artefacts in the color rendering are avoided through the generation of at least one compensation pulse of a given amplitude and a given timing and through superimposition thereof on the lamp current.

Method and circuit arrangement for operating a high-pressure gas discharge lamp

A method of and a device for operating a gas discharge lamp which is fed with an alternating voltage or an alternating current and wherein the instantaneous power of the lamp is increased at given time intervals are used to form the electrodes. The value of an operational datum of the lamp which varies in time is continuously or discontinuously measured and the frequency of the alternating voltage or the alternating current (operating frequency) is selected in dependence on the measured values.

Method of and device for operating a gas discharge lamp

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

A circuit arrangement for operating a high pressure discharge lamp includes input terminals for connection to a supply voltage source, lamp connection terminals for connection of the lamp, and a power supply coupled to the input terminals. The power supply provides a current to the lamp in the form of successive periods of current and includes a pulse generating element for generating a current pulse superpositioned on the periods of the current to the lamp. The pulse generation element is synchronized with an image writing signal.

Circuit arrangement for operating a discharge lamp in synchronism with an image writing signal

The invention relates to a method for operating a discharge lamp 11 including two electrodes 12,13. The method comprises applying to the electrodes an alternating current ILamp. In order to improve the performance of the lamp and to increase the life time of the lamp, it is proposed that the alternating current has a direct current component DC for compensating a temperature difference between the two electrodes. The direct current component is selected more specifically such that a first electrode, which is expected to have a lower temperature than the second electrode, functions as anode for the direct current component, while the second electrode functions as cathode for the direct current component. The invention relates equally to an electronic circuit and to a software program for operating a discharge lamp correspondingly, as well as to a lighting system comprising a discharge lamp and means for operating this discharge lamp correspondingly.

Xaver Riederer

Papers

Method and circuit arrangement for operating a high-pressure gas discharge lamp

Method of and device for operating a gas discharge lamp

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

Circuit arrangement for operating a discharge lamp in synchronism with an image writing signal

Operation of a discharge lamp