The present invention relates generally to a radiant power transferring, light engine. Light engines according to the present invention may be employed in a range of applications, but they are particularly suitable for use in projection display systems. In many commercial applications using light, which require a target component (T) to be illuminated by a beam of a certain size, there is a physical separation between the source (S) and the target (T). The light source itself can be one, or a combination of sources which can be operated continually or pulsed, can be coherent, incoherent or partially coherent. In general they can be driven by AC or DC voltage, by chemical methods, by microwave heating or the like. Generally, the light from the source will require to be reformatted such that it is usable by the target in terms of spectral efficiency and in particular the spatial and angular matching of source to target. Most commonly, the formatting required will be in terms of beam area (cross-sectional), intensity distribution, intensity level (both maximum and minimum), incident angle when reaching target, propagation direction, spectral content and spectral distribution. These parameters can be affected by various optical components such as colour wheels (cw), light guides (LG), Polarization Converters (PC), etc. and the overall system layout can affect the overall light throughput of the system. Each individual component can be described as an effective or intermediate target component when describing the system. The light rays which are not incident on a given target are considered to be wasted and can have undesired effects on the system such as heating of certain elements, and causing undesired reflections and stray light within the system. It is useful to mask these rays or use suitable 'light sinks' to alleviate any problem with stray light rays. It is therefore desirable for any system used for the purpose such as the invention stated here that as much of the source light is utilised by the target as is physically possible. A Light Engine (LE) as defined here can be described as an apparatus that collects light from a given source or sources and reformats that light so that it can be utilised elsewhere in a given system. It is typically made up of multiple optical components that together have at least two or three major tasks. The first task is to collect light from a source S. The second task is to deliver some of the collected light to the target T. The third, and often optional, task is to reformat the light beam to enhance the usable content of the light delivered to the target T. At least in preferred embodiments, the light engine efficiently collects light from a source or sources and reformats the light so that it can be utilised efficiently. The optical parameters called etendue E, etendue efficiency EE, throughput efficiency TE and delivery efficiency DE are important in better understanding this invention and are defined and discussed below. The etendue E is a measure of both the spatial and angular confinement of a light beam. The throughput efficiency TE and etendue efficiency EE are related parameters and measure in different ways how efficiently a given optical system reformats a given input beam compared to an ideal performing optical system. The delivery efficiency DE parameter measures both the fulfilment of the target formatting requirements and the throughput efficiency of a LE for a given target T, i.e. measured the amount of both collectable and usable light by a given target T. Light engines are used in many applications and the references given here show the different methods for collection and distribution of light rays within a light engine. U.S. Patent No. 5,491,765 to Matsumoto (1996) describes a typical Light Engine design where a parabolic, sealed short arc reflector lamp, in combination with a focusing lens, is used to deliver collected energy to the entrance surface of a round fibre optic Light Guide and U.S. Patent No. 5,574,328 to Okuchi (1996) discusses a light engine which has a double concave reflector forming a light engine collection system with the source axis of a gas discharge arc lamp aligned co-linear with the optical axis of the collection system. U.S. Patent No. 5,491 ,620 to Winston et. all (1994) has a double concave reflector system as the light engine and a light guide collecting the re-concentrated light. These types of light engine are standard formats which are used extensively in lighting apparatus, car headlamps etc and do not allow for multiple sources to be used in an efficient manner. Prior art Projection Light Engines (PLE's), which are designed to illuminate a projection screen by illuminating first a Light Valve or Light Modulator, are even more complex and optically demanding than the above-discussed prior art light engines. The selection of particular optical key components for a PLE often introduces additional design constraints. U.S. Patent No. 5,592,188 to Doherty (1997) describes a typical PLE for a single digital micro mirror device (DMD) type reflective light valve. The light discussed in this patent is very similar to the one discussed in U.S. Patent No. 5,491 ,765. However, instead of illuminating a light guide, this system focuses the collected source energy onto a colour wheel, which creates a time sequenced colour beam. This application also uses only one source. The use of the colour wheel has a marked effect on the efficiency of the overall system. U.S. Patent No. 5,098,184 to van den Brandt and Timmers (1992) describe lens array designs for the spatial beam intensity homogenization in a PLE that illuminates a liquid crystal type light modulator. This type of light engine again uses a single source and reflector but uses lens arrays to increase efficiency. In order to increase efficiency of a light engine, it is important that the light from the source is collected and redirected in such a manner that a high percentage of the source light is incident on the image forming component of the system, as is suggested here for use in a projector. US Patent 6674576B1 show a method for use in telescopic communications which uses a general mirror arrangement. GB0385104A, GB0474039A and US 6356390B1 show the use of an array of light sources in an annular configuration. It is therefore an object of the present invention, at least in preferred embodiments, to provide a method for designing efficient light engines for a broad range of etendue- limited targets T. It is still a further object of the present invention, at least in preferred embodiments, to provide improved cost/performance ratio of Light Engine's for given primary and/or intermediate target demands due to reduced or minimised component count. It is still a further object of the present invention, at least in preferred embodiments, to provide improved PLE's and new types of projection display systems for truly portable projection systems. It is still a further object of the present invention, at least in preferred embodiments, to change the manufacturing of related component to improve their usability for manufacturing high efficiency light engines. It is still another object of the present invention, at least in preferred embodiments, to provide methods for reducing the size of related components and projection systems while increasing or maximizing the delivery efficiency of a related light engine or related light engines. Viewed from a first aspect, the present application relates to a light engine for the delivery and reformatting of the output of a light source, the light engine comprising: a) a light source; b) a first mirror for reflecting light from the light source towards a target, the first mirror having a first focal point; and c) a polarizer located between the first mirror and the first focal point. At least in preferred embodiments, the invention reduces the number of optical components required in the overall system and therefore helps to reduce the overall optical losses incurred due to the respective losses incurred at each optical component. Additionally, the invention allows for shrinkage of the light engine without compromising the - A -

collection efficiency of the system that could not be achieved with standard light engines currently known in the art. The simplicity of the light engine allows for a simple reformatting of the light from the source or sources that is not directly usable by the target without the need for multiple additional optical components. Consequently, the physical dimensions of the proposed light engine can be reduced whilst the amount of usable light that is delivered to the target is increased. The light source preferably comprises at least one red individual light source, at least one green individual light source and at least one blue individual light source. The RGB light sources preferably consist of light emitting diodes or laser diodes. In arrangements having only a single second mirror, an aperture may be provided in the second mirror. The light engine preferably further comprises at least one collimator for collimating the light emitted from the light source. The light emitted from the light source is preferably collimated prior to hitting the first mirror and/or the at least one second mirror. The collimator preferably comprises a set of Fresnel lenses. The Fresnel lenses are preferably mounted proximal the light source. In arrangements comprising a first mirror and at least one second mirror, the Fresnel lenses are preferably mounted between the light source and the at least one second mirror. In arrangements not including at least one second mirror, the Fresnel lenses are preferably provided between the light source and the first mirror. The light source preferably comprises a plurality of individual light sources, such as light emitting diodes, krypton lamps, tungsten lamps etc. The individual light sources are preferably mounted on a reflective substrate. The individual light sources are preferably arranged in a circle, an ellipse, a rectangle or other geometrical shape. A first aperture is preferably provided in the circle, ellipse, rectangle or other shape defined by the individual light sources. In arrangements comprising a first mirror and at least one second mirror, the first mirror may be located inside the first aperture. The light engine preferably further comprises at least one second mirror for reflecting light from the light source onto the first mirror. The at least one second mirror preferably has a second focal point. The first mirror is preferably located between the at least one second mirror and the second focal point. The or each second mirror is preferably circular in plan form. The light engine preferably comprises a plurality of second mirrors having a common second focal point. The second mirrors may be arranged in a circle, an ellipse, a polygon or any other shape. A second aperture is preferably formed by the second mirrors. The second mirrors may be formed separately and mounted on a frame member in the light engine. Preferably, however, the second mirrors are formed integrally. In one arrangement, the first mirror and the at least one second mirror are hyperbolic mirrors. In another arrangement, the first mirror is a spherical mirror and the at least one second mirror is an elliptical mirror. In a further arrangement, the first mirror is an elliptical mirror and the at least one second mirror is a parabolic mirror. It will be appreciated that the first mirror may be a hyperbolic, elliptical or spherical mirror; and the at least one second mirror may be a hyperbolic, elliptical or parabolic mirror. The polarizer is preferably a reflecting polarizer. The polarizer may comprise a polarizing beamsplitting cube. The polarizer preferably also comprises a mirror combined with one or more quarter wave plates to achieve polarization conversion. Alternatively, the polarizer may comprise a mirror combined with one or more half wave plates to achieve polarization conversion. The polarizer may be a polarization converting film. In this arrangement, the polarization converting film is preferably located in front of the light source. In arrangements comprising a first mirror and a plurality of second mirrors, the polarization converting film is preferably located in the second aperture defined by the second mirrors. Alternatively, the polarizer may be located inside a tube. The inside of the tube is preferably reflective. The inside of the tube is preferably coated with a polarization converting film. The tube is preferably shaped to match the shape of the image forming part of a projector. Viewed from a further aspect, the present invention relates to a projector device containing a light engine as described herein. The projector device preferably weighs less than 500 grams. The projector device preferably has a volume no larger than 256 cubic centimetres. The projector device preferably further comprises an image-forming component. The image-forming component of the projector preferably comprises a transmissive liquid crystal microdisplay; a reflective liquid crystal microdisplay; or a digital micro-mirror device. Viewed from a further aspect, the present application relates to a light engine for the delivery and reformatting of the output of a light source, the light engine comprising: a) a light source; b) a first mirror having a first focal point, an aperture being provided in said first mirror; c) a second mirror located between the first mirror and the first focal point, the second mirror having a second focal point; and d) a polarizer located between the second mirror and the second focal point. Viewed from a further aspect, the present invention relates to a light engine for the delivery and reformatting of the output of a light source, the light engine comprising: a. a light source; b. a set of first mirrors with a common first focal point; c. a second mirror located between the set of first mirrors and their common first focal point, the second mirror having a second focal point; and d. a polarizer located between the second mirror and the second focal point. Viewed from a still further aspect, the present application relates to a light engine for the efficient delivery and reformatting of the output of a light source comprising: a. a light source containing an aperture; b. a first set of mirrors with a common focal point that lies within or behind the area of the aperture of the light source, said set of mirrors containing an aperture; c. a second mirror that is located between the set of first mirrors and their common focal point, having a focal point that lies outside the aperture; and d. a polarizer that is located between aperture and the focal point. Viewed from a yet further aspect, the present invention relates to a highly efficient light engine where the light guide function is performed by two simple mirrors that direct the light from a source S onto a target T. In order to increase uniformity and overall efficiency other components such as an integrating rod can be used within the system. In terms of polarization efficiency, the use of additional components which aid in the polarization recovery are employed within the system to increase the overall system efficiency. The invention reduces or minimises the number of optical components required in the overall system and therefore reduces the overall optical losses incurred due to the respective losses incurred at each optical component. Additionally, the present invention allows for shrinkage of the light engine without compromising the collection efficiency of the system that could not be achieved with standard light engines currently known in the art. The simplicity of the proposed light engine allows for a simple reformatting of the light from the source or sources S that is not directly usable by the target T without the need for multiple additional optical components. Consequently, the physical dimensions of the proposed light engine can be reduced whilst the amount of usable light that is delivered to the target is increased. This invention, at least in preferred embodiments, relates to a novel, compact and very efficient design of a light engine for use in digital projection systems. In preferred embodiments, the light engine design uses a mirror configuration to combine the light from a plurality of given light sources into a highly intense narrow light beam and direct it onto the target T which in projector application is the image forming component of the projector. The use of mirrors to direct the light onto the image forming component allows for the first time any light that is not directly usable by the target (light with the wrong polarization state) to be recycled easily by using a reflective polarizer, polarizing beamsplitter or the like. In a first preferred embodiment the source for the light engine is an array of preferably white light emitting diodes (LEDs) which are positioned in a circular fashion as shown in Figure 1. Each LED faces in the same forward direction and each LED is preferably positioned substantially parallel or exactly parallel to the other LEDs in the array. Referring to Figure 3, the light from each of the LEDs is typically emitted at a full field angle of anywhere between 15 and 120 degrees, and is preferably collimated before striking the first mirror. This may be achieved by placing either a reflector, a lens or a combination of both in front of each LED, such that the focal length of the lens is of the correct value to collimate the incoming light beam. The lenses in question can be, but are not limited to, moulded Fresnel lenses and the reflector can be, for example, of a parabolic shape. The array of reflectors or lenses is preferably constructed in one piece as shown in Figure 2, which simplifies manufacture and assembly of components. The collimated beam then strikes a first mirror, which can be a concave paraboloid, but is not restricted to this shape. This first mirror preferably has a single focal point, at which all incident collimated light rays will meet. A second mirror, which can be a convex hyperboloid, but is not restricted to this shape, is placed between the first mirror and its focal point. This second mirror also has a focal point to which the light rays are now directed. The first mirror is preferably circular concave and the second mirror is preferably convex. This arrangement advantageously directs the light from each of the LEDs towards a common focal point. This means that a high intensity light beam with a very narrow diameter can be formed from the combination of extended sources, which are placed in a much larger array. The high intensity narrow light beam is passed through a polarizer, which is preferably located at the aperture of the first mirror, where the light rays exit the light engine system. The light rays can be used to illuminate a target T, for example a microdisplay or the like, which can in turn be projected onto a suitable screen using projection optics. In another embodiment a reflecting polarizer, such as the type supplied by 3M under the product name "Dual Brightness Enhancement Film", is placed at the aperture of the first mirror instead of a standard absorbing polarizer as shown in figure 4. In this case only the light rays of one polarization is transmitted through the polarizer, whereas the other polarized component of the light beam, which has the opposite polarization, is reflected back into the light engine system. Said component can have its polarization direction reversed and reflected back from the system towards the polarizer, essentially recycling the polarization, which would normally be absorbed or 'lost' in a conventional system. The fact that the initial reflected light from the polarizer is depolarized by multiple reflections, allows it to be recycled, and therefore increases the transmission of usable light through the polarizer to the target T by a factor of around 1.8. In another embodiment of the invention the reflective polarizer is placed within a reflective tube at the aperture of the first mirror as shown in figure 5. The width and the length of this reflective tube are optimised as to maximise the recovery of the light that is initially reflected back from the reflective polarizer. In an additional embodiment of the invention the inside of the reflective tube is coated with a thin layer of scattering material that aids depolarization of the initially reflective light from the reflective polarizer in order to maximise the overall amount of usable light that reaches the target T. In another embodiment of the invention the polarizing component is a polarizing beamsplitter cube (PBS). The unpolarized light incident on the PBS is split into two polarized components, S and P. The P component passes directly through the PBS and onto the image forming component, whereas the S component is reflected at an angle of 90 degrees from the P component. A quarter wave plate is placed in the light beam which converts the linear S polarization state to a circular polarized state. The circularly polarized beam is reflected off a third mirror which reverses the polarization state to the opposite direction (RH to LH or vice-versa), and then directs it towards an aperture in mirror. Another quarter wave plate is located between the third mirror and aperture, which converts the polarization state back to linear, but now in the opposite direction to which it started. The beam reflects off the second mirror and back into the PBS where it passes straight through as it is now in the P polarized state. In another embodiment of the invention an integrating rod is placed between the second mirror and the polarizing component in order to create a more uniformly intense light beam. Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying Figures, in which: Figure 1 shows the circular array of individual light sources according to a first embodiment of the present invention; Figure 2 shows the circular array of Fresnel lenses according to the first embodiment of the present invention; Figure 3 shows schematically a sectional view of the assembled light engine according to the first embodiment of the present invention, comprising an array of light sources, a lens array, a set of first mirrors, a second mirror and a reflecting polarizing component; Figure 4 shows schematically a sectional view of an assembled light engine according to a second embodiment of the present invention, comprising an array of light sources, a lens array, a set of first mirrors, a second mirror, a reflecting polarizing component and a reflective tube; Figure 5 shows schematically a sectional view of an assembled light engine according to a third embodiment of the present invention, comprising an array of light sources, a lens array, a set of first mirrors, a second mirror, a polarizing beamsplitter, two quarter wave plates and a third mirror; and Figure 6 shows schematically a sectional view of an assembled light engine according to a fourth embodiment of the present invention. Figure 1 shows by means of example the configuration of a light source 100 according to the present invention. The light source 100 comprises a plurality of individual light sources 101 which are arranged in such a geometrical fashion as to define a first aperture 102. The individual light sources 101 are in this example arranged in a circular fashion but any other geometrical configuration is also conceivable. The first aperture 102 is circular in the present embodiment, but may be elliptical, rectangular or polygonal. The individual light sources 101 are mounted onto a substrate 103. The surface of said substrate 103 that faces the set of first mirrors 200 is preferably reflective. Figure 2 shows by means of example the configuration of a lens system 105 that is used to collimate the light that is emitted from the individual light sources 101. Said lens configuration consists of a set of individual Fresnel lenses 110 that are mounted onto a substrate 112. The lenses 110 form a second aperture 111 which corresponds generally to the first aperture 102. The spacing of the individual Fresnel lenses 110 should be chosen in such a way that at least each one of the individual Fresnel lenses collimates the light emitted from at least one of the individual light sources 101. Figure 3 shows by means of example the configuration of a proposed light engine 1 according to the invention. The individual light sources 101 as previously shown in figure 1 emit light that is collimated by the lens system 105 shown in figure 2. The collimated light beam now hits a set of first mirrors 200. The first mirrors 200 have a common first focal point 207. Said first mirrors 200 are arranged in such a way as to create a third aperture 206. The collimated light is subsequently reflected off said first mirrors 200 toward a second mirror 203, which is located between the first mirrors 200 and their common first focal point 207. Ideally, said second mirror 203 should be located close to the first aperture 102 of the light source 100. Said second mirror 203 has a second focal point 208. The second mirror 203 directs the collimated light reflected from the first mirrors 200 toward its focal point 208 therefore creating a high density, small, uniform light beam from a significantly larger array of light sources. The high intensity, small light beam that is reflected off the second mirror 203 is preferably passed through a reflective polarizer 204, which is located between the second focal point 208 of the second mirror 203 and the second mirror 203 itself. The polarizer 204 should preferably be located within the third aperture 206, created by the first mirrors 200. The light with the correct polarization is transmitted through the polarizer 204 toward a target T. The light with the wrong polarization is reflected back into the light engine and can be recycled as the polarization of said reflected light will change due to the multiple reflections while going again through the light engine 1. A second embodiment of the light engine 1 is shown in Figure 4. The second embodiment is a modified version of the first embodiment described herein and like reference numerals have been used for like components. The light engine 1 according to the second embodiment has been modified slightly as a tube 209, which is reflective at the inside, has been placed within the third aperture 206 created by the first mirrors 200. The polarizer 204 is located either within the tube 209 or at the end of the tube 209. The reflective tube 209 redirects the light that is reflected off the polarizer 204 onto the centre of the second mirror 203. This is considered to be beneficial according to the present invention as it increases the amount of light that can be recycled as the reflected light from the polarizer does not have to travel through the entire light engine as shown in figure 3 but only travels between the second mirror 203 and the polarizer 204. A light engine 300 according to a third embodiment of the present invention is shown in Figure 5. The third embodiment has a more detailed configuration and includes an integrating rod 309 and a polarizing beamsplitter 305. An array of individual light sources 302 are contained within reflectors 301. The individual light sources emit light that is collimated by a lens system 302 that is configured in the same way as the lens system 105 shown in figure 2. The collimated light beam hits a set of first mirrors 304 having a common first focal point. The first mirrors 304 are arranged to create a first aperture. The collimated light is subsequently reflected off said first mirrors 304 toward a second mirror 303, which is located between the first mirrors 304 and their common first focal point. The second mirror 303 has a finite focal length and has a second focal point. The second mirror 303 directs the collimated light reflected from the first mirrors 304 toward the second focal point, thereby creating a high density, small, uniform light beam from a significantly larger array of light sources. The high intensity, small light beam that is reflected off the second mirror 303 is passed through a polarizing beamsplitter 305, which is located between the focal point of second mirror 303 and the second mirror 303 itself. The polarizing beamsplitter 305 is preferably located after the integrating rod 309, which integrates the light, reflected by the mirrors 304 and 303. The light with the desired polarization is transmitted through the polarizing beamsplitter 305 toward a target T. The light with the opposite polarization is reflected back into the light engine via two quarter wave plates 306 and 308 and a mirror 307 which can be either plane or curved. The light which is reflected from the beamsplitter 305 passes through a quarter wave plate 306 which converts the plane polarized light to circularly polarized light. This circularly polarized light is reflected by a third mirror 307 back towards the convex second mirror 303, but the handedness of the polarization is changed on reflection from the third mirror 307. The light beam passes through a second quarter wave plate 308 which converts the polarization state back to linear, but in the opposite state to which it left the beamsplitter in. The light beam is reflected again from the second mirror 303 and is directed once again towards the beamsplitter 305 where it now passes through towards a target T. A light engine 400 according to a fourth embodiment of the present invention will now be described with reference to Figure 6. The light engine 400 has a light source 401 comprising an array of LEDs 402 mounted on a reflective substrate 403. An array of Fresnel lens 404 is provided for collimating the light emitted from each of the LEDs. Preferably, at least one Fresnel lenses 404 is provided for each LED 402. The LEDs 402 are arranged in a ring and directed towards a first convex mirror 405. The first mirror 405 has a finite focal length and a first focal point. A polarizing beamsplitter 406 is provided between the first mirror 405 and the first focal point. The beamsplitter 406 allows light having the desired polarization to pass through towards a target T but reflects light with the opposite polarization towards a second mirror 407. The second mirror 407 is arranged to reflect light back towards the first mirror 405. A first quarter wave plate 408 is provided between the beamsplitter 406 and the second mirror 407 and a second quarter wave plate 409 is provided between the second mirror 407 and the first mirror 405. The operation of the light engine 400 according to the fourth embodiment of the present invention will now be described. Light is generated by the LEDs 402 and collimated by the Fresnel lenses 404. The collimated light is reflected by the first mirror 405 through the beamsplitter 406. The beamsplitter 406 allows light of the desired polarization to continue towards the target T. The light with the opposite polarization is reflected towards the second mirror 407 and passes through the first quarter wave plate 408 which converts the plane polarized light to circularly polarized light. The first quarter wave plate 408 converts plane polarized light reflected form the beamsplitter 406 to circularly polarized light. The circularly polarized light is reflected by the second mirror 407 back towards the first mirror 405, but the handedness of the polarization is changed on reflection from the second mirror 407. The light beam passes through the second quarter wave plate 409 which converts the polarization state back to linear, but in the opposite state to which it left the beamsplitter. The light beam is reflected again from the second mirror 303 and is directed once again towards the beamsplitter 305 where it now passes through towards the target T. The fourth embodiment of the present invention is particularly advantageous since it further reduces the number of components within the light engine 400. The efficiency of the light engine 400 may thereby be improved. It will be appreciated that various changes and modifications can be made to the light engine described herein without departing from the scope of the present invention. For example, the set of first mirrors and/or the second mirror in the first, second and third embodiments may be moveable to allow the output of the light engine to be adjusted. Equally, in the fourth embodiment the first mirror may be moveable. The position and/or orientation of the light source may also be adjustable. It will be appreciated that the light engine is usually provided in a housing, for example of a projector system, for protection.