技术功效语段：
In an embodiment of the illumination system, the first part of the discharge vessel forms a further refractive element for reducing a size of an image of the discharge arc, the image being produced by light refracted by the first part and reflected from the back reflector. The high-pressure discharge lamp emits the light from the discharge arc. The discharge arc is not a point source but has a specific dimension. Possibly together with further optical elements, the back reflector generates an image of the discharge arc. In the known illumination systems, the image produced by light emitted from the discharge arc via the first part of the discharge vessel may be relatively large and may be larger than a diaphragm of an optical system which uses the light of the illumination system. Due to this relatively large image, part of the light transmitted by the first part may be lost, thereby reducing the efficiency and brightness of the known illumination system. In the illumination system according to the invention, the shape of the first part of the discharge vessel is adapted to generate a further refractive element. The shape of this further refractive element at the first part is chosen to be such that the size of the image of the discharge arc is reduced. The efficiency of the illumination system is increased by the reduction of magnification of the image produced by light refracted by the first part. The first part of the discharge vessel may have such a shape that substantially all light refracted by the first part and reflected from the back reflector is transmitted through the diaphragm of the optical system, thus substantially avoiding loss of light.
In an embodiment of the illumination system, the spherical aberrations comprise first-order aberrations and/or second-order aberrations and/or third-order aberrations. The spherical aberrations required to further improve the efficiency of the illumination system according to the invention may be any combination of first-order, second-order and third-order aberrations. The spherical aberrations which may be chosen to obtain an optimal shape of the back reflector of the illumination system may be determined by using optical modeling software, such as ASAP®, lighttools®, etc. In an embodiment of the illumination system, the discharge vessel comprises a wall having an outer surface and an inner surface, a shape of the outer surface of the second part being substantially identical to the shape of the outer surface of the first part, and a shape of the inner surface of the second part being different from the shape of the inner surface of the first part, thereby forming the refractive element in the second part. This embodiment has the advantage that it is relatively easy to produce. Generally, the discharge vessel is constituted by two halves each having substantially cylindrical inner walls. By pushing the two halves together at a high temperature so as to obtain the discharge vessel, the inner wall is pushed out to form an inner curved wall. By simply altering the pressure at which the two halves are pressed together during the production process, the curvature of the inner wall may thus be adapted and controlled.
In an embodiment of the illumination system, the inner diameter of the second part at a range of distances from the focal point is at least 10% larger than the inner diameter of the first part at matching distances in a matching range of distances from the focal point on the opposite side of the focal point. An asymmetry of at least 10% results in a measurable improvement of the efficiency and typically exceeds the production process window of contemporary production processes.
权利要求：
CLAIMS:
1. An illumination system (100) comprising a high-pressure discharge lamp (80, 82, 84, 86) at least partially surrounded by a back reflector (30) which is capable of reflecting light emitted by the high-pressure discharge lamp (80, 82, 84, 86) towards a light exit window (50) of the illumination system (100), - the back reflector (30) having an optical axis (55), the high-pressure discharge lamp (80, 82, 84, 86) comprising a discharge vessel (90, 92, 94, 96) enclosing a discharge space and comprising two electrodes (98, 99) between which, during operation, a discharge arc is produced, the discharge arc being located substantially at a focal point (40) of the back reflector (30) on the optical axis (55), - the discharge vessel (90, 92, 94, 96) comprising a first part (10, 14) arranged at least partially between the discharge arc and the back reflector (30), and a second part (20, 22, 24) arranged at least partially between the discharge arc and the light exit window (50), the second part (20, 22, 24) having a different shape compared to the first part (10, 14), thereby forming a refractive element in the second part (20, 22, 24) for reducing an angular distribution at the light exit window (50) of the light emitted from the discharge arc and refracted by the second part (20, 22, 24).
2. An illumination system (100) as claimed in claim 1, wherein the first part (10, 14) of the discharge vessel (90, 92, 94, 96) forms a further refractive element for reducing a size of an image of the discharge arc, the image being produced by light refracted by the first part (10, 14) and reflected from the back reflector (30).
3. An illumination system (100) as claimed in claim 1 or 2, with the back reflector (30) being an ellipsoidal back reflector (30) having the focal point (40) and a further focal point (45), wherein the ellipsoidal back reflector (30) comprises spherical aberrations for redirecting the light transmitted by the second part (20, 22, 24) and/or the first part (10, 14) towards the further focal point (45).
4. An illumination system (100) as claimed in claim 3, wherein the spherical aberrations comprise first-order aberrations and/or second-order aberrations and/or third- order aberrations.
5. An illumination system (100) as claimed in claim 1, 2, 3 or 4, wherein the discharge vessel (90, 92, 94, 96) comprises a wall having an outer surface (60, 62) and an inner surface (70, 72, 74, 76, 78), a shape of the outer surface (62) of the second part (20, 22, 24) being substantially identical to the shape of the outer surface (60) of the first part (10, 14), and a shape of the inner surface (72, 74, 78) of the second part (20, 22, 24) being different from the shape of the inner surface (70, 76) of the first part (10, 14), thereby forming the refractive element in the second part (20, 22, 24).
6. An illumination system (100) as claimed in claim 5, wherein an inner diameter
(d20) of the second part (20, 22, 24) at a distance (x) from the focal point (40) is at least 10% larger than an inner diameter (dio) of the first part (10, 14) at the same distance (-x) from the focal point (40) on an opposite side of the focal point (40), the inner diameter (d10, d2o) of the first part (10, 14) and the second part (20, 22, 24) being defined in a direction substantially perpendicular to the optical axis (55).
7. An illumination system (100) as claimed in claim 6, wherein the inner diameter (d2o - d22) of the second part (20, 22, 24) at a range (Δx) of distances from the focal point (40) is at least 10% larger than the inner diameter (d10 - di2) of the first part (10, 14) at matching distances in a matching range (-Δx) of distances from the focal point (40) on the opposite side of the focal point (40).
8. An illumination system (100) as claimed in any one of the preceding claims, wherein the inner wall (70, 76) of the first part (10, 12, 14, 16) and/or the inner wall (72, 74, 78) of the second part (20, 22, 24, 26) of the discharge vessel (90, 92, 94, 96) in a cross- sectional view along a plane comprising the optical axis (55) is convexly shaped towards the discharge arc, or is concavely shaped towards the discharge arc, or is linearly shaped.
9. A high-pressure discharge lamp (80, 82, 84, 86) for use in the illumination system (100) as claimed in any one of the preceding claims, the illumination system (100) comprising a back reflector (30) having an optical axis (55), the high-pressure discharge lamp (80, 82, 84, 86) comprising a discharge vessel (90, 92, 94, 96) enclosing a discharge space and comprising two electrodes (98, 99) between which, during operation, a discharge arc is produced, the discharge arc being located substantially at a focal point (40) of the back reflector (30) on the optical axis (55), - the discharge vessel (90, 92, 94, 96) comprising a first part (10, 14) arranged at least partially between the discharge arc and the back reflector (30), and a second part (20, 22, 24) arranged at least partially between the discharge arc and the light exit window (50), the second part (20, 22, 24) having a different shape compared to the first part (10, 14), thereby forming a refractive element in the second part (20, 22, 24) for reducing an angular distribution at the light exit window (50) of the light emitted from the discharge arc and refracted by the second part (20, 22, 24).
10. An image projection system (110) comprising the illumination system (100) as claimed in claims 1 to 8.