Patent ID: 7461954

Claim:
An illumination system, comprising: an arc tube including a light-emitting portion that emits light between electrodes and sealing portions arranged on both sides of the light-emitting portion; a first reflecting mirror that is arranged on a rear side of the light-emitting portion along a longitudinal direction of the arc tube; and a second reflecting mirror that is arranged on a front side of the light-emitting portion, a diameter D 1 on an opening end of a reflecting surface of the first reflecting mirror, indicated by an available marginal light emitted to the rear side from the light-emitting portion, being larger than a diameter d 1 of the outer surface of the second reflecting mirror, the diameter d 1 of an outer surface of the second reflecting mirror being set to a size within the light of an available marginal light reflected by the first reflecting mirror, and the available marginal light being an inside boundary light of a range to be actually used as illuminating light; the second reflecting mirror being arranged so that the light emitted from a center of the light-emitting portion and incident on the second reflecting mirror and a normal of the second reflecting mirror agree with each other, a boundary light L 8 being between light emitted from an end of an arc generated between the electrodes adjacent to the first reflecting mirror that is intercepted by the second reflecting mirror and light emitted from the end of the arc generated between the electrodes adjacent to the first reflecting mirror that is not intercepted by the second reflecting mirror, a diameter D 2 ′ of an opening end of the reflecting surface of the first reflecting mirror having a size such that the first reflecting mirror reflects the boundary light L 8 of the light emitted from the end of the arc generating between the electrodes adjacent to the first reflecting mirror, the end of the arc overlaps with the end of the electrodes.