Patent ID: 8434877

Claim:
An illumination optical system that illuminates an image modulation element, the illumination optical system comprising: a beam combining portion that combines a beam emitted from a first lamp unit and a beam emitted from a second lamp unit, the first and second lamp units each including a lamp and a concave mirror, each lamp having a cathode and an anode arranged along an optical axis of the concave mirror; a lens array or a rod integrator through which a beam from the beam combining portion is transmitted; and a condensing lens that condenses the beam transmitted through lens array or the rod integrator, the beam combining portion including: a first reflective section disposed on an optical axis of the first lamp unit and off an optical axis of the second lamp unit; and a second reflective section disposed off the optical axis of the first lamp unit, wherein the first reflective section and the second reflective section reflect the beam emitted from the second lamp unit and being off the optical axis thereof to combine the beams emitted from the first and second lamp units, and wherein the optical axis of the first lamp unit is substantially perpendicular to the optical axis of the second lamp unit.