Patent ID: 7448758

Claim:
An illumination unit comprising: first, second, third, and fourth light source units to emit first, second, third, and fourth light beams of different wavelength bands; and a hexahedral color synthesis prism to synthesize the first, second, third, and fourth light beams emitted from the first, second, third, and fourth light source units to propagate the first, second, third, and fourth light beams along the same path, wherein the color synthesis prism comprises: first and second entrance surfaces opposing each other and allowing the first and second beams to be respectively incident therethrough; a third entrance surface disposed adjacent to the first and second entrance surfaces and allowing the third beam to be incident therethrough; a fourth entrance surface disposed adjacent to the first, second, and third entrance surfaces and allowing the fourth beam to be incident therethrough; an exit surface disposed adjacent to the first, second, and fourth entrance surfaces to oppose the third entrance surface and allowing the first through fourth beams to be emitted therethrough; a first dichroic mirror to reflect the first light beam incident through the first entrance surface toward the exit surface and to transmit the second, third, and fourth beams therethrough; a second dichroic mirror to reflect the second light beam incident through the second entrance surface toward the exit surface and to transmit the first, third, and fourth light beams therethrough; and a third dichroic mirror to reflect the fourth light beam incident through the fourth entrance surface toward the exit surface and to transmit the first, second, and third light beams therethrough.