| 摘要 |
An illumination optical system includes first and second lamp units, a light combining portion that combines a light beam from the first lamp unit and a light beam from the second lamp unit, at least one light returning portion disposed between the first lamp unit and the light combining portion, or between the second lamp unit and the light combining portion, or both, the or each of the at least one light returning portion dividing a part of light emitted from the corresponding lamp unit into a light beam to be returned to the lamp and a light beam to be led to the light combining portion, and a condenser lens that condenses light from the light combining portion.
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