| 摘要 |
PROBLEM TO BE SOLVED: To prolong the life of an optical system without changing a power source to be used. SOLUTION: Every time a power source circuit 5 of a liquid crystal projector 10 is turned on, a microcomputer 6 increases a counter value of a counter 7 by one, stores the value in a memory 8 and checks whether the counter value of this time is an odd number or not. If the value is an odd number, the microcomputer issues an instruction to select the power source A to instruct the lighting of a lamp 11A. When the power source is turned on again after the power source is turned off by a user, the counter value changes and turns to an even number and, therefore, the microcomputer issue an instruction to select another power source B to light another lamp which is not the previously lighted one.
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