| 摘要 |
PROBLEM TO BE SOLVED: To distinctly display a bearing within observation field by providing an on/off switch turning on/off the power source circuit of an illuminating light source illuminating a bearing panel, a photosensor detecting ambient brightness and an automatic lighting circuit automatically turning on or turning off the illuminating light source according to a signal from the photosensor. SOLUTION: The power source circuit 22 lighting the illuminating light source is turned on by the on/off switch 21, but the illuminating light source is not lit unless another condition is satisfied. In order to light the illuminating light source, the signal from the photosensor 23 must be in a specified range in a state where the circuit 22 is turned on. The specified range means that the output signal from the photosensor 23 is equal to or under a fixed value. The level of the output signal from the sensor 23 is changed in proportion to the ambient brightness. Therefore, when it is dim or darker on the periphery, the level of the output signal gets in the specified range, the automatic lighting switch of the automatic lighting circuit 24 is turned on and the illuminating light source is lit.
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