Light quantity setting value determination with improved reliability

摘要

A light quantity sensing device senses when a light quantity emitted by a light emitting device becomes respectively equal to a plurality of different predetermined light quantities, the light quantity sensing device then providing a plurality of sensing signals corresponding to the plurality of different predetermined light quantities. A setting value determination device determines in response to the plurality of light sensing signals provided by the light quantity sensing device a plurality of light quantity setting values corresponding to the different predetermined light quantities, the plurality of light quantity setting values then being used for driving the light emitting device so that the light emitting device emits the plurality of different predetermined light quantities corresponding to the plurality of light sensing signals. An abnormal condition sensing device senses when the light quantity sensing device does not operate correctly, the abnormal condition sensing device then processing a predetermined operation so as to prevent an undesirable condition being caused by the incorrect operation.