| 摘要 |
In one illustrative embodiment, a method is provided that comprises energizing a light source to provide light having a preselected intensity. A first photosensor, which is capable of delivering a first signal indicative of the intensity of the light source, is exposed to the light source. A second photosensor, which is also capable of delivering a second signal indicative of the intensity of the light source, is also exposed to the light source. Thereafter, the first and second signals are compared, and an error signal is delivered in response to detecting a significant difference between the first and second signals.
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