LED as Sensor ?in reverse or forward bias??

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i read post related , got led can generate small photo current when throw light towards it.
i tried lm358(op-amp),i connected in reverse bias , got same result.

but question when connected led anode bc547 base , cathode gnd(as shown in attached file),
i mean in forward bias worked!and able switch led on (not ther "some" light) connected collector?

i mean use led sensor should work in reverse bias?they why worked bc547 in forward bias?please tell me curious know this.. :smiley-mr-green:

the led can make positive current when connected in forward bias. if reversed, provide negative current. forward bias, shown in schematic, correct bias turn on npn transistor using photocurrent.


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