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Here, a photoresistor acts as the light-sensing element in a simple light meter.

When dark, the photoresistor is very resistive, and little current flows through the series loop; the meter is at its lowest deflection level.When an increasingly bright light source is shone on the photoresistor, the photoresistor’s resistance begins to decrease, and more current begins to flow through the series loop; the meter starts to deflect. The potentiometer is used to calibrate the meter.