9.3.7—The resistance of a light-dependent resistor (LDR) decreases

A light-dependent resistor’s resistance decreases as light intensity increases, because illumination creates more mobile charge carriers in its semiconductor material.

Use it as a variable sensor: the circuit output depends on how the LDR is arranged with other resistors and the supply.

In a potential divider, brighter light lowers the LDR resistance and changes the share of supply voltage across the other component.

An LDR responds to light intensity, not simply to elapsed time or temperature; the direction of voltage change depends on circuit placement.