Light-dependent resistors

A light-dependent resistor (LDR) is a resistor whose resistance changes with the intensity of the light falling on it. As light intensity increases, its resistance decreases. As light intensity decreases, its resistance increases.

If the potential difference across the LDR is kept fixed, a decrease in resistance allows a larger current to flow. The LDR therefore provides an electrical response that depends on the light falling on it.

LDR circuit symbol

The circuit symbol for an LDR is a resistor with arrows pointing towards it, commonly enclosed by a circle. The inward-pointing arrows represent light falling on the LDR and distinguish it from a component that emits light.