Photo Resistor Dark Resistance: Definition and Basics

This page explains the definition of a photo resistor, the basics of photo resistor dark resistance, and the equation used to calculate it.

What is a Photo Resistor?

A photo resistor is a device whose resistance decreases as the amount of light incident upon it increases. It’s also commonly known as an LDR (Light Dependent Resistor) or a photoconductor.

Essentially, when more light shines on its surface, the resistance drops, allowing current to flow more easily through the circuit.

Figure 1: Typical components of a photo resistor.

What is Photo Resistor Dark Resistance?

Dark resistance refers to the resistance of a photo resistor when it’s kept in complete darkness.

When there’s no light present, the resistance is at its highest.