LDR Sensor Basics

What is an LDR?

LDR stands for Light Dependent Resistor.It’s a small electronic part that changes how much electricity can pass through it depending on how much light hits it.

How it works

• When it’s bright, it’s like opening a big door — electricity flows easily.

• When it’s dark, it’s like closing the door — electricity can barely get through.

☀️ More light → lower resistance → more current

🌙 Less light → higher resistance → less current

The ceramic base

• The round disc of the LDR is made from ceramic — a hard, heat‑resistant material.

• It acts as the foundation that holds everything together.

• It doesn’t conduct electricity; it just supports and insulates the metal parts on top.

The zig‑zag track

• On top of the ceramic, you’ll see a squiggly or zig‑zag line—that’s the resistive track.

• It’s made of a special light‑sensitive material called cadmium sulfide (CdS).

  
  

That zig‑zag shape just makes the track longer, so the sensor’s resistance covers a wider range.

Where you see them

• Streetlights that turn on automatically at night

• Solar garden lights

• Robots that follow light

• Phone screens that dim in the dark