LDR: Automatic LED On/Off

In the previous lesson, we learned about the potentiometer, a variable resistor that can be adjusted manually.

Now we will learn about another special type of resistor: the Light Dependent Resistor (LDR).

Unlike a potentiometer, an LDR changes its resistance automatically depending on the amount of light falling on it.

In this lesson, we will learn:

• ☀️ What is an LDR?
• 🌑 How an LDR reacts to darkness
• 💡 How an LDR reacts to light
• ⚡ How its resistance changes
• 🔧 How to measure an LDR using a multimeter
• 💡 How to build an automatic LED ON/OFF circuit using an LDR 

LDR stands for Light Dependent Resistor.

It is a type of resistor whose resistance changes according to the amount of light falling on its surface.

It is also commonly called:

• Photoresistor
• Photocell
• Light sensor

In bright light ☀️

The LDR's resistance becomes lower.

In darkness 🌑

The LDR's resistance becomes higher.

You should see the resistance increase as the amount of light decreases.

This is a simple way to observe the working principle of an LDR.

In this lesson, you learned:

• ☀️ What an LDR is
• 💡 How an LDR responds to light
• ⚡ How its resistance changes
• 🌑 Why its resistance increases in darkness