In this video, we’ll look at a Light Dependent Resistor and see how it works. Let’s get started.

Hi, I’m Hus. In this video, we will look at a Light Dependent Resistor, or an LDR, and see how it changes its resistance based on the light intensity and then connect it in a series circuit and see how it affects the circuit parameters.

This is an LDR, or a Light Dependent Resistor. Rather than using this component, we will use the one that we have installed in our DC Pracbox. This is the Light Dependent Resistor that we’ll use for our demonstration today. First, we’ll measure its resistance based on the light intensity and see how it changes.

Right now, I’ve connected the multimeter in ohmmeter setting across the LDR, and we are basically in the ambient lighting, and it’s showing us a resistance of 380 ohms, keeps changing based on the light intensity on it. If we were to cover the LDR and make it darker, you can see how the resistance changes, and if I cover it all together, I get a resistance of about 1.7 kilo ohms.

If I use my phone’s torch, I should be able to change its resistance based on the light. So if I use my torch, you can see how the resistance goes as low as about 84, 85 ohms. That’s because the light intensity is quite bright. So what it looks like is when it’s bright, the resistance goes down, and when it’s dark, the resistance goes up. Let’s now connect the LDR in series with the LED and see how that changes the circuit parameters.

We’ll connect this circuit to see how the LDR works in a circuit. So we’ll have our 12 volt power supply. We’ll have our LDR, and then we’ll have an LED in series. Let’s connect the circuit.

So we’ve connected this, we’ve connected this wire, and we’ve connected this wire. Let’s turn on this circuit and see what the LDR does to the LED brightness. So if I turn that on, I have my LED at a certain brightness. As I cover the LDR, you can see that the LED’s brightness changes. It’s gone a bit dimmer, and as I let it go, it gets a little bit brighter. So when I cover it, it’s dim, let it go, it’s bright.

Now, we want to see what’s happening to the circuit parameters, so I’m going to introduce our ammeter into the mix of this. To connect the ammeter, I will turn off the supply. I will set my meter at milliamps range because I know it’s an LED, it’s not going to draw a lot of current, and I will take my power cable, send it to the multimeter from the multimeter back to the LDR. So now, my circuit is power supply, ammeter, LDR, LED, and back to my power supply. Let’s turn it on and see what current we get in ambient lighting.

So right now, we’re getting about 9.9 milliamps, so about 10 milliamps. As I cover the LDR, you can see how that current changes, and if I cover it completely, my current goes down to about five milliamps as opposed to 9, and that’s why my LEDs dim. If I remove the cover and back into ambient lighting, it’s back to about 10 milliamps. Let’s use our torch and see what that does to the current.

As I shine the torch close to the LDR, you can see that the current is changing, and when I bring it as close as I can, the current goes all the way to about 13 milliamps, and that’s why the LED is brighter. Let’s now measure voltage across the LDR and then the LED and see how the voltage drop changes based on the light intensity.

For this circuit, I will remove my ammeter from the circuit, and then connect the voltmeter across the LDR, and then connect it across the LED and take some measurements. Now that I have my circuit ready, let’s power it up and see what the voltage is across the LDR in ambient lighting.

So in ambient lighting, I have about 3.5 volts across the LDR, and since my power supply is 12, the rest of it is across the LED. As I cover the LDR, the resistance of the LDR increases, which means the voltage drop across increases as well. At the same time, the voltage drop across the LED should also change, which is now making the LED dimmer. Let’s now check the voltage across the LED.

In ambient lighting, I have about 8 volts across the LED. If you remember, LDR was showing about 3.5 volts, so that’s adding up to about 12, and if I cover the LDR, the voltage across the LDR goes up, which means the voltage across the LED goes down, and now, I have only about five volts across it. So if I increase the light intensity on the LDR, you can see how the voltage across the LED also increases because the resistance of the LDR is decreased.

As you saw in the demonstration, Light Dependent Resistor or an LDR changes its resistance based on the light intensity. So when it was dark, the resistance went up, and when it was bright, the resistance went down. We then connected in series with the LED, and that started affecting the LED brightness. So when it was darker, the resistance of the LDR was higher, so there was less current in the circuit, which made the LED dimmer, and when it was brighter, the resistance was down, more current in the circuit, which made the LED brighter.

I hope you enjoyed the video. If you have any questions or feedback, please feel free to contact us. Thanks for watching.