# Automatic Night Light circuit using LDR and Relay

Hello guys, today I am going to tell you an easy way to make an Automatic night light circuit(automation) without using any micro-controllers or development board. With a circuit diagram as well as a simulation video of working of this project. This is possible with a simple analog circuitry using some active components as well as some passive components working collectively. So let’s get started with Automatic Night Light circuit

So, lets first focus on the materials and components needed:-

#### Materials:

• Transistor TIP122 -1pc
• R1 220K -1pc
• LDR1 -1pc
• 12v relay[SPDT] -1pc
• D1 1N4007
• 12v battery
• Lamp/bulb/socket
• PCB board-1pc
• miscs like multimeter/solder,wires,etc.

Below is the circuit diagram and its working:-

### Automatic Night Light Circuit

The circuit is employing an LDR (light dependent resistor), transistor TIP122, an SPDT RELAY 12V, and a small resistor 220K as components making this circuit working.

Working step by step:-

DAY TIME OR UNDER LIGHT INTENSITY

During the day time or when the light is falling over the LDR, its conductivity increases with a decrease in its resistivity, making the transistor working as the switch is turned off by shorting the base and emitter terminal also connecting the base to the ground and as our relay doesn’t get power to its coil, so no deflection happens within the pins and lamp or light does not glow.

In PROTEUS, I have used a torch to simulate day time and turned it off to simulate LDR under dark.

#### For NIGHT TIME/OR IN ABSENCE OF LIGHT

When in absence of light LDR doesn’t get that much light and its resistance does not decrease. So the base and emitter are not shorted and the base separately gets +ve making the transistor ON and emitter goes to the ground. This turns the relay ON and its pin deflects and connects COM TO NO.or in simple language we can say light is turned on via relay by completing the circuit by connecting it to mains 220-230V AC.

I hope You guys enjoyed this project and have understood the concept clearly. If you guys liked it, please comment below and let me know how you felt about this project.

Aabhishek
Hello, all this is Aabhishek Sharma and I'm an engineer, blogger, and SEO(Search Engine Optimization). I love making cool electronics circuits and gadgets. Currently, also a Computer Science Engineering student.
http://www.electroinvention.co.in

## 8 Replies to “Automatic Night Light circuit using LDR and Relay”

Well it didn’t worked with 220k resistor but worked with 100k resistor

1. It is also dependent on your input Current. I guess the voltage was the same 12v in your case too, but the variation in input current may be a factor too. A person with 12v 1a input and a person with a 12v 2A or 3A input may have different observations.
But yes, a circuit with 100k is better more sensitive to light. I made it to be 220K so it’s still not glowing or blinking when it’s about to be dark or mid-evening, and only glowing the light when it’s dark and turn off when it is absolutely bright.
Thanks for visiting and thanks for giving reviews.