Introduction

An Automatic Night Lamp using LDR (Light Dependent Resistor) is a simple and useful electronics project that automatically turns ON a light when it becomes dark and turns it OFF when there is sufficient light. This project is widely used in homes, streets, gardens, and pathways to save electricity and improve convenience.

This project is ideal for beginners because it introduces basic sensors, transistor switching, and automatic control systems.

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Objective of the Project

The main objective of this project is:

• To automatically control a lamp based on ambient light conditions.
• To reduce manual effort and save electrical energy.
• To understand the working of an LDR and transistor-based switching circuit.

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Working Principle

The working of the automatic night lamp is based on the resistance property of the LDR.

• In daylight:
  The LDR has low resistance, so the transistor does not get enough base voltage. As a result, the LED or bulb remains OFF.
• In darkness (night):
  The LDR resistance becomes high, which increases the voltage at the transistor base. This turns the transistor ON, allowing current to flow and switching the LED/bulb ON automatically.

Thus, the lamp turns ON at night and OFF during the day without any manual switch.

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Components Required

• LDR (Light Dependent Resistor)
• Transistor (BC547 or equivalent)
• LED / Bulb
• Resistor (10kΩ, 220Ω)
• Potentiometer (optional – for sensitivity control)
• Power Supply (5V–12V DC)
• Breadboard and connecting wires

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Circuit Diagram

          +Vcc
           |
           |
          [LDR]
           |
           +-------> Base of Transistor (BC547)
           |
         [10kΩ]
           |
          GND

Collector of Transistor ---- LED ---- 220Ω ---- +Vcc
Emitter of Transistor -------------------- GND

Circuit Explanation

• The LDR and resistor form a voltage divider.
• The voltage divider controls the base of the transistor.
• When it is dark, the transistor turns ON and allows current to flow through the LED.
• When it is bright, the transistor turns OFF and the LED remains OFF.

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Advantages

• Fully automatic operation
• Low power consumption
• Simple and low-cost circuit
• Saves electricity
• No manual switching required

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Applications

• Automatic street lights
• Garden and pathway lighting
• Night lamps for homes
• Energy-saving lighting systems
• Smart city lighting project