Smart Automatic Room Light using LDR & IR

Problem statement

Lights in classrooms and hostels are often left ON even when there is enough daylight or when nobody is inside, wasting electricity.

Abstract

This project builds a simple automatic lighting system for a room. An LDR senses ambient light level, while an IR or PIR sensor detects human presence. A small controller or comparator circuit decides whether to switch the room light ON or OFF through a relay. The system ensures that the light is ON only when the room is occupied and dark.

Components required

• LDR (Light Dependent Resistor)
• IR or PIR motion sensor
• Op-amp / small microcontroller (optional)
• Relay module
• AC bulb and holder
• Resistors, potentiometer and PCB
• 5V power supply

Block diagram

Working

The LDR forms a voltage divider whose output changes with ambient light. The IR/PIR sensor generates a HIGH signal when a person is detected. The controller or comparator logic checks both inputs: if light level is below a set threshold and presence is detected, the relay is energized and the room light turns ON. When the room is vacant or daylight is sufficient, the relay is turned OFF.

Applications

• Automatic lighting in classrooms and labs
• Hostel corridors and bathrooms
• Energy-saving systems for offices
• Introductory automation project for 1st year