Smart Night Light

What You'll Build

This project turns your Arduino into something genuinely useful: a lamp that knows when it is dark. A light sensor watches the room, and the moment the brightness drops below a level you choose, the LED fades on. When someone opens the curtains again, it quietly switches off.

What You Need

• ✓Arduino Uno
• ✓LDR (photoresistor)
• ✓10kΩ resistor
• ✓White LED
• ✓220Ω resistor
• ✓Breadboard

How It Works

A photoresistor (LDR) changes its resistance depending on how much light hits it: bright light means low resistance, darkness means high resistance. Paired with a fixed 10kΩ resistor it forms a voltage divider, and the Arduino's analog pin reads that voltage as a number from 0 to 1023. Your code compares that number to a threshold and decides whether the lamp should be on.

Before You Wire It

Wiring

Step-by-Step Instructions

1. 1

   Build the sensor divider

   The LDR and the 10kΩ resistor sit in a line between 5V and GND. The wire that reads the value comes from the point exactly between them — that middle point is what A0 measures.

2. 2

   Add the lamp

   Wire the white LED to pin 9 through its 220Ω resistor. Pin 9 supports PWM, which means later you can fade the light instead of just switching it.

3. 3

   Read the sensor first

   Upload the code and open the Serial Monitor at 9600 baud. Cover the LDR with your hand and watch the number change — that is your sensor talking to you.

4. 4

   Pick your threshold

   Write down the reading in a bright room and the reading with your hand over the sensor. Choose a number halfway between them and put it in the code.

5. 5

   Test in the dark

   Turn the room lights off. Your lamp should glow on smoothly within a second.

Arduino Code

const int LDR_PIN = A0;
const int LAMP = 9;
const int DARK_LEVEL = 400;   // change to suit your room

void setup() {
  pinMode(LAMP, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int light = analogRead(LDR_PIN);
  Serial.println(light);

  if (light < DARK_LEVEL) {
    analogWrite(LAMP, 200);   // soft glow
  } else {
    analogWrite(LAMP, 0);     // off
  }
  delay(200);
}

Understanding the Code

Challenges & Upgrades

Troubleshooting

Helpful Resources