Automatic night light

An LDR divider senses darkness and switches a lamp on.

Open in Circuit Lab Simulator

Interactive Simulation

Automatic night lightarduino-uno

Open in Lab

Required Components Checklist

Assembly Steps

Build the divider

LDR from 5V to A0, 10 kΩ from A0 to GND.

Find your threshold

Print the readings in normal light and with your hand over the sensor, then pick a value in between.

Switch the lamp

Compare the reading with the threshold and set the LED.

Arduino Sketch

const int LIGHT_PIN = A0;
const int LED_PIN = 9;
const int DARK_BELOW = 400; // tune this: lower = darker before the light turns on

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

void loop() {
  int light = analogRead(LIGHT_PIN); // more light → lower LDR resistance → higher reading
  bool dark = light < DARK_BELOW;
  digitalWrite(LED_PIN, dark ? HIGH : LOW);
  Serial.print("light=");
  Serial.print(light);
  Serial.println(dark ? "  -> lamp ON" : "  -> lamp off");
  delay(300);
}

Challenges & Extensions

Ready to take this project further? Try these challenges:

•Add hysteresis so it doesn't flicker at dusk.
•Fade the LED brighter as it gets darker using analogWrite.
•Keep the lamp on for 10 s after it becomes light again.