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LDR

Light Dependent Resistor

Output \(\in [0, 1023]\) $$ \begin{aligned} R &\propto \dfrac{1}{L_V} \ \implies I &\propto L_V \end{aligned} $$ where

  • \(R =\) Resistance
  • \(L_V =\) Intensity of incident light
  • \(I =\) Current

Applications

  • Smart street lights
  • Auto-brightness on Phone

No polarity, as resistors don’t have any polarity

Connection

ldr_wiring_diagram

ldr_wiring_diagram_arduino

Code

int reading;

void setup(){
  pinMode(A0, INPUT); // LDR
  pinMode(D2, OUTPUT); // LED


  Serial.begin(9600);
}
void loop(){
  reading = analogRead(A0);

  Serial.println(reading);

  // if incident light too low -> environment too dark
  // then turn on output light
  if (reading < 50){
    digitalWrite(D2, HIGH);
  }
  else {
    digitalWrite(D2, LOW);
  }

  delay(500);
}
2025-12-01

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