Arduino: Use LED As a Light Sensor




Introduction: Arduino: Use LED As a Light Sensor

A while ago, I read a blog post about using a normal LED as a light sensor. After browsing around the Internet, I found that all the examples that I found were not working well or hard to read. Then I stumbled upon this instructable:

However, I found that the code was kind of hard to read/edit and it missed a serial output. Below is the cleaned up code with serial output. In addition, I found that adding a 100R resistor in series with the sensing LED greatly improves the sensitivity. This change improves the range of light on the serial port from 290-270 to 290-120.

#define READ A0
#define LED 13
int basis = 0;

void setup() {
  pinMode(LED, OUTPUT);

void loop() {
  int sens = readLED(50);
  basis = sens - 20;                 // setting sensitivity - now it will react if the LED is 20 lower than the setting above
  for(int y = 0; y < 1000; y++) {    // after every 1000 tests the program will reset the led to cope with changing light
    sens = readLED(50);
    if (sens < basis)                // testing is the led was in the dark
      digitalWrite(LED, HIGH);     
      digitalWrite(LED, LOW);

int readLED(int number) {            // Read analog value n times and avarage over those n times
  int totaal = 0;
  for(int x = 0; x < number; x++) {
    totaal += analogRead(READ);
  return totaal/number;

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    6 Discussions

    Vibhor 0001
    Vibhor 0001

    1 year ago

    I am amazed
    Can you give me step by step explanation of the code
    Please sir.
    thank you


    4 years ago

    This does not use the LED as a light sensor but rather an antenna. It picks up 50/60Hz noise from the grid. If you put your hand close to the LED without changing the incident light you will see the thing still "working". If you remove the LED and replace it with a small wire it will continue "working".


    7 years ago on Introduction

    I will come with a better Ible soon :) (and better code)
    I didn't have the same result with the resistor tough.


    7 years ago on Introduction

    this works great,
    is there a way to alter the code so the output led is the same as the sensor led?
    I tried this ( code, but doesn't seem to be very stable.