ESP32 - Light Sensor

This tutorial instructs you how to use ESP32 with the light sensor. In detail, we will learn:

Hardware Used In This Tutorial

1×ESP-WROOM-32 Dev Module
1×Micro USB Cable
1×Light Sensor
1×10 kΩ resistor
n×Jumper Wires
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Introduction to Light Sensor

The most wide-used light sensor is a photoresistor (also known as photocell, or light-dependent resistor, LDR).

It can be used to detect the presence ofthe light. It can also be used to measure the illuminance/brightness level of the light.

Light Sensor Pinout

A light sensor has two pins. Just like a normal resistor, We do NOT need to distinguish these pins.

Light Sensor Pinout

How Light Sensor Works

The photoresistor's resistance is in inverse proportion to the intensity of the light. The less light the photoresistor's face is exposed, the more the photoresistor's resistance is. Therefore, we can infer how bright the ambient light is by measuring the photoresistor's resistance.

wiring diagram between how light sensor works


The value measured by photoresistor reflects the approximated tendency of the light's intensity, it does NOT represent exactly the luminous flux. Therefore, the photoresistor should not be used in an application that requires high accuracy. calibration is also required for some kind application.

ESP32 - Light Sensor

The ESP32's analog input pin converts the voltage (between 0v and ADC_VREF - default is 3.3V) into integer values (between 0 and 4095), called analog value or ADC value. By connecting an analog input pin of ESP32 to the photoresistor, we can read the analog value by using analogRead() function.

Wiring Diagram between Light Sensor and ESP32

wiring diagram between esp32 light sensor

This image is created using Fritzing. Click to enlarge image

ESP32 Code

The below ESP32 code reads the value from a light sensor and infers the light level

/* * This ESP32 code is created by * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit */ #define LIGHT_SENSOR_PIN 36 // ESP32 pin GIOP36 (ADC0) void setup() { // initialize serial communication at 9600 bits per second: Serial.begin(9600); } void loop() { // reads the input on analog pin (value between 0 and 4095) int analogValue = analogRead(LIGHT_SENSOR_PIN); Serial.print("Analog Value = "); Serial.print(analogValue); // the raw analog reading // We'll have a few threshholds, qualitatively determined if (analogValue < 40) { Serial.println(" => Dark"); } else if (analogValue < 800) { Serial.println(" => Dim"); } else if (analogValue < 2000) { Serial.println(" => Light"); } else if (analogValue < 3200) { Serial.println(" => Bright"); } else { Serial.println(" => Very bright"); } delay(500); }

Quick Instructions

  • If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
  • Copy the above code and paste it to Arduino IDE.
  • Compile and upload code to ESP32 board by clicking Upload button on Arduino IDE
  • Open Serial Monitor on Arduino IDE
  • How to open serial monitor on Arduino IDE
  • Radiates light to sensor
  • See the result on Serial Monitor. It looks like the below::
  • COM6
    Analog Value = 406 => Dim Analog Value = 412 => Dim Analog Value = 465 => Dim Analog Value = 471 => Dim Analog Value = 3511 => Very bright Analog Value = 3521 => Very bright Analog Value = 3618 => Very bright
    Autoscroll Show timestamp
    Clear output
    9600 baud  

Light Sensor and LED

Wiring Diagram

wiring diagram between esp32 light sensor led

This image is created using Fritzing. Click to enlarge image

ESP32 Code

The below code turns ON the LED if it is dark, otherwise turns OFF the LED

/* * This ESP32 code is created by * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit */ // The below are constants, which cannot be changed #define LIGHT_SENSOR_PIN 36 // ESP32 pin GIOP36 (ADC0) connected to light sensor #define LED_PIN 22 // ESP32 pin GIOP22 connected to LED #define ANALOG_THRESHOLD 500 void setup() { pinMode(LED_PIN, OUTPUT); // set ESP32 pin to output mode } void loop() { int analogValue = analogRead(LIGHT_SENSOR_PIN); // read the value on analog pin if (analogValue < ANALOG_THRESHOLD) digitalWrite(LED_PIN, HIGH); // turn on LED else digitalWrite(LED_PIN, LOW); // turn off LED }

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