Arduino Nano ESP32 - Light Sensor

This tutorial provides instructions on how to use Arduino Nano ESP32 with the light sensor. In detail, we will learn:

How light sensor works.
How to connect light sensor to Arduino Nano ESP32.
How to program for Arduino Nano ESP32 to read value from a light sensor.

If you're in search of a module-based light sensor, I recommend taking a look at the Arduino Nano ESP32 - LDR Light Sensor Module tutorial.

Hardware Preparation

1	×	Arduino Nano ESP32
1	×	USB Cable Type-C
1	×	Light Sensor
1	×	10 kΩ resistor
1	×	Breadboard
1	×	Jumper Wires
1	×	(Optional) DC Power Jack
1	×	(Recommended) Screw Terminal Expansion Board for Arduino Nano
1	×	(Recommended) Breakout Expansion Board for Arduino Nano
1	×	(Recommended) Power Splitter For Arduino Nano ESP32

Or you can buy the following sensor kits:

1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

Disclosure: Some of the links provided in this section are Amazon affiliate links. We may receive a commission for any purchases made through these links at no additional cost to you.
Additionally, some of these links are for products from our own brand, DIYables.

Overview of 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.

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.

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.

Arduino Nano 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 Arduino Nano ESP32 to the photoresistor, we can read the analog value by using analogRead() function.

Wiring Diagram between Light Sensor and Arduino Nano ESP32

The wiring diagram between Arduino Nano ESP32 and Light Sensor

This image is created using Fritzing. Click to enlarge image

Arduino Nano ESP32 Code

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

/* * This Arduino Nano ESP32 code was developed by newbiely.com * * This Arduino Nano ESP32 code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-nano-esp32/arduino-nano-esp32-light-sensor */ #define LIGHT_SENSOR_PIN A0 // The Arduino Nano ESP32 pin connect to the light sensor void setup() { // Initialize the Serial to communicate with the Serial Monitor. Serial.begin(9600); // set the ADC attenuation to 11 dB (up to ~3.3V input) analogSetAttenuation(ADC_11db); } void loop() { // reads the input on analog pin (value between 0 and 4095) int analog_value = analogRead(LIGHT_SENSOR_PIN); Serial.print("Analog Value = "); Serial.print(analog_value); // The raw analog reading // We'll have a few threshholds, qualitatively determined if (analog_value < 40) { Serial.println(" => Dark"); } else if (analog_value < 800) { Serial.println(" => Dim"); } else if (analog_value < 2000) { Serial.println(" => Light"); } else if (analog_value < 3200) { Serial.println(" => Bright"); } else { Serial.println(" => Very bright"); } delay(500); }

Detailed Instructions

If this is the first time you use Arduino Nano ESP32, see how to setup environment for Arduino Nano ESP32 on Arduino IDE.
Copy the above code and paste it to Arduino IDE.
Compile and upload code to Arduino Nano 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
Check out the result on the Serial Monitor. It looks like the below::

COM6

Send

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

Newline

Light Sensor and LED

Wiring Diagram

This image is created using Fritzing. Click to enlarge image

Arduino Nano ESP32 Code

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

/* * This Arduino Nano ESP32 code was developed by newbiely.com * * This Arduino Nano ESP32 code is made available for public use without any restriction * * For comprehensive instructions and wiring diagrams, please visit: * https://newbiely.com/tutorials/arduino-nano-esp32/arduino-nano-esp32-light-sensor */ #define LIGHT_SENSOR_PIN A0 // The Arduino Nano ESP32 pin connect to the light sensor #define LED_PIN D2 // The Arduino NanO ESP32 pin connected to LED #define ANALOG_THRESHOLD 500 void setup() { // set the ADC attenuation to 11 dB (up to ~3.3V input) analogSetAttenuation(ADC_11db); pinMode(LED_PIN, OUTPUT); // set ESP32 pin to output mode } void loop() { int analog_value = analogRead(LIGHT_SENSOR_PIN); // read the value on analog pin if (analog_value < ANALOG_THRESHOLD) digitalWrite(LED_PIN, HIGH); // turn on LED else digitalWrite(LED_PIN, LOW); // turn off LED }

※ NOTE THAT:

This tutorial uses the analogRead() function to read values from an ADC (Analog-to-Digital Converter) connected to a sensor or component. The Arduino Nano ESP32's ADC is suitable for projects that do not require high accuracy. However, for projects needing precise measurements, keep the following in mind:

The Arduino Nano ESP32's ADC is not perfectly accurate and might require calibration for correct results. Each Arduino Nano ESP32 board can vary slightly, so calibration is necessary for each individual board.
Calibration can be challenging, especially for beginners, and might not always yield the exact results you want.

For projects requiring high precision, consider using an external ADC (e.g ADS1115) with the Arduino Nano ESP32 or using another Arduino, such as the Arduino Uno R4 WiFi, which has a more reliable ADC. If you still want to calibrate the Arduino Nano ESP32's ADC, refer to the ESP32 ADC Calibration Driver.

Video Tutorial

Language References

Learn More

Arduino Nano ESP32 - LDR Module

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