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Arduino - Light Sensor

In this tutorial, we are going to learn:

How light sensor works
How to connect the light sensor to Arduino
How to program Arduino to read the state from the light sensor

If you are looking for a light sensor in the module form, please check out this Arduino - LDR Light Sensor Module tutorial.

Hardware Required

1	×	Arduino UNO or Genuino UNO
1	×	USB 2.0 cable type A/B (for USB-A PC)
1	×	USB 2.0 cable type C/B (for USB-C PC)
1	×	Light Sensor
1	×	10 kΩ resistor
1	×	Breadboard
1	×	Jumper Wires
1	×	(Recommended) Screw Terminal Block Shield for Arduino Uno
1	×	(Recommended) Breadboard Shield For Arduino Uno
1	×	(Recommended) Enclosure For Arduino Uno

Or you can buy the following sensor kits:

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

Disclosure: Some links in this section are Amazon affiliate links. If you make a purchase through these links, we may earn a commission at no extra cost to you.
Additionally, some links direct to products from our own brand, DIYables.

About Light Sensor

The light sensor used in this tutorial is a photoresistor, which is also called light-dependent resistor or photocell.

It is used not only to detect light but also to measure the brightness/illuminance level of the ambient light.

Pinout

A photoresistor has two pins. Since it is a kind of resistor, we do NOT need to distinguish these pins. They are symmetric.

How It Works

The more light the photoresistor's face is exposed, the smaller its resistance is. Therefore, by measuring the photoresistor's resistance, we can know how bright the ambient light is.

The light sensor value only reflects the approximated trend of the intensity of light, it does NOT represent the exact luminous flux. Therefore, it should be used only in an application that does NOT require high accuracy.

Arduino - Light Sensor

Arduino Uno's pin A0 to A5 can work as the analog input. The analog input pin converts the voltage (between 0v and VCC) into integer values (between 0 and 1023), called ADC value or analog value.

By connecting a pin of the photoresistor to an analog input pin, we can read the analog value from the pin by using analogRead() function, and then we can know the light levels relatively.

Wiring Diagram

This image is created using Fritzing. Click to enlarge image

Arduino Code

The below code reads the value from photocell and determine the light level qualitatively

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-light-sensor */ void setup() { // initialize serial communication at 9600 bits per second: Serial.begin(9600); } void loop() { // reads the input on analog pin A0 (value between 0 and 1023) int analogValue = analogRead(A0); Serial.print("Analog reading: "); Serial.print(analogValue); // the raw analog reading // We'll have a few threshholds, qualitatively determined if (analogValue < 10) { Serial.println(" - Dark"); } else if (analogValue < 200) { Serial.println(" - Dim"); } else if (analogValue < 500) { Serial.println(" - Light"); } else if (analogValue < 800) { Serial.println(" - Bright"); } else { Serial.println(" - Very bright"); } delay(500); }

Quick Steps

Copy the above code and open with Arduino IDE
Click Upload button on Arduino IDE to upload code to Arduino
Open Serial Monitor
Radiates light to sensor
See the result on Serial Monitor:

COM6

Send

Analog reading: 163 - Dim Analog reading: 152 - Dim Analog reading: 187 - Dim Analog reading: 188 - Dim Analog reading: 957 - Very bright Analog reading: 972 - Very bright Analog reading: 981 - Very bright

Autoscroll Show timestamp

Clear output

9600 baud

Newline

Light Sensor and LED

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

/* * Created by ArduinoGetStarted.com * * This example code is in the public domain * * Tutorial page: https://arduinogetstarted.com/tutorials/arduino-light-sensor */ // constants won't change const int LIGHT_SENSOR_PIN = A0; // Arduino pin connected to light sensor's pin const int LED_PIN = 3; // Arduino pin connected to LED's pin const int ANALOG_THRESHOLD = 500; // variables will change: int analogValue; void setup() { pinMode(LED_PIN, OUTPUT); // set arduino pin to output mode } void loop() { analogValue = analogRead(LIGHT_SENSOR_PIN); // read the input on analog pin if(analogValue < ANALOG_THRESHOLD) digitalWrite(LED_PIN, HIGH); // turn on LED else digitalWrite(LED_PIN, LOW); // turn off LED }

Wring diagram for the above code:

This image is created using Fritzing. Click to enlarge image

Video Tutorial

We are considering to make the video tutorials. If you think the video tutorials are essential, please subscribe to our YouTube channel to give us motivation for making the videos.

Challenge Yourself

Automatically turn on the light when your room is dark. Hint: Refer to Arduino - Relay.

Language References

The Best Arduino Starter Kit

See the best Arduino kit for beginner

Arduino - Light Sensor

Hardware Required

About Light Sensor

Pinout

How It Works

Arduino - Light Sensor

Wiring Diagram

Arduino Code

Quick Steps

Light Sensor and LED

Video Tutorial

Challenge Yourself

Language References

The Best Arduino Starter Kit

See Also