How to Interface BH1750 Light Sensor with Arduino & ESP32

The BH1750 light sensor is one of the most popular digital ambient light sensors used in hobby electronics and professional projects. Whether you’re building an automatic lamp controller, a smart greenhouse monitor, or a weather station, the BH1750 gives you accurate lux readings over I2C without the headaches of analog conversion. In this comprehensive guide, you’ll learn everything you need to interface the BH1750 with both Arduino and ESP32, from wiring to code to real-world deployment.

What Is the BH1750 Light Sensor?

The BH1750 is a 16-bit digital ambient light sensor IC manufactured by ROHM Semiconductor. Unlike analog LDR (Light Dependent Resistor) modules that require ADC conversion and calibration, the BH1750 directly outputs light intensity in lux units via the I2C protocol. This makes it incredibly easy to integrate with any microcontroller that supports I2C communication.

The sensor is sensitive to visible light and has a spectral response close to the human eye, making its lux readings highly accurate for human-centric lighting applications. It’s widely used in smartphones, tablets, and embedded systems for automatic brightness control.

Key Specifications

• Supply Voltage: 2.4V to 3.6V (VCC pin), logic level 1.8V to 3.6V
• Measurement Range: 1 to 65,535 lux
• Resolution: 1 lux (standard mode), 0.5 lux (high resolution mode)
• Interface: I2C (up to 400 kHz Fast Mode)
• I2C Addresses: 0x23 (ADDR pin LOW) or 0x5C (ADDR pin HIGH)
• Measurement Time: 120 ms (high resolution), 16 ms (low resolution)
• Operating Temperature: -40°C to +85°C
• Current Consumption: 0.12 mA (active), 0.01 mA (power down)
• No External Components Required

The GY-302 breakout board (the most common BH1750 module) includes an onboard 3.3V regulator and level shifters, making it safe to use directly with 5V Arduino boards without a separate level converter.

How It Works

The BH1750 uses a photodiode array that converts incident light into a current proportional to the lux level. This current is then integrated and digitized by a built-in 16-bit ADC. The digital result is transmitted over I2C to your microcontroller. Here’s the internal flow:

1. Photodiode captures incoming photons and generates a current
2. Integration circuit collects the charge over a set measurement time
3. ADC converts the charge to a 16-bit digital value
4. I2C output register holds the result ready for reading

The raw register value is divided by 1.2 to get the lux reading: Lux = Raw Value / 1.2. In high-resolution mode 2, this becomes Lux = Raw Value / 2.4.

Wiring BH1750 with Arduino

Connecting the BH1750 (GY-302 module) to an Arduino Uno or Nano is straightforward. The module uses I2C, so only 4 wires are needed:

Note for Arduino Mega: SDA is pin 20, SCL is pin 21. For Arduino Leonardo: SDA is pin 2, SCL is pin 3.

The GY-302 module already has 4.7kΩ pull-up resistors on SDA and SCL lines, so you don’t need external pull-ups when using this breakout board.

Wiring BH1750 with ESP32

The ESP32 runs at 3.3V logic, which is perfectly compatible with the BH1750. The default I2C pins on most ESP32 dev boards are:

You can reassign I2C pins on ESP32 using the Wire.begin(SDA_PIN, SCL_PIN) function, giving you full flexibility for custom PCB designs.

Installing the Library

The easiest library for BH1750 is the BH1750 by Christopher Laws, available directly in the Arduino Library Manager. To install it:

1. Open Arduino IDE
2. Go to Sketch → Include Library → Manage Libraries
3. Search for “BH1750”
4. Click Install on “BH1750 by Christopher Laws”

Alternatively, for PlatformIO, add lib_deps = claws/BH1750@^1.3.0 to your platformio.ini.

Arduino Code & Explanation

Here’s a complete working sketch for Arduino to read lux values from the BH1750 every second:

#include <Wire.h>
#include <BH1750.h>

BH1750 lightMeter;

void setup() {
  Serial.begin(9600);
  Wire.begin();
  
  if (lightMeter.begin(BH1750::CONTINUOUS_HIGH_RES_MODE)) {
    Serial.println("BH1750 initialized successfully");
  } else {
    Serial.println("Error initializing BH1750");
    while (1); // Halt if sensor not found
  }
}

void loop() {
  if (lightMeter.measurementReady()) {
    float lux = lightMeter.readLightLevel();
    Serial.print("Light: ");
    Serial.print(lux);
    Serial.println(" lx");
  }
  delay(1000);
}

Code Explanation:

• BH1750::CONTINUOUS_HIGH_RES_MODE — enables continuous measurement at 1 lux resolution
• lightMeter.measurementReady() — checks if the sensor has completed a measurement
• lightMeter.readLightLevel() — returns the lux value as a float

Open the Serial Monitor at 9600 baud and you’ll see live lux readings updating every second.

ESP32 Code & IoT Integration

The ESP32 code is nearly identical but includes Wi-Fi capability for IoT use cases. Here’s an example that reads BH1750 values and publishes them to an MQTT broker:

#include <Wire.h>
#include <BH1750.h>
#include <WiFi.h>
#include <PubSubClient.h>

const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";
const char* mqttServer = "broker.hivemq.com";
const int mqttPort = 1883;
const char* mqttTopic = "zbotic/light";

BH1750 lightMeter;
WiFiClient espClient;
PubSubClient client(espClient);

void setup() {
  Serial.begin(115200);
  Wire.begin(21, 22); // SDA=21, SCL=22
  lightMeter.begin(BH1750::CONTINUOUS_HIGH_RES_MODE);

  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("nWiFi connected!");

  client.setServer(mqttServer, mqttPort);
}

void loop() {
  if (!client.connected()) {
    client.connect("ESP32_BH1750");
  }
  client.loop();

  if (lightMeter.measurementReady()) {
    float lux = lightMeter.readLightLevel();
    char luxStr[10];
    dtostrf(lux, 6, 2, luxStr);
    client.publish(mqttTopic, luxStr);
    Serial.printf("Published: %s luxn", luxStr);
  }
  delay(5000);
}

This setup allows you to monitor ambient light levels remotely — perfect for smart home dashboards (Home Assistant, Node-RED) or automated lighting systems.

Measurement Modes Explained

The BH1750 supports multiple measurement modes that trade off speed against resolution:

Pro tip: Use ONE_TIME_HIGH_RES_MODE in battery-powered projects. The sensor automatically powers down after each measurement, reducing current consumption dramatically.

I2C Address Selection

One powerful feature of the BH1750 is that you can run two sensors on the same I2C bus by using the ADDR pin:

• ADDR = LOW (GND): I2C address 0x23 (default)
• ADDR = HIGH (VCC/3.3V): I2C address 0x5C

To use a custom address in code:

BH1750 lightMeter1(0x23); // ADDR pin to GND
BH1750 lightMeter2(0x5C); // ADDR pin to 3.3V

lightMeter1.begin();
lightMeter2.begin();

This is useful in differential light measurement setups, such as comparing sunlight on top of a structure vs. shaded areas below.

Real-World Applications

• Automatic Street/Room Lighting: Turn lights on when lux drops below a threshold (e.g., 50 lux)
• Smart Greenhouse: Monitor sunlight levels and trigger grow lights when clouds reduce natural light
• Solar Panel Optimization: Track irradiance to calculate panel efficiency
• Photography Assistant: Build an Arduino light meter for camera exposure calculation
• Weather Station: Add cloud cover estimation alongside BMP280 pressure data
• Screen Auto-Brightness: Adjust LCD backlight PWM based on ambient lux
• Security Systems: Detect sudden changes in light that might indicate an intrusion

BMP280 Barometric Pressure and Altitude Sensor I2C/SPI Module

Pair with BH1750 to build a complete weather station — measures pressure, altitude, and temperature alongside your light readings on the same I2C bus.

View on Zbotic

DHT11 Digital Relative Humidity and Temperature Sensor Module

Add temperature and humidity sensing to your BH1750 light project for a comprehensive environmental monitoring station.

View on Zbotic

Troubleshooting Tips

• “Error initializing BH1750”: Check your wiring. Use an I2C scanner sketch to confirm the sensor is detected at address 0x23 or 0x5C.
• Always reading 0 lux: Ensure the ADDR pin is connected (even to GND). A floating ADDR pin causes unstable addresses.
• Inconsistent readings: Add bypass capacitors (100nF) between VCC and GND close to the sensor pin.
• I2C conflict: If another sensor shares the bus, check for address conflicts. BH1750’s 0x23 clashes with SHT21/SI7021 in some configurations.
• ESP32 I2C timeout: Slow I2C speed by calling Wire.setClock(100000) before initialization.
• GY-302 on 5V Arduino: The module’s onboard regulator handles 5V input. Do NOT apply 5V to the VCC pin of the bare IC — it only accepts 3.6V max.

Frequently Asked Questions