BH1750 Digital Light Sensor

The BH1750 is a digital ambient light sensor that measures illuminance (light intensity) in lux and communicates over I2C. Unlike a simple photoresistor (LDR), the BH1750 outputs a calibrated digital value directly in lux, so there is no need for analog-to-digital conversion or manual calibration. It is an ideal sensor for projects that need accurate, repeatable light measurements.

This guide uses the ESP32-WROOM-32 DevKit. Pin labels may differ on your board -- check your board's pinout diagram.

Alternatives: For simple light/dark detection where calibrated lux values are not needed, an LDR is cheaper and simpler (no library, no I2C). See our light sensor comparison for a full breakdown.

🔗Key Specs

🔗What Is Lux?

Lux (lx) is the standard unit of illuminance -- it measures how much light falls on a surface. Here are some reference values to give you an intuitive sense:

These values are useful for setting thresholds in your projects -- for example, turning on a light when the reading drops below $200\,\text{lx}$.

🔗What You'll Need

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🔗Wiring (I2C)

Pin labels, GPIO numbers, and ADC channels vary between ESP32 boards. GPIOs 21 (SDA) and 22 (SCL) are the default I2C pins on most ESP32-WROOM-32 DevKit boards, but your board may differ. Always check your board's pinout diagram.

🔗I2C Address

The ADDR pin controls the I2C address:

• ADDR connected to GND (or left floating): address is 0x23
• ADDR connected to VCC: address is 0x5C

This lets you use two BH1750 sensors on the same I2C bus with different addresses.

🔗Required Libraries

Install the following through the Arduino Library Manager:

1. BH1750 by Christopher Laws -- provides a straightforward API for the sensor

To install:

1. Go to Sketch > Include Library > Manage Libraries...
2. Search for BH1750 and install the library by Christopher Laws

No additional dependencies are needed beyond the built-in Wire.h library.

🔗Code Example

This sketch reads the light level in lux from the BH1750 sensor and prints it to the Serial Monitor every second.

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

BH1750 lightMeter;

void setup() {
    Serial.begin(115200);
    Wire.begin();  // Initialize I2C (SDA = GPIO 21, SCL = GPIO 22)

    if (lightMeter.begin(BH1750::CONTINUOUS_HIGH_RES_MODE)) {
        Serial.println("BH1750 sensor initialized.");
    } else {
        Serial.println("Error: Could not find BH1750 sensor.");
        Serial.println("Check wiring and I2C address.");
        while (1) delay(10);  // Halt
    }
}

void loop() {
    float lux = lightMeter.readLightLevel();

    if (lux < 0) {
        Serial.println("Error reading light level.");
    } else {
        Serial.print("Light: ");
        Serial.print(lux, 1);
        Serial.println(" lx");
    }

    delay(1000);
}

🔗Using Two Sensors

If you connect two BH1750 sensors with different ADDR settings, you can read both:

BH1750 lightMeter1(0x23);  // ADDR = GND
BH1750 lightMeter2(0x5C);  // ADDR = VCC

void setup() {
    Serial.begin(115200);
    Wire.begin();
    lightMeter1.begin(BH1750::CONTINUOUS_HIGH_RES_MODE);
    lightMeter2.begin(BH1750::CONTINUOUS_HIGH_RES_MODE);
}

void loop() {
    float lux1 = lightMeter1.readLightLevel();
    float lux2 = lightMeter2.readLightLevel();

    Serial.print("Sensor 1: ");
    Serial.print(lux1, 1);
    Serial.print(" lx  |  Sensor 2: ");
    Serial.print(lux2, 1);
    Serial.println(" lx");

    delay(1000);
}

🔗How It Works

The BH1750 contains an integrated photodiode and a 16-bit analog-to-digital converter. It measures the intensity of visible light hitting the sensor and converts it to a digital lux value internally. The sensor's spectral response is designed to approximate the sensitivity of the human eye, which makes its readings feel intuitive.

In continuous high-resolution mode (the default in our code), the sensor takes a new reading approximately every $120\,\text{ms}$ and makes the latest value available over I2C whenever you request it.

🔗Troubleshooting

🔗Next Steps

• Build an automatic desk lamp that adjusts brightness based on ambient light levels
• Create a daylight logger that tracks light levels throughout the day
• Combine the BH1750 with a relay to control outdoor lights at dusk
• Pair it with a BME280 for a complete environmental monitoring station