UV Sensor Arduino: Ultraviolet Light Measurement

Monitoring ultraviolet radiation matters for health applications, weather stations, and environmental sensing projects. The UV Sensor Arduino combination provides accessible measurement of invisible UV rays that affect human skin and various materials.

After building several UV index meters and integrating these sensors into outdoor monitoring systems, I’ve learned the nuances of each sensor type and their practical limitations. This guide covers the popular UV sensor options, wiring configurations, and code examples to get reliable ultraviolet measurements.

Understanding Ultraviolet Radiation

Ultraviolet light occupies the electromagnetic spectrum between visible light and X-rays, with wavelengths from approximately 10nm to 400nm. For practical measurement with Arduino sensors, three UV bands matter:

UV Band	Wavelength Range	Characteristics
UVA	315-400 nm	Tanning rays, reaches Earth’s surface
UVB	280-315 nm	Burning rays, partially absorbed by ozone
UVC	100-280 nm	Germicidal, blocked by atmosphere

Most Arduino UV sensors detect UVA and UVB wavelengths since UVC from the sun doesn’t reach Earth’s surface. The UV Index, developed by Canadian scientists in 1992 and standardized by the World Health Organization, provides a standardized scale for expressing UV intensity relative to skin damage potential.

UV Index Scale and Health Guidelines

The UV Index directly correlates to sunburn risk:

UV Index	Exposure Level	Protection Required
0-2	Low	Minimal protection needed
3-5	Moderate	Wear sunscreen, seek shade at midday
6-7	High	Reduce sun exposure 10am-4pm
8-10	Very High	Extra protection essential
11+	Extreme	Avoid outdoor exposure

Building a UV meter with Arduino lets you monitor real-time conditions rather than relying on weather forecasts that may not reflect your specific location and time.

Popular UV Sensors for Arduino Projects

Several UV sensor modules work with Arduino, each with distinct characteristics:

ML8511 UV Sensor

The ML8511 from ROHM Semiconductor detects 280-390nm wavelengths covering UVB and most of UVA spectrum. It outputs an analog voltage linearly proportional to UV intensity (mW/cm²), making it straightforward to interface with Arduino’s ADC.

Specification	Value
Detection Range	280-390 nm
Output Type	Analog voltage
Output Range	1.0V (no UV) to 2.8V (15 mW/cm²)
Supply Voltage	3.3V
Current Consumption	300 µA (typical)

GUVA-S12SD UV Sensor

The GUVA-S12SD is a Schottky-type photodiode sensitive to 200-370nm wavelengths. Modules typically include an op-amp to convert the nanoampere photocurrent into a readable voltage signal.

Specification	Value
Detection Range	200-370 nm
Output Type	Analog voltage
Response Time	<0.5 seconds
Supply Voltage	2.7-5.5V
Operating Temperature	-30°C to +85°C

VEML6075 Digital UV Sensor

The VEML6075 provides separate UVA and UVB channel readings via I2C interface. Built-in calibration registers simplify UV Index calculation.

Specification	Value
UVA Detection	320-410 nm
UVB Detection	280-315 nm
Interface	I2C
I2C Address	0x10
Resolution	16-bit
Supply Voltage	1.7-3.6V

LTR-390UV Digital UV Sensor

The LTR-390UV offers both ambient light and UV sensing modes with I2C communication. It provides direct UV Index calculation support.

Specification	Value
UV Detection	280-430 nm
Interface	I2C
I2C Address	0x53
Gain Options	1×, 3×, 6×, 9×, 18×
Supply Voltage	2.5-3.6V

Wiring ML8511 to Arduino

The ML8511 requires careful attention to the 3.3V reference for accurate readings:

ML8511 Pin	Arduino UNO	Notes
VIN	3.3V	Power supply
GND	GND	Common ground
OUT	A0	Analog output
EN	3.3V	Enable pin (tie high)
3.3V	A1	Reference voltage for calibration

Connecting the Arduino 3.3V pin to an analog input (A1) allows using it as a precise reference voltage, improving measurement accuracy regardless of variations in VCC.

ML8511 Arduino Code Example

This code reads UV intensity and calculates the UV Index:

int UVOUT = A0;    // UV sensor output

int REF_3V3 = A1;  // 3.3V reference

void setup() {

  Serial.begin(9600);

  pinMode(UVOUT, INPUT);

  pinMode(REF_3V3, INPUT);

  Serial.println(“ML8511 UV Sensor”);

}

void loop() {

  int uvLevel = averageAnalogRead(UVOUT);

  int refLevel = averageAnalogRead(REF_3V3);

  // Calculate output voltage using 3.3V reference

  float outputVoltage = 3.3 / refLevel * uvLevel;

  // Convert voltage to UV intensity (mW/cm²)

  float uvIntensity = mapfloat(outputVoltage, 0.99, 2.8, 0.0, 15.0);

  Serial.print(“Output: “);

  Serial.print(outputVoltage);

  Serial.print(” V  UV Intensity: “);

  Serial.print(uvIntensity);

  Serial.println(” mW/cm²”);

  delay(1000);

}

int averageAnalogRead(int pinToRead) {

  int numberOfReadings = 8;

  int runningValue = 0;

  for (int i = 0; i < numberOfReadings; i++) {

    runningValue += analogRead(pinToRead);

  }

  return runningValue / numberOfReadings;

}

float mapfloat(float x, float in_min, float in_max, float out_min, float out_max) {

  return (x – in_min) * (out_max – out_min) / (in_max – in_min) + out_min;

}

The averaging function reduces noise, and the custom mapfloat() handles floating-point conversion that Arduino’s built-in map() doesn’t support.

Wiring GUVA-S12SD to Arduino

The GUVA-S12SD module has a simpler three-wire connection:

GUVA-S12SD Pin	Arduino UNO	Notes
VCC	5V	Power supply
GND	GND	Common ground
OUT	A0	Analog output (0-1V typical)

GUVA-S12SD Arduino Code Example

This code converts sensor voltage to UV Index:

void setup() {

  Serial.begin(9600);

  Serial.println(“GUVA-S12SD UV Sensor”);

}

void loop() {

  int sensorValue = analogRead(A0);

  float voltage = sensorValue * (5.0 / 1023.0);

  // Convert voltage to UV Index

  // Based on sensor datasheet: ~0.1V per UV Index point

  float uvIndex = voltage / 0.1;

  Serial.print(“Voltage: “);

  Serial.print(voltage, 3);

  Serial.print(” V  UV Index: “);

  Serial.println(uvIndex, 1);

  delay(1000);

}

Note that GUVA-S12SD modules vary in amplification circuitry. Some “purple” PCB variants have excessive gain making them unsuitable for outdoor sunlight measurement. Check your specific module’s output range.

Using Digital UV Sensors (VEML6075)

Digital sensors like the VEML6075 communicate via I2C and include onboard UV Index calculation:

#include <Wire.h>

#include “Adafruit_VEML6075.h”

Adafruit_VEML6075 uv = Adafruit_VEML6075();

void setup() {

  Serial.begin(9600);

  Serial.println(“VEML6075 UV Sensor”);

  if (!uv.begin()) {

    Serial.println(“Sensor not found!”);

    while (1);

  }

  Serial.println(“Sensor initialized”);

}

void loop() {

  Serial.print(“UVA: “);

  Serial.print(uv.readUVA());

  Serial.print(”  UVB: “);

  Serial.print(uv.readUVB());

  Serial.print(”  UV Index: “);

  Serial.println(uv.readUVI());

  delay(1000);

}

Install the Adafruit VEML6075 library through the Arduino Library Manager before uploading.

UV Sensor Comparison Table

Choosing the right sensor depends on your project requirements:

Feature	ML8511	GUVA-S12SD	VEML6075	LTR-390UV
Interface	Analog	Analog	I2C	I2C
UV Bands	UVA+UVB	UVA+UVB	UVA, UVB separate	UVA+UVB
UV Index Calculation	Manual	Manual	Built-in	Built-in
Power Consumption	300 µA	Low	100 µA	110 µA
Price Range	$3-5	$2-4	$5-8	$5-8
Complexity	Low	Low	Medium	Medium

Analog sensors work well for simple projects where approximate UV levels suffice. Digital sensors provide better accuracy and separate UVA/UVB measurements for more sophisticated applications.

Calibration and Accuracy Considerations

Consumer-grade UV sensors have inherent limitations. The relationship between sensor output and true UV Index depends on several factors:

Spectral response curves differ from the erythemal action spectrum used to define UV Index. Sensors respond to all wavelengths in their detection range, while UV Index weights different wavelengths according to their skin damage potential.

Cosine response affects readings at angles. Professional UV meters use diffusers to ensure accurate measurements regardless of sun angle. Most hobby sensors lack this feature.

Temperature affects semiconductor sensor performance. Outdoor measurements in hot conditions may drift from calibrated values.

For relative measurements and trend monitoring, these sensors work adequately. For absolute UV Index values matching weather service reports, expect ±1-2 index points variance.

Practical Project: UV Index Meter with Display

Combine the UV sensor with an OLED display for a portable UV meter:

Wire an SSD1306 OLED (I2C) alongside your chosen UV sensor. The OLED connects to the same I2C bus (SDA/SCL) as digital UV sensors, or independently if using analog sensors.

Add a visual indicator showing exposure risk level based on measured UV Index. Color-coded warnings (green/yellow/orange/red) help users quickly assess protection needs.

Consider battery operation for portability. Both analog UV sensors and the microcontroller can operate from a single lithium battery with appropriate regulation.

Troubleshooting Common Issues

Readings Always Zero or Very Low

Verify sensor orientation—the detecting element must face the UV source. Indoor lighting produces minimal UV; test outdoors in sunlight.

Saturated or Maximum Readings

Some module variants have excessive amplification. Reduce gain if adjustable, or use a different module designed for outdoor intensity levels.

Inconsistent Values

Average multiple readings to reduce noise. Ensure stable power supply and secure connections. Rapid fluctuations may indicate wiring issues.

Readings Don’t Match Weather Reports

Weather service UV Index represents calculated values based on solar angle, ozone, and cloud cover. Your sensor measures actual incident UV at your specific location. Some variance is expected.

Useful Resources and Downloads

Resource	Description
ML8511 Datasheet	ROHM sensor specifications
GUVA-S12SD Datasheet	GenUV sensor specifications
VEML6075 Datasheet	Vishay digital UV sensor
Adafruit VEML6075 Library	Arduino library
Adafruit LTR390 Library	Arduino library
SparkFun ML8511 Guide	Detailed hookup tutorial

Frequently Asked Questions

Which UV sensor is most accurate for Arduino projects?

Digital sensors like the VEML6075 and LTR-390UV provide better accuracy due to built-in calibration and separate UVA/UVB channels. The LTR-390UV specifically includes UV Index calculation algorithms validated against reference instruments.

Can I measure UV from artificial sources like UV LEDs?

Yes, these sensors detect UV from any source within their wavelength range. UV LEDs typically emit in the UVA band (365-405nm). Ensure the sensor’s detection range covers your specific UV source wavelength.

Why do my readings differ from weather app UV Index?

Weather apps report forecast values based on solar calculations, not actual measurements. Your sensor measures real conditions at your location, which may differ due to cloud cover, reflective surfaces, or local atmospheric conditions.

How do I protect the sensor for outdoor use?

Use UV-transparent enclosures or position the sensor under a quartz or borosilicate glass cover. Standard glass and plastic block significant UV radiation and will cause low readings. PTFE diffusers improve angular response while protecting the sensor.

Can these sensors detect UVC for germicidal lamp monitoring?

The GUVA-S12SD has sensitivity down to 200nm, covering UVC wavelengths. However, UVC measurements require careful safety protocols—direct UVC exposure damages eyes and skin rapidly. Ensure proper shielding when working with UVC sources.

Building Effective UV Monitoring Systems

The UV Sensor Arduino combination enables practical ultraviolet measurement for health monitoring, weather stations, and material testing applications. Analog sensors like the ML8511 and GUVA-S12SD offer simplicity, while digital options like the VEML6075 provide enhanced accuracy and separate UVA/UVB data.

Start with the basic code examples to verify sensor operation, then integrate displays and data logging for complete UV monitoring solutions. Remember that hobby-grade sensors provide useful relative measurements but may not match laboratory-calibrated instruments in absolute accuracy.

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“Learn to measure ultraviolet light with UV Sensor Arduino projects. Compare ML8511, GUVA-S12SD, and VEML6075 sensors with wiring diagrams, code examples, and UV Index calculation.”

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