UV Index Sensor VEML6075: Measure Sunlight with Arduino

The VEML6075 UV index sensor from Vishay measures both UVA (315-400nm) and UVB (280-315nm) radiation to calculate the standardized UV Index — a critical parameter for sun safety in India, where UV exposure is significantly higher than in European countries. With I2C interface and ±1 UV Index unit accuracy, the VEML6075 is the preferred choice for Arduino-based UV monitoring stations, sunscreen reminder systems, and agricultural light monitoring. This guide covers complete setup, calibration, and real-world applications for Indian weather conditions.

UV Index Basics and India’s Solar UV Exposure

The UV Index (UVI) is a WHO-standardized scale measuring the intensity of UV radiation reaching Earth’s surface. It’s calculated from the erythemally effective irradiance — the UV spectrum weighted by human skin sensitivity to sunburn.

India experiences some of the world’s highest UV indices. Mumbai regularly sees UVI 10-12 from March to October. Rajasthan and Gujarat can reach UVI 13-14 in summer — classified as “extreme.” Coastal Kerala and Tamil Nadu maintain UVI above 8 for 8+ months annually. By contrast, UK averages peak UVI of only 5-7 in summer. This makes UV monitoring particularly important for Indian public health and outdoor worker protection.

VEML6075 Sensor Specifications

• Measures: UVA (315-400nm) and UVB (280-315nm) independently
• UV Index range: 0 to 11+ (extreme conditions in India)
• Interface: I2C (address: 0x10 fixed)
• Integration time: 50ms to 800ms (longer = more sensitive, less noise)
• Dynamic range: 1 to 2241 counts (UVA), 1 to 2241 counts (UVB)
• Supply voltage: 1.7V – 3.6V (3.3V typical)
• Current: 480µA active, 800nA shutdown
• Operating temperature: -40°C to +85°C
• India module price: ₹280-450

I2C Wiring with Arduino and ESP32

/* VEML6075 → Arduino Uno
 * VEML6075 VCC → Arduino 3.3V
 * VEML6075 GND → Arduino GND
 * VEML6075 SCL → Arduino A5 (SCL)
 * VEML6075 SDA → Arduino A4 (SDA)
 * Note: Most modules have 3.3V/5V level shifting onboard
 *
 * VEML6075 → ESP32
 * VEML6075 VCC → ESP32 3.3V
 * VEML6075 GND → ESP32 GND
 * VEML6075 SCL → ESP32 GPIO 22
 * VEML6075 SDA → ESP32 GPIO 21
 */

Arduino Code for UV Index Calculation

// VEML6075 UV Index Sensor - Arduino Library
// Library: Install "VEML6075" by SparkFun via Library Manager
// Or use: Adafruit VEML6075 library

#include <Wire.h>
#include <SparkFun_VEML6075_Arduino_Library.h>

VEML6075 uv;

void setup() {
  Serial.begin(115200);
  Wire.begin();
  
  if (!uv.begin()) {
    Serial.println("VEML6075 not found! Check wiring.");
    while (1);
  }
  
  // Set integration time (longer = more accurate in low UV)
  uv.setIntegrationTime(VEML6075_100MS); // Options: 50MS, 100MS, 200MS, 400MS, 800MS
  
  // Set high dynamic range (for extreme UV in India)
  uv.setHighDynamic(VEML6075_DYNAMIC_HIGH); // Extends range to UVI 16+
  
  Serial.println("VEML6075 UV Sensor Ready");
  Serial.println("UVA_raw, UVB_raw, UVA_cal, UVB_cal, UV_Index, UV_Category");
}

void loop() {
  uv.poll(); // Trigger a new reading
  
  // Raw counts (before calibration)
  float uvaRaw = uv.rawUVA();
  float uvbRaw = uv.rawUVB();
  
  // Calibrated readings (corrected for dark current + visible light)
  float uvaCal = uv.calibratedUVA();
  float uvbCal = uv.calibratedUVB();
  
  // UV Index (library calculates using Vishay formula)
  float uvIndex = uv.index();
  
  String category = getUVCategory(uvIndex);
  
  Serial.print(uvaRaw, 0); Serial.print(", ");
  Serial.print(uvbRaw, 0); Serial.print(", ");
  Serial.print(uvaCal, 1); Serial.print(", ");
  Serial.print(uvbCal, 1); Serial.print(", ");
  Serial.print(uvIndex, 1); Serial.print(", ");
  Serial.println(category);
  
  // Alert for extreme UV (UVI > 8 — very common in India)
  if (uvIndex >= 8) {
    Serial.println("⚠ ALERT: Extreme UV! Seek shade immediately!");
    // Trigger buzzer or LED alert
  }
  
  delay(1000);
}

String getUVCategory(float uvi) {
  if (uvi < 3) return "Low";
  if (uvi < 6) return "Moderate";
  if (uvi < 8) return "High";
  if (uvi < 11) return "Very High";
  return "EXTREME";
}

// Manual UV Index calculation (without library)
// Using Vishay application note coefficients:
float calculateUVIndex(float uva, float uvb) {
  // Compensation coefficients from VEML6075 AN
  float uv_comp_a = uva - 2.22 * uvb;
  float uv_comp_b = uvb - 1.33 * uva;
  
  // UV Index formula
  float uvi = (uv_comp_a * 0.001461) + (uv_comp_b * 0.002424);
  return max(uvi, 0.0f);
}

Calibration and Accuracy

VEML6075’s factory calibration assumes clear-sky direct sunlight measurement. Accuracy can be improved for specific applications:

Verification Against Phone App

UV Index apps (Samsung Weather, AccuWeather) use UV forecast models from satellites. These disagree with ground-truth by ±1-2 UVI due to local cloud cover, air pollution (significant in Indian cities), and elevation differences. Cross-reference your sensor with the ASTM UVIR reference standard data for your city from IMD (India Meteorological Department) website.

Correction for Indian Haze

// Indian urban haze correction factor
// AOD (Aerosol Optical Depth) in major Indian cities is 0.3-0.8
// Higher AOD = more UV scattered = lower actual UV at ground
// Delhi winter: factor ~0.85, Mumbai monsoon: factor ~0.75
// Approximate correction (seasonal, city-specific):

float applyHazeCorrection(float uvIndex, String city, String season) {
  float factor = 1.0;
  if (city == "Delhi" && season == "winter") factor = 0.82;
  else if (city == "Delhi" && season == "summer") factor = 0.90;
  else if (city == "Mumbai") factor = 0.88;
  else if (city == "Rajasthan") factor = 0.95; // Clearer skies
  return uvIndex * factor;
}

Real-World Applications in India

School Playground UV Alert System

Install VEML6075 + ESP32 + LCD at school playgrounds in Rajasthan and Gujarat (highest UV states). Display real-time UV Index with color-coded warning, and activate a buzzer during recess when UV exceeds safe levels. Budget per installation: ₹1200-1500.

Agricultural UV Monitoring

UV-B radiation at 280-315nm affects crop photosynthesis, vitamin D synthesis in animals, and activates certain plant defense mechanisms. Monitoring UV-B alongside temperature and humidity helps agricultural scientists correlate crop yield with solar radiation parameters.

Industrial Rooftop Solar Station

UV Index correlates with solar irradiance (GHI — Global Horizontal Irradiance). When combined with BMP280 (atmospheric pressure, cloud cover proxy) and pyranometer data, VEML6075 helps characterize daily solar resource variability for rooftop solar performance monitoring.

Integration with Weather Station

// Complete weather station with UV, temperature, humidity, pressure
#include <Wire.h>
#include <SparkFun_VEML6075_Arduino_Library.h>
#include <DHT.h>
#include <Adafruit_BMP280.h>

VEML6075 uv;
DHT dht(4, DHT22);
Adafruit_BMP280 bmp;

void setup() {
  Wire.begin();
  Serial.begin(115200);
  uv.begin();
  dht.begin();
  bmp.begin(0x76);
  Serial.println("Weather,Station,Ready");
  Serial.println("Temp(C),Humidity(%),Pressure(hPa),UV_Index,Category");
}

void loop() {
  float temp = dht.readTemperature();
  float hum = dht.readHumidity();
  float pres = bmp.readPressure() / 100.0;
  
  uv.poll();
  float uvIndex = uv.index();
  
  // CSV output for data logging / ThingSpeak upload
  Serial.print(temp, 1); Serial.print(",");
  Serial.print(hum, 1); Serial.print(",");
  Serial.print(pres, 1); Serial.print(",");
  Serial.print(uvIndex, 1); Serial.print(",");
  Serial.println(getUVCategory(uvIndex));
  
  delay(5000); // 5-second intervals
}

Frequently Asked Questions