veml7700

Overview

The veml7700 node reads ambient light intensity from the Vishay VEML7700 sensor via I2C. With a wide dynamic range and configurable gain and integration time, it delivers accurate lux readings from dim indoor environments to bright sunlight. Ideal for automatic display brightness, daylight harvesting, and smart lighting.

Wiring (I2C)

Properties

Output

{
  "payload": {
    "lux": 542.3,
    "white": 610,
    "ambient": 542.3
  },
  "lux": 542.3,
  "white": 610,
  "ambient": 542.3,
  "timestamp": 1640000000000
}

Example: Automatic Display Brightness

Dynamically adjust display backlight based on ambient light to reduce eye strain and save power.

// Function node: Map lux to backlight brightness
var lux = msg.lux;

// Map lux range to brightness percentage (0-100)
var minLux = 1;
var maxLux = 10000;
var minBright = 5;   // Minimum 5% so screen is visible
var maxBright = 100;

// Logarithmic mapping for natural feel
var logLux = Math.log10(Math.max(lux, minLux));
var logMin = Math.log10(minLux);
var logMax = Math.log10(maxLux);

var brightness = minBright + (maxBright - minBright)
    * (logLux - logMin) / (logMax - logMin);
brightness = Math.max(minBright, Math.min(maxBright, brightness));

msg.payload = Math.round(brightness);
msg.topic = "display/backlight";

return msg;

Example: Daylight Harvesting

Adjust artificial lighting to maintain a target lux level, saving energy when natural light is available.

// Function node: Maintain 500 lux target
var lux = msg.lux;
var targetLux = 500;
var tolerance = 50;

var currentDimLevel = flow.get('dimLevel') || 50;
var adjustment = 0;

if (lux < targetLux - tolerance) {
    // Too dark, increase artificial light
    adjustment = Math.min(5, (targetLux - lux) / 50);
} else if (lux > targetLux + tolerance) {
    // Too bright, reduce artificial light
    adjustment = -Math.min(5, (lux - targetLux) / 50);
}

currentDimLevel = Math.max(0, Math.min(100, currentDimLevel + adjustment));
flow.set('dimLevel', currentDimLevel);

msg.payload = {
    measuredLux: lux,
    targetLux: targetLux,
    dimLevel: Math.round(currentDimLevel),
    saving: Math.round(100 - currentDimLevel) + "%"
};

return msg;

Use Cases