main.js

var i2c = require('i2c');
var address = 0x39;
var wire = new i2c(address, {device: '/dev/i2c-1'});
var express = require('express');
var app = express();

app.get('/', function (req, res) {
  readLux(function (err, luxVal) {
    err && console.log(err.toString());
    luxVal && console.log('Lux: ' + luxVal);

    res.send({ lux: luxVal, error: err && err.toString() });
  });
});

app.listen(3000, function () {
  setUpSensor();
  console.log('Example app listening on port 3000!');
});

function setUpSensor() {
  wire.writeBytes(0x80, [0x03], noop);
}

function readLightData(address, cb) {
  wire.readBytes(address, 2, function(err, res) {
    if (err) {      
      cb && cb(err);
      return;
    }

    var val = (res[1] << 8) + res[0];
    cb && cb(undefined, val);
    
    val === 0 && setUpSensor();
  });
}

function calculateLux(ch0, ch1) {
  var self = this;
  var gainMultiplier = 1;
  var timeMultiplier = 1;
  var scaling;
  var lux = 0;
  var channelRatio = 1;

  scaling = timeMultiplier * gainMultiplier;
  ch0 *= scaling;
  ch1 *= scaling;
  channelRatio = ch1 / ch0;
  console.log('channelRatio: ' + channelRatio); 

  // T/FN/CL
  if ((0 < channelRatio) && (channelRatio <= 0.50)) {
    lux = 0.0304 * ch0 - 0.062 * ch0 * Math.pow(channelRatio, 1.4);
    console.log('lux: ' + lux);
  } else if ((0.50 < channelRatio) && (channelRatio <= 0.61)) {
    lux = 0.0224 * ch0 - 0.031 * ch1;
  } else if ((0.61 < channelRatio) && (channelRatio <= 0.80)) {
    lux = 0.0128 * ch0 - 0.0153 * ch1;
  } else if ((0.80 < channelRatio) && (channelRatio <= 1.30)) {
    lux = 0.00146 * ch0 - 0.00112 * ch1;
  } else if (channelRatio > 1.30) {
    lux = 0;
  }

  return Math.round(lux * 100) / 100;
}

function readLux(cb) {
  readLightData(0xAC, function (err0, ch0) {
    if (err0) {
      cb && cb(err0);
      return;
    }

    readLightData(0xAE, function (err1, ch1) {
      if (err1) {
        cb && cb(err1);
        return;
      }

      var luxVal = calculateLux(ch0, ch1);
      cb && cb(undefined, luxVal);
      console.log(luxVal);
    });
  });  
}

function noop() { }