Read lux measurement using MBP ambient light sensor.

lmutracker.mm

// lmutracker.mm -- Provides lux measurement using MacBook Ambient Light Sensor
//
// clang -o lmutracker lmutracker.mm -framework IOKit -framework CoreFoundation
//
// Adaptation of code originally posted at https://bugzilla.mozilla.org/show_bug.cgi?id=793728 
// by Reuben Morais. Modified by Ken Keiter <ken@kenkeiter.com> to output a single *lux* value 
// and exit, rather than repeating measurements on the sensor's arbitrary scale.

#include <mach/mach.h>
#include <math.h>
#import <IOKit/IOKitLib.h>
#import <CoreFoundation/CoreFoundation.h>

static double updateInterval = 1;
static io_connect_t dataPort = 0;

int main(void) {
  kern_return_t kr;
  io_service_t serviceObject;
  uint32_t outputs = 2;
  uint64_t values[outputs];
  uint64_t x;
  uint64_t lux;

  serviceObject = IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching("AppleLMUController"));
  if (!serviceObject) {
    fprintf(stderr, "failed to find ambient light sensors\n");
    exit(1);
  }

  kr = IOServiceOpen(serviceObject, mach_task_self(), 0, &dataPort);
  IOObjectRelease(serviceObject);
  if (kr != KERN_SUCCESS) {
    mach_error("IOServiceOpen:", kr);
    exit(kr);
  }

  setbuf(stdout, NULL);

  kr = IOConnectCallMethod(dataPort, 0, nil, 0, nil, 0, values, &outputs, nil, 0);
  if (kr == KERN_SUCCESS) {
    x = values[0];
    lux = (-3*pow(10, -27))*pow(x, 4) + (2.6*pow(10, -19))*pow(x, 3) - (3.4*pow(10,-12))*pow(x, 2) + (3.9*pow(10, -5))*x - 0.19;
    printf("%lld\n", lux);
  }

  exit(0);
}