Access LMU light sensor on Mac. Also includes the Emacs plugin I use for automatically updating my theme according to ambient light.

light.el

;; Light.el
;;
;; Uses the light program to automatically switch themes at certain
;; levels of light

(setq direct-sun 44000000)

(setq light-theme 'solarized-light)
(setq dark-theme 'laravel)

(defun light-level ()
  "Access the level of light detected by the LMU sensor on Macbook Pros"
  (string-to-number (shell-command-to-string "~/.emacs.d/src/light/light") )
)

(defun adjust-theme-to-light ()
  "Picks a theme according to the level of ambient light in the room"
  (if (> (light-level) direct-sun)
    (load-theme light-theme t)
    (load-theme dark-theme t)
    )
)

(adjust-theme-to-light)

light.m

/** 
 * LightSensor
 *
 * Extracted from http://stackoverflow.com/questions/10061028/isight-ambient-sensor 
**/

#include <stdio.h>
#include <IOKit/IOKitLib.h>

#import <Foundation/Foundation.h>

int getLightLevel() 
{
    
    uint32_t outputs = 2;
    uint64_t values[outputs];
	
    io_connect_t port = 0;
	
    // Get the light sensor service
    io_service_t lightSensor = IOServiceGetMatchingService(kIOMasterPortDefault,
                                                           IOServiceMatching("AppleLMUController"));
	
    // Connect the service at the given port
    IOServiceOpen(lightSensor, mach_task_self(), 0, &port);
	
    // Access it, assigning the levels the sensors measure to `values`
    IOConnectCallMethod(port, 0, nil, 0, nil, 0, values, &outputs, nil, 0);
	
    // Disconnects our service 
    IOConnectRelease(lightSensor);

    // Return the first value (I believe this is the iSight camera)
    return (int)values[0];
			
}

int main (int argc, char *argv[]) 
{
    fprintf(stdout, "%i", getLightLevel() );
    return 0;
}

Makefile

all:
  gcc light.m -std=c99 -framework Foundation -framework IOKit -o light  

clean:
  rm -f light