Try adding support for ambient light sensor

LightSensor.h

+//
+//  LightSensor.h
+//  iTerm
+//
+//  Created by George Nachman on 4/10/13.
+//
+//
+
+#import <Foundation/Foundation.h>
+#include <IOKit/IOKitLib.h>
+#import <Foundation/Foundation.h>
+
+@class LightSensor;
+
+@protocol LightSensorTarget <NSObject>
+- (void)lightSensorMeasuredDarkness:(LightSensor *)lightSensor;
+- (void)lightSensorMeasuredLightness:(LightSensor *)lightSensor;
+@end
+
+@interface LightSensor : NSObject {
+    io_connect_t connection_;
+    NSTimer *timer_;  // weak
+    int64_t darkTriggerLevel_;
+    int64_t lightTriggerLevel_;
+    id<LightSensorTarget> target_;  // weak
+    enum {
+        LightSensorStateLight,
+        LightSensorStateDark
+    } state_;
+}
+
+- (void)startMonitoringWithDarkTriggerLevel:(int64_t)darkTriggerLevel
+                          lightTriggerLevel:(int64_t)lightTriggerLevel
+                                     target:(id<LightSensorTarget>)target;
+
+- (void)stopMonitoring;
+
+- (int64_t)brightness;
+
+@end

LightSensor.m

+//
+//  LightSensor.m
+//  iTerm
+//
+//  Created by George Nachman on 4/10/13.
+//
+//
+
+#import "LightSensor.h"
+#import <mach/mach.h>
+#import <CoreFoundation/CoreFoundation.h>
+
+static NSString * const kLightSensorServiceName = @"AppleLMUController";
+
+@implementation LightSensor
+
++ (io_service_t)ioServiceWithName:(NSString *)serviceName {
+    return IOServiceGetMatchingService(kIOMasterPortDefault, IOServiceMatching([serviceName UTF8String]));
+}
+
+- (id)init {
+    self = [super init];
+    if (self) {
+        io_service_t ioService;
+
+        BOOL ok = NO;
+        ioService = [[self class] ioServiceWithName:kLightSensorServiceName];
+        if (ioService) {
+            kern_return_t status = IOServiceOpen(ioService, mach_task_self(), 0, &connection_);
+            if (status == KERN_SUCCESS) {
+                ok = YES;
+            }
+            IOObjectRelease(ioService);
+        }
+        if (!ok) {
+            [self autorelease];
+            return nil;
+        }
+    }
+    return self;
+}
+
+- (void)notifyTargetOfChange {
+    switch (state_) {
+        case LightSensorStateLight:
+            [target_ lightSensorMeasuredLightness:self];
+            break;
+            
+        case LightSensorStateDark:
+            [target_ lightSensorMeasuredDarkness:self];
+            break;
+    }
+}
+
+- (void)_update:(NSTimer *)timer {
+    int64_t brightness = [self brightness];
+    NSLog(@"Brightness is %lld", brightness);
+    if (brightness > lightTriggerLevel_ && state_ == LightSensorStateDark) {
+        state_ = LightSensorStateLight;
+        [self notifyTargetOfChange];
+    } else if (brightness < darkTriggerLevel_ && state_ == LightSensorStateLight) {
+        state_ = LightSensorStateDark;
+        [self notifyTargetOfChange];
+    }
+}
+
+
+- (void)startMonitoringWithDarkTriggerLevel:(int64_t)darkTriggerLevel
+                          lightTriggerLevel:(int64_t)lightTriggerLevel
+                                     target:(id<LightSensorTarget>)target {
+    darkTriggerLevel_ = darkTriggerLevel;
+    lightTriggerLevel_ = lightTriggerLevel;
+    if ([self brightness] > (darkTriggerLevel_ + lightTriggerLevel_) / 2) {
+        state_ = LightSensorStateLight;
+    } else {
+        state_ = LightSensorStateDark;
+    }
+    target_ = target;
+    
+    [timer_ invalidate];
+    timer_ = [NSTimer scheduledTimerWithTimeInterval:2
+                                              target:self
+                                            selector:@selector(_update:)
+                                            userInfo:nil
+                                             repeats:YES];
+    [self notifyTargetOfChange];
+}
+
+- (void)stopMonitoring {
+    [timer_ invalidate];
+    timer_ = nil;
+    target_ = nil;
+}
+
+- (int64_t)brightness {
+    uint32_t outputs = 2;
+    uint64_t values[outputs];
+    
+    kern_return_t status = IOConnectCallMethod(connection_, 0, nil, 0, nil, 0, values, &outputs, nil, 0);
+    if (status == KERN_SUCCESS) {
+        return values[0] / 2 + values[1] / 2;
+    } else {
+        return -1;
+    }
+}
+
+@end

iTerm.xcodeproj/project.pbxproj

@@ -257,6 +257,9 @@
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+		1D7EE094171679FF0035BAD2 /* LightSensor.h in Headers */ = {isa = PBXBuildFile; fileRef = 1D7EE092171679FF0035BAD2 /* LightSensor.h */; };
+		1D7EE095171679FF0035BAD2 /* LightSensor.m in Sources */ = {isa = PBXBuildFile; fileRef = 1D7EE093171679FF0035BAD2 /* LightSensor.m */; };
+		1D7EE097171682040035BAD2 /* IOKit.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 1D7EE096171682040035BAD2 /* IOKit.framework */; };
 		1D823C4812F92B3F0028422B /* screen.png in Resources */ = {isa = PBXBuildFile; fileRef = 1D823C4712F92B3F0028422B /* screen.png */; };
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@@ -568,6 +571,9 @@
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+		1D7EE092171679FF0035BAD2 /* LightSensor.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = LightSensor.h; sourceTree = "<group>"; };
+		1D7EE093171679FF0035BAD2 /* LightSensor.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = LightSensor.m; sourceTree = "<group>"; };
+		1D7EE096171682040035BAD2 /* IOKit.framework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.framework; name = IOKit.framework; path = Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.6.sdk/System/Library/Frameworks/IOKit.framework; sourceTree = DEVELOPER_DIR; };
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@@ -845,6 +851,7 @@
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 			buildActionMask = 2147483647;
 			files = (
+				1D7EE097171682040035BAD2 /* IOKit.framework in Frameworks */,
 				874206530564169600CFC3F1 /* AppKit.framework in Frameworks */,
 				F6E2DEDA0AE2F67200D20B3B /* Sparkle.framework in Frameworks */,
 				1D13EADC12113A2D00909F9C /* libncurses.dylib in Frameworks */,
@@ -861,6 +868,7 @@
 		0464AB0D006CD2EC7F000001 /* JTerminal */ = {
 			isa = PBXGroup;
 			children = (
+				1D7EE096171682040035BAD2 /* IOKit.framework */,
 				0464AB0E006CD2EC7F000001 /* Classes */,
 				0464AB15006CD2EC7F000001 /* Headers */,
 				0464AB1F006CD2EC7F000001 /* Other Sources */,
@@ -919,6 +927,8 @@
 				F69E788C0AB7AC6D001EC0FF /* iTermGrowlDelegate.m */,
 				DDDB7ABD05D7736600E197C2 /* iTermKeyBindingMgr.m */,
 				1DAED99112EDF923005E49ED /* iTermSearchField.m */,
+				1D7EE092171679FF0035BAD2 /* LightSensor.h */,
+				1D7EE093171679FF0035BAD2 /* LightSensor.m */,
 				1D72438C11F416E500BD4924 /* LineBuffer.m */,
 				1D29732614082676004C5DBE /* MovePaneController.m */,
 				1D085F8416F02E7400B7FCE9 /* PasteContext.h */,
@@ -1650,6 +1660,7 @@
 				1D085F9A16F1135F00B7FCE9 /* PasteEvent.h in Headers */,
 				1D085F9E16F137D900B7FCE9 /* RoundedRectView.h in Headers */,
 				1D085FA216F138A100B7FCE9 /* ToastWindowController.h in Headers */,
+				1D7EE094171679FF0035BAD2 /* LightSensor.h in Headers */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};
@@ -1972,6 +1983,7 @@
 				1D085F9B16F1135F00B7FCE9 /* PasteEvent.m in Sources */,
 				1D085F9F16F137D900B7FCE9 /* RoundedRectView.m in Sources */,
 				1D085FA316F138A100B7FCE9 /* ToastWindowController.m in Sources */,
+				1D7EE095171679FF0035BAD2 /* LightSensor.m in Sources */,
 			);
 			runOnlyForDeploymentPostprocessing = 0;
 		};

iTermApplicationDelegate.m

@@ -28,6 +28,7 @@
 #import "iTermApplicationDelegate.h"
 #import "iTermController.h"
 #import "ITAddressBookMgr.h"
+#import "LightSensor.h"
 #import "PreferencePanel.h"
 #import "PseudoTerminal.h"
 #import "PTYSession.h"
@@ -587,7 +588,9 @@ static BOOL hasBecomeActive = NO;
 - (id)init
 {
     self = [super init];
-
+    LightSensor *ls = [[LightSensor alloc] init];
+    [ls startMonitoringWithDarkTriggerLevel:100 lightTriggerLevel:200 target:nil];
+    
     // Add ourselves as an observer for notifications.
     [[NSNotificationCenter defaultCenter] addObserver:self
                                              selector:@selector(reloadMenus:)