要读取环境光传感器数据，需要使用IOKit框架中的IOHID（Reference）
http://iphonedevwiki.net/index.php/AppleISL29003
http://iphonedevwiki.net/index.php/IOKit.framework

我可能已经太晚了，但我从开发人员文档中了解到SensorKit将允许我们这样做，
https://developer.apple.com/documentation/sensorkit/srsensor/3377673-ambientlightsensor

我用摄像机解决了这个问题

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection: (AVCaptureConnection *)connection
{
 CFDictionaryRef metadataDict = CMCopyDictionaryOfAttachments(NULL,
sampleBuffer, kCMAttachmentMode_ShouldPropagate);
NSDictionary *metadata = [[NSMutableDictionary alloc]
                          initWithDictionary:(__bridge NSDictionary*)metadataDict];
CFRelease(metadataDict);
NSDictionary *exifMetadata = [[metadata objectForKey:(NSString *)kCGImagePropertyExifDictionary] mutableCopy];
float brightnessValue = [[exifMetadata objectForKey:(NSString *)kCGImagePropertyExifBrightnessValue] floatValue];

//THIS IS INFORMATION THAT COMES FROM THE SENSOR
_Sensor = [[NSNumber numberWithFloat:brightnessValue] stringValue];
 NSLog(@" %@",_Sensor);

dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, 0.5 * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){

        if ([_Sensor isEqualToString:@"-5.575654"]) {

       // YOU CODE HER

        }
        else {

       // YOU CODE HER
    }

});

}