title: AVCaptureTorchModeAuto does not continuously update torch mode
body: <p>I am writing an app that automatically turns on the torch on the back of an iOS device depending on lighting conditions. The app renders a live camera view, and does not record the video.</p>
  
  <p>I have tried using <code>AVCaptureTorchModeAuto</code>, but it only seems to measure the brightness of the image at the start of the capture session, and set the torch accordingly. The setting then does not change afterwards, regardless of the brightness of the camera image.</p>
  
  <p>It is possible to have the system adjust the torch continuously, like stated in <a href="https://developer.apple.com/library/ios/documentation/AVFoundation/Reference/AVCaptureDevice_Class/#//apple_ref/c/tdef/AVCaptureTorchMode" rel="nofollow">the documentation</a>?</p>
  
  <blockquote>
    <p>The capture device continuously monitors light levels and uses the torch when necessary.</p>
    
    <p>Available in iOS 4.0 and later.</p>
  </blockquote>